Fireworks degrade air quality, reduce visibility, alter atmospheric
chemistry, and cause short-term adverse health effects. However, there have
not been any comprehensive physicochemical and optical measurements of
fireworks and their associated impacts in a Southeast Asia megacity, where
fireworks are a regular part of the culture. Size-resolved particulate
matter (PM) measurements were made before, during, and after New Year 2019
at the Manila Observatory in Quezon City, Philippines, as part of the Cloud,
Aerosol, and Monsoon Processes Philippines Experiment (CAMP2Ex). A high-spectral-resolution lidar (HSRL) recorded a substantial increase in
backscattered signal associated with high aerosol loading ∼440 m above the surface during the peak of firework activities around 00:00 (local time). This was accompanied by PM2.5 concentrations peaking at
383.9 µg m-3. During the firework event, water-soluble ions
and elements, which affect particle formation, growth, and fate, were mostly
in the submicrometer diameter range. Total (>0.056µm)
water-soluble bulk particle mass concentrations were enriched by 5.7 times
during the fireworks relative to the background (i.e., average of before and
after the firework). The water-soluble mass fraction of PM2.5 increased by 18.5 % above that of background values. This corresponded
to increased volume fractions of inorganics which increased bulk
particle hygroscopicity, kappa (κ), from 0.11 (background) to 0.18
(fireworks). Potassium and non-sea-salt (nss) SO42- contributed
the most (70.9 %) to the water-soluble mass, with their mass size
distributions shifting from a smaller to a larger submicrometer mode during
the firework event. On the other hand, mass size distributions for
NO3-, Cl-, and Mg2+ (21.1 % mass contribution) shifted
from a supermicrometer mode to a submicrometer mode. Being both uninfluenced
by secondary aerosol formation and constituents of firework materials, a
subset of species were identified as the best firework tracer species (Cu,
Ba, Sr, K+, Al, and Pb). Although these species (excluding K+)
only contributed 2.1 % of the total mass concentration of water-soluble
ions and elements, they exhibited the highest enrichments (6.1 to 65.2)
during the fireworks. Surface microscopy analysis confirmed the presence of
potassium/chloride-rich cubic particles along with capsule-shaped particles
in firework samples. The results of this study highlight how firework
emissions change the physicochemical and optical properties of water-soluble
particles (e.g., mass size distribution, composition, hygroscopicity, and
aerosol backscatter), which subsequently alters the background aerosol's
respirability, influence on surroundings, ability to uptake gases, and
viability as cloud condensation nuclei (CCN).
Introduction
Fireworks affect local populations through visibility reduction and
increased health risks due to briefly elevated particulate matter (PM)
levels. Total PM mass concentrations during local celebrations in the
following cities exceeded the 24 h US National Ambient Air Quality
Standard (NAAQS) for PM10 of 150 µg m-3: Leipzig, Germany,
(Wehner et al., 2000); Brownsville, Texas, United States (US) (Karnae, 2005);
Montreal, Canada (Joly et al., 2010), and New Delhi, India,
(Mönkkönen et al., 2004). Firework emissions from at least
19 studies have also been linked to exceedance of the 24 h US NAAQS
limit for PM2.5 of 35 µg m-3 (Lin, 2016, and references therein). Higher PM concentrations from fireworks have been reported more
frequently in Asia (i.e., India, China, and Taiwan) compared to western
countries (Lin, 2016; Sarkar et al., 2010).
Health effects are of major concern during firework periods based on both
short- and long-term exposure. For example, Diwali is a major firework
festival in India, and it was shown that chronic exposure to three of the
most prominent tracer species (Sr, K, and Ba) translated to a 2 % increase
in health effects based on the non-carcinogenic hazard index (Sarkar et
al., 2010). On the other hand, short-term exposure to firework pollutants
increases asthma risk, eye allergies, cardiovascular and pulmonary issues,
cough, and fever (Moreno et al., 2010; Singh et al., 2019; Barman et al.,
2008; Becker et al., 2000; Beig et al., 2013; Hirai et al., 2000). Firework
pollutants also impact clouds and the hydrological cycle, owing to
associated aerosols serving as cloud condensation nuclei (CCN) (Drewnick
et al., 2006) and subsequently impacting surface ecosystems after wet
deposition (Wilkin et al., 2007). Although fireworks emit particles with
various sizes into the atmosphere, fine particles associated with PM2.5
are most relevant to public health effects, scattering efficiency, and CCN
activation (Vecchi et al., 2008; Perry, 1999). Knowing the various
effects of firework emissions depends on knowing their physical, chemical,
and optical properties.
Measurements of the chemical composition of firework emissions are important
in order to understand how they affect local air quality. The main
components of fireworks are fuels (metals and alloys, metalloids, and
non-metals), oxidizers (nitrates, perchlorates, and chlorates), and coloring
agents (metal salts) (Steinhauser and Klapotke, 2010). Previous studies
have relied on tracer species to establish confidence in distinguishing the
firework source from background air and other sources (Sarkar et al.,
2010). Potassium historically has been the most observable tracer for
fireworks emissions (Wang et al., 2007; Drewnick et al., 2006; Perry,
1999), with concentrations reaching 58 µg m-3 during the Diwali
festival in India (Kulshrestha et al., 2004). Firework color is created
by metal salts such as Sr for red, Ba for green, and Cu for blue-violet, all
three of which have been found to be effective tracers of fireworks
(Walsh et al., 2009; Vecchi et al., 2008). Strontium in particular is
an indicator of the spatial and temporal extent of firework smoke plumes
(Perry, 1999) because of the high prevalence of red in fireworks, and it
is not affected by traffic emissions (Moreno et al., 2010). Other
components measured in the air that have been attributed to fireworks
include metals (Al, Cd, Cu, Ti, Mg, Mn, Ni, Zn, As, Bi, Co, Ga, Hg, Cr, Pb,
Rb, Sb, P, Tl, Ag) and their salt anion counterparts (S, P, Cl). Thallium
makes a green flame. Potassium and Ag (as AgCNO or silver fulminate)
are propellants, Al is fuel, and Pb provides steady burn and is also used as
an igniter for firework explosions. Chromium is a catalyst for
propellants, Mg is a fuel, and Mg2+ is a neutralizer or oxygen donor
(U.S. Department of Labor, 2015). Manganese is either a fuel or
oxidizer, and Zn is used for sparks (Licudine et al., 2012;
Martín-Alberca and García-Ruiz, 2014; Shimizu, 1981; Wang et al.,
2007; Ennis and Shanley, 1991). Also from fuel and oxidizer combustion are
species such as NO3-, SO42-, and organics including
oxaloacetic acid (Alpert and Hopke, 1981; Barman et al., 2008; Carranza
et al., 2001; Dorado et al., 2001; Drewnick et al., 2006; Joly et al., 2010;
Joshi et al., 2016; Kulshrestha et al., 2004; Kumar et al., 2016; Lin et
al., 2016; Moreno et al., 2010; Sarkar et al., 2010; Tanda et al., 2019;
Thakur et al., 2010; Joshi et al., 2019). Firework-derived chloride in
Taiwan has been attributed to raw materials such as KClO3, ClO3,
and ClO4 with Cl-: Na+ ratios reaching approximately 3
(Tsai et al., 2012). Black carbon mass concentrations during firework
events can either increase due to firework emissions or decrease owing to
fewer vehicles on the road (Kumar et al., 2016; Yadav et al., 2019). In
both cases, the black carbon mass fraction decreases due to a greater
contribution of other constituents in firework emissions. Organic mass
concentrations and mass fractions have been noted to increase and decrease,
respectively, with fireworks (Zhang et al., 2019). Governed largely by
composition, particulate hygroscopicity and solubility have also been found
to be altered by fireworks depending on the emitted species. Inorganic salts
(K2SO4, KCl) dominated the aerosol hygroscopicity in Xi'an, China,
during fireworks (Wu et al., 2018). In the Netherlands, enhancements in
salt mixtures containing SO42-, Cl-, Mg2+, and K+
were noted to enhance hygroscopicity (ten Brink et al., 2018). Copper
and Mg were observed to become more soluble in firework emissions in Delhi,
India, while Mn, As, Ba, and Pb became less soluble (Perrino et al.,
2011). The water-soluble aerosol components from fireworks in the Sichuan Basin (China) were internally mixed and enhanced the hygroscopicity of
submicrometer aerosols, especially the larger particles (Yuan et al.,
2020).
In addition to composition, a necessary aspect of characterizing impacts of
firework emissions is to measure aerosol size distributions within the short
timeframe of an event (Joshi et al., 2019). Owing to combustion during
firework events, PM concentrations are dominated by particles in the
submicrometer range (Vecchi et al., 2008; Nicolás et al., 2009; Joshi
et al., 2019; Pirker et al., 2020; Do et al., 2012). Particle number
concentration maxima have been noted for the nucleation (0.01 to 0.02 µm) and Aitken (0.02 to 0.05 µm) modes (Yadav et al.,
2019; Yuan et al., 2020), in addition to both the small (0.1 to 0.5 µm) (Wehner et al., 2000; Zhang et al., 2010) and large (0.5 to 1.0 µm) ends of the accumulation mode (Vecchi et al., 2008) during
firework events. In Nanning, China, SO42- peaked at 0.62 µm
during fireworks (Li et al., 2017). The mass diameter of K+ was 0.7 µm due to firework emissions after transport in Washington state
(Perry, 1999). There are a few studies with observed particle mass
concentration increases in the coarser but still respirable (<10µm) mode (Tsai et al., 2011). In terms of dynamic behavior in the
size distributions, past work has shown a shift in number concentration from
nucleation and Aitken modes to the smaller end of the accumulation mode (0.1
to 0.5 µm), due to increased coagulation sinks (Zhang et al.,
2010). Finer-temporal-scale monitoring has revealed steep increases
in nucleation-mode and Aitken-mode particle concentrations associated with
firework emissions followed by a growth in accumulation-mode particle number
concentrations due to coagulation (Yadav et al., 2019). An opposite
shift to a smaller size distribution has been observed for certain species
(Mg, Al, Cu, Sr, and Ba) from the coarse mode to accumulation mode
(Tanda et al., 2019). Other work has shown that while there is usually a
quick drop in particle concentration to background values after firework
events (Joly et al., 2010), elevated number concentrations of
accumulation-mode particles are maintained for up to 3 h after peak
firework activity (Hussein et al., 2005). New particle formation events
with fireworks have also been reported in Mumbai, India (Joshi et al.,
2016), with enrichments of primary and secondary particles for up to 30 min after peak firework activity. Particle aging due to distance from
the source and meteorology alter firework emission particle concentrations
(Joly et al., 2010) and size distributions (Khaparde et al., 2012).
Meteorological and dynamic parameters such as wind speed, level of mixing
(turbulent kinetic energy), and mixing layer height (Lai and
Brimblecombe, 2020) influence peak concentration and composition of aerosols
after fireworks, as well as particle residence time in the atmosphere and
transport to nearby regions (Vecchi et al., 2008). Although firework
activities are episodic, their particulate emissions, especially in the
submicrometer mode (Do et al., 2012), reside in the atmosphere for as
long as several days to weeks (Liu et al., 1997; Lin et al., 2016; Kong
et al., 2015; Do et al., 2012). Dispersion of the particles under low wind
speed (1 m s-1) for particles between 0.4 and 1 µm is estimated
at 12 h (Vecchi et al., 2008) and can reach distances as far as a
hundred kilometers (Perry, 1999). Aitken-mode and larger particles are
dispersed by wind more than nucleation-mode particles (Agus et al.,
2008). Meteorological conditions, such as rainfall, can also decrease
firework particle loading in the air, and relative humidity can change the
hygroscopicity of firework emissions (Hussein et al., 2005), thereby
affecting their size and radiative properties.
Studies on aerosol properties are limited for the rapidly developing region
of Southeast Asia (Tsay et al., 2013). This compounds the challenge to
understand the interactions between aerosols and the complex
hydro-meteorological and geological environment in Southeast Asia
(Reid et al., 2013). Increased local and transported emissions
(Hopke et al., 2008; Oanh et al., 2006) in Southeast Asia add to the
complexity and affect air quality in the region. Firework emissions are an
example of extreme and regular local emissions in Southeast Asia. Even while
several studies exist in the neighboring regions of East Asia (e.g., China)
and South Asia (e.g., India), there currently is no in-depth analysis of the
chemical, physical, and optical properties of firework emissions in a
Southeast Asian megacity where fireworks are culturally significant (Dela
Piedra, 2018). This study is additionally novel because it includes
the following combination of data types to investigate fireworks:
size-resolved measurements (ionic/elemental composition, morphology),
vertically resolved data from a high-spectral-resolution lidar (HSRL),
PM2.5, and meteorology. This work reports these data during the 2019
New Year celebrations in Metro Manila, Philippines, one of the most
populated cities, with a population of 12.88 million (PSA, 2015). We address the
following questions in order. (i) What are the conditions of the atmosphere
during the study period in relation to aerosols, and how are these affected
by firework emissions? (ii) What are the concentrations, mass size
distributions, and morphological characteristics of different elemental and
ionic species specific to fireworks, and how do these affect bulk aerosol
hygroscopicity? The results of this work provide new data that can help
address how past and ongoing firework emissions impact health, visibility,
regional air quality, and biogeochemical cycling of nutrients and
contaminants in the Philippines, Southeast Asia, and, more broadly, for all
other cities with major firework events. It also contributes to the
growing body of firework research findings (Devara et al., 2015).
MethodsHourly PM<inline-formula><mml:math id="M54" display="inline"><mml:msub><mml:mi/><mml:mn mathvariant="normal">2.5</mml:mn></mml:msub></mml:math></inline-formula> mass concentration
Hourly PM2.5 mass concentrations were obtained to assess the evolution
of and the temporal characteristics of fine particulates due to fireworks
and their relation to meteorology and aerosol optical properties. The hourly
PM2.5 mass concentrations were collected at the Manila
Observatory, Quezon City, Philippines (14.64∘ N, 121.08∘ E, ∼70 m a.s.l.) (Fig. S1), with a beta attenuation monitor
(DKK-TOA Corporation) as part of the Acid Deposition Monitoring
Network in East Asia (EANET) (Totsuka et al., 2005). The beta attenuation monitor
collects PM2.5 samples on a ribbon filter, which are irradiated with
beta particles. The attenuation of the beta particles through the sample and
the filter is exponentially proportional to the mass loading on the
filter. These hourly data were then averaged over 48 h periods
coinciding with water-soluble aerosol composition measurements (Sect. 2.5)
before, during, and after the firework event.
Meteorological data
Rainfall, temperature, relative humidity, and wind data were collected at
the Manila Observatory with a Davis Vantage Pro2 Plus weather station
(∼90 m a.s.l.) before, during, and after the firework
period. Hourly precipitation accumulation and 10 min averaged temperature,
relative humidity, and wind were used for the analysis.
Back trajectories
Three-day back trajectories with 6 h resolution were generated using
the National Oceanic and Atmospheric Administration's (NOAA) Hybrid
Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) model (Rolph
et al., 2017; Stein et al., 2015) using the Global Data Assimilation System
(GDAS) with a resolution of 1∘ and vertical wind setting of
“model vertical velocity”. To ascertain the impact of fireworks on surface
particulate concentrations, back trajectories were chosen to end at the
beginning times of the sampling periods before, during, and after the
firework event. Trajectories were computed for an end point being at the
Manila Observatory at an altitude of 500 m because it represents the mixed
layer as done in other works examining surface air quality (Mora et al.,
2017; Aldhaif et al., 2020; Crosbie et al., 2014; Schlosser et al., 2017).
Remote sensing
Vertical profiles of aerosol backscatter cross section measured with the
University of Wisconsin high-spectral-resolution lidar (HSRL), which was
deployed at the Manila Observatory in support of CAMP2EX. The HSRL
instrument transmitting laser (Table S1) operates at 532 nm with 250 mW
average power and pulse repetition rate of 4 kHz. The HSRL technique
measures and separates the returned signal into the molecular and aerosol
backscatter by using a beam splitter and an iodine absorption cell filter.
The separated molecular signal allows for optical depth and backscatter
cross section measurements in contrast to a standard backscatter lidar that
requires assumption related to the particulate lidar ratio (Razenkov,
2010). The HSRL also measures the particulate depolarization ratio, an indicator
of aerosol or cloud particle shape with low depolarization indicative of
spherical particles, while intermediate values (10 %) indicate a mix of
spherical and nonspherical particles
(Burton
et al., 2014; Reid et al., 2017). HSRL data were uploaded and processed at
the University of Wisconsin–Madison Space Science and Engineering Center
server for periods before, during, and after the fireworks.
To verify the height values based on the vertical profiles of aerosol
backscatter, the surface-attached aerosol layer height is estimated
using the maximum variance method more commonly used for daytime convective
boundary layer detection (Hooper and Eloranta, 1986). The height
detection method is limited by the complexity of the firework event case
due, however, to pertinent rain signals. The surface-attached aerosol
layer is derived from a 15 min moving window average based on the 30 s
values.
Aerosol composition and morphology measurements
Size-speciated PM (cut-point diameters: 18, 10, 5.6, 3.2, 1.8, 1.0, 0.56,
0.32, 0.18, 0.10, and 0.056 µm) was collected on Teflon substrates
(PTFE membrane, 2 µm pores, 46.2 mm diameter, Whatman) with two
Micro-Orifice Uniform Deposition Impactor (MOUDI II 120R, MSP Corporation)
(Marple et al., 2014) samplers from the third floor of the main building
(∼85 m a.s.l.) at the Manila Observatory. Sample collection
for each of the three MOUDI sets lasted 48 h before (13:30 on 24 December 2018 to 13:30 on 26 December 2018), during (14:45 on 31 December 2018 to 14:45 on
2 January 2019), and after (13:30 on 1 January 2019 to 13:30 on 3 January 2019)
firework activities. Note that all times refer to local time (UTC+8).
Although there were no fireworks released from the sampling site, there was
firework activity in the immediate vicinity (∼500 m from the
sampling in all directions and all throughout the city in general). Firework
activity around the sampling site began around ∼ 19:00 on 31 December 2018, peaked at 00:00 of 1 January 2019, and dropped drastically
after. Based on PM2.5 data there was no evidence of sustained
firework activity past midnight. MOUDI samples collected before (24
to 26 December) and after (1 to 3 January) the firework event (31 December to 2 January) were considered as background samples. Although there is some firework
activity that is expected in the evening of 24 December (before the firework
event), this is minimal compared to that which is the focus of this study
(Dela Piedra, 2018; Santos et al., 2010; Roca et al., 2015). The
samples were covered with aluminum foil, sealed, and stored in the freezer
before being shipped to the University of Arizona for elemental and ionic
analysis.
Each sample substrate was cut in half. One half of each sample was extracted
in 8 mL Milli-Q water (18.2 MΩcm), sonicated, and analyzed for ions
(ion chromatography (IC): Thermo Scientific Dionex ICS-2100 system) and
elements (triple quadrupole inductively coupled plasma mass spectrometer:
ICP-QQQ; Agilent 8800 Series). The remaining substrate halves were stored.
Sample ionic and elemental concentrations were corrected by subtracting
concentrations from background control samples. More information about the
sampling and analysis is detailed in recent work (Stahl et al.,
2020b). Limits of detection of the 41 reported species are
summarized in Table S3. Potassium (K+) was reported based on ICP-QQQ
measurements rather than IC due to possible contamination from the KOH
eluent used in the latter instrument. Non-sea-salt SO42- was
calculated by subtracting 0.2517 × Na+ from the total SO42-
concentration (Prospero et al., 2003).
High-resolution scanning electron microscopy (SEM) combined with energy
dispersive X-ray analysis (EDX) was used for examining particle morphology
and chemical composition on a portion of the substrates collected during the
firework event. Analyses were performed with a Hitachi S-4800
high-resolution SEM and a Thermo Fisher Scientific Noran Six X-ray
Microanalysis System in the Kuiper Imaging cores at the University of
Arizona. Approximately 1 cm2 was cut from the center of substrate
halves and placed on double-sided carbon tape mounted on an aluminum stub. A
thin layer (1.38 nm) of carbon was coated on the sample surface using a
Leica EM ACE600 sputter coater to improve the sample's conductivity. SEM
images were obtained at 15 and 30 keV acceleration voltages and with a
20 µA probe current in high-magnification mode. The percentage
contributions and the spatial distribution of the elements were obtained
from the EDX analysis. Carbon, F, and Al should be ignored in the discussion
of SEM-EDX results since C and F are present in the Teflon substrates, and
the sample stub is an Al-rich substrate.
A total of 41 water-soluble species were detected in the 48 h
size-differentiated particulate samples collected before, during, and
after the firework event. The total bulk mass concentration is defined as
the sum of the concentrations of all the measured species across MOUDI's
11 stages (≥0.056µm).
Enrichment factor calculations
To identify which species are most enhanced during fireworks, enrichment
values are typically calculated using speciated concentrations during the
fireworks relative to baseline periods (Tanda et al., 2019). We
calculate water-soluble mass enrichment factors for each of the 41
measured species by dividing their total bulk (≥0.056µm) mass
concentrations during the firework event by the average of the total mass
concentration of the species measured before and after the firework
event. Size-resolved enrichments were similarly calculated using
measured mass concentrations for individual MOUDI stages. In a case when the
mass concentration of a species during the firework event was non-zero but
the mass concentrations during and after were zero (e.g., succinate), half
of the detection limit was used in place of zero values.
Hygroscopicity calculations
Hygroscopicity was calculated for particles ranging in size between 0.056–3.2 µm before, during, and after the firework event. This size range
was chosen to most closely be aligned with separate measurements of
PM2.5 in the study (Sect. 2.1) that were used to account for the
remaining mass not speciated in this study. We specifically calculate values
for the single hygroscopicity parameter kappa, κ (Petters and
Kreidenweis, 2007).
The water-soluble compound mass concentrations before, during, and after the
firework event were calculated using an ion-pairing scheme (Gysel et
al., 2007) for each MOUDI stage between diameters of 0.056 and 3.2 µm
and then summed to achieve a total mass concentration for each compound in
this size range. Black carbon mass concentrations in PM2.5 before and
after the firework event were calculated based on their long-term
(2001–2007) average contribution (32 %) to PM2.5 mass in December and
January (Cohen et al., 2009). Black carbon or elemental carbon (EC)
concentrations during the firework event were assumed to be the average of
the black carbon concentrations before and after the firework event. This
was done because black carbon concentrations have been observed to not
increase (Santos et al., 2007) as much as organic carbon (OC) (Lin,
2016), such that OC : EC mass ratios during fireworks have been observed to
increase. Total non-water-soluble content between 0.056 and 3.2 µm was
calculated as the difference between the total PM2.5 mass concentration
and the sum of the water-soluble species and black carbon mass
concentrations. The mass of each species was divided by its density, and
each of these volumes were added to quantify the volume of the measured
aerosol (water-soluble compounds, black carbon, and organic matter) between
0.056 and 3.2 µm. Volume fractions were then computed for each species.
The Zdanovskii, Stokes, and Robinson (ZSR) mixing rule (Stokes and
Robinson, 1966) was used to obtain the total hygroscopicity (total κ) of the mixed aerosols by weighting κ values for the individual
non-interacting compounds by their respective volume fractions and summing
linearly. Densities and κ values for the individual compounds are
based on those used elsewhere (AzadiAghdam et al., 2019), repeated in
Table S4.
Results and discussionHourly PM<inline-formula><mml:math id="M96" display="inline"><mml:msub><mml:mi/><mml:mn mathvariant="normal">2.5</mml:mn></mml:msub></mml:math></inline-formula>, meteorological, and transport patterns
We begin with hourly PM2.5 mass concentration results for the study
period to provide context for the spatiotemporal characteristics of fine
particulates due to fireworks, their interaction with meteorology, and
effects on aerosol optical properties. Hourly PM2.5 (Fig. 1) began to
increase from 44.0 µg m-3 (shortly after rising above the 24 h
Philippine Provisional National Ambient Air Quality Guideline Values (NAAQGV) of 50.0 µg m-3) after 18:00 on 31 December 2018 with the beginning of
firework activity and calm meteorological conditions. There was
moderate (3 mm) rainfall from 22:00 to 23:00 that night as the firework
activity began to increase. Rain is a sink for particles (Perry,
1999) and could have washed out some of the particulates in the air, thus
potentially causing a slight dip in the hourly PM2.5 around midnight.
PM2.5 peaked at 383.9 µg m-3 between 01:00 and 02:00 on 1 January 2019. The PM2.5 peak was delayed by approximately an hour from
the peak firework activity at midnight possibly due to rainfall, relative
humidity, and wind (Vecchi et al., 2008), in addition to aerosol
dynamical processes requiring time for secondary aerosol formation and
growth (Li et al., 2017). Minimal rain (0.2 mm in an hour) with high
relative humidity (between 93 % ± 4 % to 94 % ± 4 %) was conducive to aerosol growth and/or secondary particle formation. High relative humidity is related to aqueous-phase oxidation of SO2 (Sun et al., 2013) and NO2 (Cheng et al., 2014) as well as
metal-catalyzed heterogeneous reactions (Wang et al., 2007) to form
SO42-. Aqueous oxidation has been found to be a predominant
mechanism for the secondary formation of SO42- during fireworks
(Li et al., 2017), in addition to promoting secondary organic aerosol
formation (Wonaschuetz et al., 2012; Youn et al., 2013). Light wind
(∼1 m s-1) after midnight from the northeast could also
have transported more emissions from the populated Marikina Valley, located
in the northeast, to the Manila Observatory, contributing to the delay of the
PM2.5 peak.
(a) PM2.5 mass concentrations and rain accumulation
at hourly resolution (the time shown is local time (UTC+8); dashed vertical line indicates midnight)
as measured from the Manila Observatory main building third floor rooftop
(∼88 m a.s.l.) at the same period as the MOUDI size-speciated
samples during the firework event. Ten-minute-averaged values of (b)
temperature and relative humidity, in addition to (c) wind speed and
direction. The wind barb legend in panel (c) shows how flags are added to
the staff with increasing wind speed and in the direction where the wind
comes from. Figures S2 and S3 show the hourly PM2.5 mass concentrations
and 10 min meteorological data before and after the firework event,
respectively.
Particulate levels were enhanced for approximately 14 h from the beginning
of the firework activity (Fig. 1) during which the average PM2.5 (143.4 µg m-3) exceeded the 24 h Philippine NAAQGV between 18:00 on 31 December 2018 and 08:00 on 1 January 2019. After 02:00 on 1 January 2019,
PM2.5 dropped quickly to 122.0 µg m-3 between 03:00 and
04:00 (Fig. 1). The PM2.5 decrease was less pronounced after
04:00 but continued decreasing steadily along with slight rain (0.4 mm in an
hour) and light breeze (1–2 m s-1) from the northwest to southwest
directions. Firework activity in other countries has been documented to
last from 2–6 h in a day, and elevated particulate levels can be
maintained for up to 6–18 h (Thakur et al., 2010; Crespo et al., 2012;
Chatterjee et al., 2013; Kong et al., 2015; Tsai et al., 2012). The 48 h
average PM2.5 during (49.9 µg m-3) the firework event was 1.9
and 3.3 times more, respectively, than before (25.8 µg m-3) (Fig. S2) and after (15.2 µg m-3) (Fig. S3) the firework event. Increases in PM mass concentration of 2- to
3-folds due to fireworks have also been observed in other countries (Rao et al., 2012; Ravindra et al.,
2003; Tsai et al., 2011; Shen et al., 2009). Greater increases (>5 times) in particulate mass concentrations elsewhere were related to more
intense and prolonged (lasting several days) firework activity (Tian et
al., 2014).
Three-day back trajectories for the period before the firework event were
from the northeast to east directions coming from the Philippine Sea (Fig. 2a). For the periods (Fig. 2b) during and (Fig. 2c) after the
firework event, back trajectories were from the northeast to east/northeast
directions. The general wind directions from the back trajectories are
consistent with the climatologically prevailing northeasterly monsoonal
winds in December and January for the Philippines (Villafuerte et
al., 2014). The origin of the air parcels did not have any major emission
events that could have impacted the measurements after long-range
transport. This is important to note because the tracers for
fireworks are also tracers for transported emissions due to biomass burning
(K+) (Braun et al., 2020) and industrial activities (Cohen et
al., 2009). Thus, enriched particulate concentrations during the firework
activity were most likely locally produced. One factor impacting surface PM
concentrations is the vertical structure of the lower troposphere, which is
addressed in the next section based on HSRL data.
Three-day back trajectories with 6 h resolution
for the periods (a) before, (b) during, and (c) after the firework event,
ending at the point of the Manila Observatory at 500 m.
Optical aerosol properties
Heavy aerosol loading at the surface was observed up to 8 h after
the fireworks peak (00:00) with high HSRL 532 nm backscatter cross section
and depolarization (Fig. 3a) reaching ∼440 m above the
ground. Prior to the firework peak, the surface aerosol layer had
lower backscatter (before 22:00, Fig. 3a), and this cleaner condition is
shown by the 16:16 local time vertical profile of the aerosol backscatter
(Fig. 3b). Rainfall (Fig. 1a) contributed to columns of high backscatter
(Fig. 3a) after 22:00 and before the firework peak with a measurable
decrease in the aerosol backscatter for a short time after the precipitation
(23:00 and 00:00).
As confirmed by height detection, aerosols reached up to ∼440 m (Fig. 3a and b) at 00:00 (1 January 2019). It persisted for at least an
hour and then dropped to 118 ± 20 m with higher aerosol backscatter
retained until 1 January 2019 08:00. Some of the smoke is above the
detected height (i.e., 01:00).
(a) Time series of the aerosol backscatter vertical
profile from the high-spectral-resolution lidar (HSRL). The time shown is local time (UTC+8) at the Manila Observatory. The times circled by
the white oval correspond to the peak of aerosol backscatter in the mixing
layer due to firework activity. The approximate surface-attached aerosol
layer height is shown as a thick black line. It is derived from a 30 min
moving window average based on the 1 min values shown as a thin black line. (b)
Vertical profiles of aerosol backscatter at specific UTC times of interest
before, during, and after the fireworks.
Mass size distributions
Building on the previous results describing the general environmental
conditions during the study period, now we focus on the detailed
size-resolved measurements. The total water-soluble bulk mass concentration
(Table 1) during the firework event (16.74 µg m-3) was 5.71 times
and 4.73 times higher than the total bulk mass concentrations before (2.93 µg m-3) and after (3.54 µg m-3) the firework event,
respectively. Assuming the average of the water-soluble mass concentrations
before and after the firework event represents background values, this
translates to an 80.66 % increase in water-soluble mass during the
firework event.
Summary of total and speciated concentrations before,
during, and after the firework event. Species are divided based on units
(total to Zn: µg m-3; succinate to Se: ng m-3).
Total concentration Total concentration SpeciesBeforeDuringAfterSpeciesBeforeDuringAfterTOTAL2.9316.743.54MSA4.443.222.43nss-SO42-0.736.810.66Mn0.882.971.03K+0.375.050.25Rb0.621.240.25NO3-0.641.700.65Cr0.161.010.29Cl-0.231.460.57As0.600.710.38Mg2+0.060.370.10Ni0.410.460.99Na+0.330.330.53Ti0.100.270.24Ca2+0.210.300.38V0.320.140.30NH4+0.210.190.28Mo0.050.100.06Ba0.010.170.01Cd0.110.100.13Oxalate0.100.120.06Co0.050.050.05Cu2.48×10-040.071.86×10-03Cs0.020.020.01Al4.53×10-030.050.01Ag0.020.024.00×10-04Sr1.27×10-030.052.54×10-03Tl0.010.021.80×10-03Zn0.010.020.01Zr0.010.010.03Succinate0.989.510Sn0.016.69×10-040.03Pb1.688.331.03Y2.16×10-044.56×10-042.44×10-03Phthalate12.825.365.59Nb2.28×10-041.59×10-043.00×10-04Adipate5.354.8311.73Hf002.18×10-04Maleate1.544.120Hg1.03×10-0300Fe2.913.477.32Se5.7600
The firework event was associated with increased total water-soluble mass
fraction (32.33 %) (0.056–3.2 µm size range, Sect. 3.1) in
PM2.5 (Fig. S4) compared to before (9.90 %) and after (17.79 %) the
firework event. The water-soluble particulate mass fraction in PM2.5
similarly increased in other firework events (Yang et al., 2014). The
highest total water-soluble mass concentrations during the firework event
were from the following ions: non-sea-salt (nss) SO42- (6.81 µg m-3), K+ (5.05 µg m-3), NO3- (1.70 µg m-3), Cl- (1.46 µg m-3), Mg2+ (0.37 µg m-3), Na+ (0.33 µg m-3), and Ca2+ (0.30 µg m-3). These contributed to 95.75 % of the total detected bulk
water-soluble mass concentration then.
Total water-soluble bulk mass concentration during the firework event was
dominated by submicrometer particles, which accounted for 77.4 % of the
total water-soluble bulk mass (Fig. 4b). Supermicrometer mass fractions were
greater before (Fig. 4a) and after (Fig. 4c) the firework event (43.7 %
and 57.5 % of the water-soluble bulk mass concentration) compared to
during the firework event (22.6 %). The increase in submicrometer mass
fractions is typical with firework emissions (Crespo et al., 2012; Do
et al., 2012). In New York, fireworks contributed to 77 % of PM1 due
to potassium salts and oxidized organic aerosol (Zhang et al., 2019).
Speciated mass size distributions of the major aerosol
constituents measured (a) before, (b) during, and (c) after the firework
event. Table 1 lists the bulk (≥0.056µm) mass
concentrations of these ions and elements, including those labeled here as
“others” (Ba, oxalate, Cu, Al, Sr, Zn, succinate, Pb, phthalate, adipate,
maleate, Fe, MSA, Mn, Rb, Cr, As, Ni, Ti, V, Mo, Cd, Co, Cs, Ag, Tl, Zr, Sn,
Y, Nb, Hf, Hg, and Se).
Non-sea-salt SO42- had the highest contribution (40.7 %) to
total water-soluble bulk mass concentration during the firework event (Table 1). Sulfate exhibited a shift in its mass size distribution to a slightly
larger size during firework activity (Fig. 4b). During the firework event,
87.13 % of the nss-SO42- was in the 0.32 to 1.8 µm
size fraction. Before and after the firework event, 87.28 % and 85.14 %
of the nss-SO42- mass concentration, respectively, was distributed
in a finer size fraction (0.18 to 1 µm) (Fig. 4a and c).
Potassium contributed 30.19 % to the total water-soluble mass
concentration during the firework event (Table 1), presumably in the form of
KNO3. This compound is associated with black powder used as a
propellant (Li et al., 2017). Potassium's mass concentration
distribution similarly shifted to a slightly larger size during the firework
event (Fig. 4b). Most (87.6 %) of the bulk K+ mass concentration
during the firework event was between 0.32 and 1.8 µm, compared to
85.4 % and 79.4 % between 0.18 and 1 µm before and after the
firework event, respectively (Fig. 4a and c).
The shift in the mass size distribution of K+ and nss-SO42-
can be due to the removal of nucleation-mode particles as a result of
increased coagulation in the accumulation mode (Zhang et al., 2010).
Relatively larger SO42- particles can also be due to secondary
sources rather than primary sources, and aging could have also contributed
to particle growth as has been suggested for firework particles in Nanning,
China (Li et al., 2017). Firework emissions include gases like SO2
which undergo aqueous uptake and oxidation onto particles to form
SO42-. Furthermore, enhanced secondary formation is aided by
metals emitted during fireworks that help convert SO2 to
SO42- (Feng et al., 2012; Wang et al., 2007).
Nitrate, Cl-, and Mg2+ mass size distributions all exhibited
pronounced peaks in the submicrometer range during the firework event (Fig. 5). The mass sum concentration of the aforementioned ions peaked (46.39 %
of the total mass concentration of the three species) between 0.56 and 1.0 µm. On the other hand, their mode appeared between 1.8 and 3.2 µm
before and after the firework event (33.02 % and 32.91 % of the total
mass concentration of the three species, respectively) (Fig. 5). Nitrate, Cl-, and Mg2+ are emitted during fireworks (Zhang
et al., 2017) as finer-sized submicrometer particles (Tsai et al., 2011)
compared to background conditions when these species are mostly associated
with coarser supermicrometer particles (AzadiAghdam et al., 2019; Cruz et
al., 2019; Hilario et al., 2020). Nitrate can also be formed secondarily
(Yang et al., 2014) from firework emissions. Firework emissions are
associated with lower NO3-: SO42- ratios (Feng et
al., 2012) compared to days dominated by mobile sources (Arimoto et al.,
1996) due to different formation mechanisms (Tian et al., 2014).
Consistent with the literature, low NO3-: SO42 ratios
were also observed during the firework event (before: 0.79, during: 0.25,
after: 0.82). A low NO3-: SO42- ratio is related to
decreased pH of the particles (Cao et al., 2020), which may impact not
just air quality and health but also nearby waterbodies where the particles
may deposit. It is important to note that background supermicrometer
Cl- and Mg2+ in Manila are most likely associated with sea salt,
while background supermicrometer NO3- possibly in the form of
NaNO3 (de Leeuw et al., 2001) or NH4NO3 likely stems
from partitioning of nitric acid gas onto surfaces (de Leeuw et al.,
2001) of coarse particles such as sea salt and dust (AzadiAghdam et al.,
2019; Cruz et al., 2019). The Cl-: Na+ mass ratio during the
firework event increased to 4.44 (from 0.69 and 1.08 before and after,
respectively) and was higher than the typical Cl-: Na+ ratio in
seawater of 1.81 (Braun et al., 2017). These ratio results confirm that
the increase in Cl- concentrations during the firework event is not
driven by sea salt but instead linked to firework emissions. The lack of
increased sea salt influence during the firework event, which is not to be
expected, is further confirmed by relatively small changes in the amount of
observed Na+, as will be discussed subsequently.
Speciated mass size distributions before (blue line),
during (red line), and after (green line) the firework event. Next to
species labels are bulk (≥0.056µm) mass concentration
enrichment values due to the firework event; species are shown with
enrichments ≥1.9. Figure S5 shows similar results for all other
species.
The Na+, Ca2+, and NH4+ mass size distributions peak
in the supermicrometer range (1.8 to 3.2 µm) (Fig. S5), and total mass
concentrations (Table 1) varied minimally, relative to the earlier mentioned
species, before (0.33, 0.21, 0.21 µg m-3, respectively), during (0.33, 0.30, 0.19 µg m-3) and after (0.53,
0.38, 0.28 µg m-3) the firework event. The
minimal change in NH4+ mass concentration is most likely due to
little or no variation of its precursor gas (e.g., NH3) due to firework
activities and the fact that firework materials are commonly composed of
K-rich salts rather than NH4+ salts (Zhang et al., 2019). The
latter seems probable because the K : S mass ratios of 2.75 and 2.71, observed
from 0.18–0.32 µm and 0.32–0.56 µm, respectively, during the firework event suggest a firework-related source of K and S. This ratio is similar to the K : S ratio of 2.75 (Dutcher et al., 1999) of black powder (Perry, 1999), a type of pyrotechnic comprised of K and S.
The mass size distribution for the sum of the rest of the species
(“others” in Fig. 4) shifted from having a peak at the smaller end of the
accumulation mode (0.18–0.32 µm) before and after the firework event
to larger sizes in the accumulation mode (0.56–1.0 µm) during the
firework event. The shift in mode to slightly larger particles during the
firework event may be due to increased coagulation sinks (Zhang et al.,
2010) and secondary production (Retama et al., 2019). An additional
coarse peak (3.2–5.6 µm) observed after the firework event is mainly
attributed to sea salt constituents (e.g., Cl-, Na+) and likely
unrelated to firework emission aging and processing. The mass contribution
of the “others” to the total measured water-soluble mass concentration
decreased during the firework event to 4.3 % from 12.5 % before and
11.6 % after the firework event due to the prevalence of the ionic species
(nss-SO42-, K+, NO3-, Cl-, Mg2+,
Na+, Ca2+, and NH4+) discussed earlier (Table 1).
Enriched tracers in firework emissions
Here we more closely examine how much concentrations of species changed
during the firework event. Bulk mass concentrations of 18 of the
41 measured species were enriched during the firework event by more
than 2 times compared to the average of their bulk mass concentrations
before and after the firework event (Fig. 5). Enrichments for Cu (65.2), Sr
(24.4), succinate (19.4), Ba (18.2), K+ (16.3), nss-SO42- (9.8), Al (6.9), Pb (6.1), and maleate (5.3) were highest (>5)
among the species measured (Fig. 5). Potassium and nss-SO42-
together contributed to 70.9 % of the total measured species during the
firework event (Table 1). However, Cu, Sr, succinate, Ba, Al, Pb, and
maleate contributed a total of only 2.1 % to the total measured species
mass concentration. This reinforces the importance of looking at enrichments
rather than absolute mass concentrations for identifying which aerosol
constituents are firework tracers. Tracer metals in firework emissions were
previously shown to contribute a small fraction (∼<2 %) to total PM mass (Jiang et al., 2014).
Of the 18 species with observed enrichments exceeding two (Fig. 5),
only those which are firework components and that are uninfluenced by
secondary formation are considered tracers. The identified 14 firework
tracers based on these criteria are as follows: Cu, Sr, Ba, K+, Al, Pb,
Mg2+, Cr, Tl, Cl-, Mn, Rb, Zn, and Ag. Metals are usually in the
form of Cl- salts in fireworks (Wang et al., 2007). In this study,
the enrichment of Cl- during the firework event was found to be 3.7.
Some of the identified tracer metals are regulated, and their detection is of
concern. Magnesium is not recommended as a firework component because it is
sensitive to heat and can easily ignite in storage (Do et al., 2012).
Lead is highly toxic and thus regulated (Moreno et al., 2010) as its
occurrence in fireworks is a serious health hazard. Although
SO42-, maleate (fuel), and NO3- (oxidant) were also
enriched by more than 2 times during the firework event and are also firework
components (Zhang et al., 2019), they can be formed secondarily via
gas-to-particle conversion processes (Yang et al., 2014) and are not
considered as firework tracers. Succinate is likewise formed secondarily and
is not considered a firework tracer (Wang et al., 2007). The identified
firework tracers with the highest enrichments (>5) (excluding
K+), including Cu, Sr, Ba, Al, and Pb, together contributed 2.1 % to
the total measured species mass concentration during the firework event
(Table 1).
Size-resolved enrichments (Fig. 6) were highest in the submicrometer range
for most measured species. This is consistent with past studies such as in
Italy (Vecchi et al., 2008), Taiwan (Do et al., 2012), and Spain
(Crespo et al., 2012) where elemental concentrations due to pyrotechnics
increased in the submicrometer mode. The peak size-differentiated
enrichments of the first five firework tracers Sr (45.08), Ba (57.82),
K+ (48.70), Al (18.75), and Pb (69.07) were in the 1.0–1.8 µm
size range. Copper (49.85) peaked between 0.56–1.0 µm because
it did not have valid data for diameters exceeding 1.0 µm. Strontium
and Ba had very high enrichments (254.40 and 195.84) from 0.1–0.18 µm due to very low concentrations before and after the firework event in
that size range. Enrichments of up to ∼ 1000 (Crespo et
al., 2012) for Sr and Ba have been observed due to pyrotechnics, and both
are known firework tracers (Kong et al., 2015).
Size-resolved enrichments for individual firework tracer
species in order of decreasing total bulk mass concentration enrichment
(species from Fig. 5). Cut-point diameters with no valid data are left
blank. The y axis of Sr and Ba is truncated to more easily show enrichments
in the larger size fractions. Figure S6 shows similar results for all other
species.
The size-resolved enrichments of other notable species (Figs. 6 and S6)
peaked at specific size ranges between 0.32–1.8 µm: Mg2+
(18.93, 0.056–0.1 µm), Cr (14.37, 1.0–1.8 µm), Tl (18.12,
0.56–1.0 µm), Cl- (170.94, 0.32–0.56 µm), Mn (6.29,
1.0–1.8 µm), Rb (6.87, 1.0–1.8 µm), NO3- (7.26,
0.56–1.0 µm), Cs (6.28, 1.0–1.8 µm), Mo (4.15, 0.32–0.56 µm), Ti (6.63, 0.32–0.56 µm), Co (17.94, 0.56–1.0 µm),
and methanesulfonate (MSA) (6.66, 0.56–1.0 µm). Among all the
measured water-soluble species, Cl- had the highest size-resolved
enrichment, followed by Sr, Ba, K+, Pb, and Cu. This is expected
because inorganic salts comprise an enormous percentage of firework
emissions (Martín-Alberca et al., 2016).
SEM-EDX
In addition to size-resolved species concentrations, the morphology of
particles is important with regard to their optical properties,
hygroscopicity, and their transport behavior. Five SEM images from the
different stages (0.18–1 µm) of the MOUDI sampler with possible
firework influence are highlighted (Fig. 7). There were signs of nanoscale
aggregation that were chain-like and reminiscent of soot particles from
pyrolysis and combustion (Pirker et al., 2020; Pósfai et al., 2003;
D'Anna and Sirignano, 2015) in all of the images, and especially distinct in the 0.1–0.18 µm (Fig. 4b) and 0.18–0.32 µm (Fig. 7c) stages. Images for
larger sizes revealed relatively larger particles appearing as a translucent
crystal-shaped rectangle in the 0.32–0.56 µm image (Fig. 7d), in
addition to a capsule-shaped particle (Fig. 7e) and a cubic–shaped particle
(Fig. 7f) in the two 0.56–1.0 µm images. The presence of such
non-spherical shapes including chain aggregates points to the potential for
particle collapse and shrinking associated with humidified conditions as
noted in past work (Shingler et al., 2016, and references therein).
Scanning electron microscope (SEM) images of (a) a blank
PTFE (Teflon) substrate and (b–f) particles in different diameter ranges
with firework influence: (b) 0.1–0.18 µm, (c) 0.18–0.32 µm,
(d) 0.32–0.56 µm, and (e–f) 0.56–1.0 µm.
The chemical composition of the blank Teflon substrate (Fig. 7a) was
examined first by EDX to determine the background signals before the actual
samples were analyzed. The color intensity of the element maps (Fig. S7)
relates the concentration of the analyzed element relative to the
backscattered electron image (grayscale) of the sample. The background
substrate was dominated by C, F, and Al (bright yellow, bright blue, and
bright blue-green, respectively, in Fig. S7-a1/a2/a3). Metallic elements
were distributed in each of the five featured SEM images. Molybdenum and K
were present in all of the substrate stages (bright red in Fig. S7-b3/b4/c3/c8/d7/d8/e6/e7/f6/f9). Other metals were also found in the
different stages such as K, Mg, Al, Ru, Pd, Ba, Hf, and Tl. The identified
heavy metals in the particles are commonly used in firework as fuel
components, colorants, and oxidants (Singh et al., 2019). Potassium, Mg,
Al, Ba, and Tl are in the group of firework tracers that were already
identified (Sect. 3.4 and Fig. 5) to have mass bulk concentration
enrichments exceeding two. Molybdenum exhibited a reduced mass bulk
concentration enrichment of 1.93 (Fig. 5) but had size-resolved enrichments
between 1.21 and 4.15 (Fig. 6) in the substrate cutouts analyzed for EDX.
The cube-shaped feature in the 0.56–1.0 µm substrate appears to be
KCl because of the high color density of K and Cl in the elemental maps
(bright red and bright blue-green in Fig. S7-f6/f8) and because the shape of
KCl is cubic (Pirker et al., 2020). The crystal-shaped rectangle in the
0.32–0.56 µm range appears to be enriched by Cl (bright blue-green
in Fig. S7-d6). The same applies to the capsule-shaped particle in 0.56–1.0 µm image (bright blue-green in Fig. S7-e5). The chloride ion
(Cl-) is a component of metal salts, usually in the form of
ClO4- or ClO3- (Tian et al., 2014) used to color
fireworks (Shimizu, 1981).
These results of the sampled portions of the substrate stages are consistent
with the results of the size-resolved submicrometer enrichments measured by
IC and ICP-QQQ (Sect. 3.4) for Mo, K, Mg, Al, Ba, and Tl. Molybdenum was
brightest red in the 0.32–0.56 µm image (Fig. S7-d8), consistent
with the highest enrichments (4.15 in Fig. 6) for that size range. Potassium
was brightest red in the 0.56–1.0 µm image (Fig. S7-e6/f6),
consistent with highest enrichments (33.04 in Fig. 6). Magnesium was
brightest yellow from 0.32–1.0 µm (Fig. S7-d4/e3/f4), consistent
with highest enrichments (9.50 and 11.58 in Fig. 6). Aluminum had a high
signal in the blank Teflon substrate but also was brightest blue-green (Fig. S7-d5/e4/f5) in between 0.32–1.0 µm in the sample during the
firework event, consistent with highest enrichments (9.22 and 13.32 in Fig. 6). Barium was detected by EDX between 0.56–1.0 µm (Fig. S7-f11),
where its enrichment was 12.39 (Fig. 6). Thallium was detected between 0.56
and 1.0 µm (Fig. S7-f13) by EDX, where its enrichment was highest
(18.12 in Fig. 7) as detected by ICP-QQQ. The submicrometer metal salts due
to fireworks can uptake water at high humidity (ten Brink et al., 2018).
Hygroscopicity analysis
As fireworks alter the chemical profile of ambient PM, we estimate how
aerosol hygroscopicity responded during fireworks relative to periods before
and after. For reference, typical κ values range from 0.1 to 0.5 for
diverse air mass types such as urban, marine, biogenic, biomass burning, and
free troposphere (Dusek et al., 2010; Hersey et al., 2013; Shingler et
al., 2016; Shinozuka et al., 2009). AzadiAghdam et al. (2019) reported
size-resolved values ranging from 0.02 to 0.31 using data from the same
field site in Metro Manila but for a different time period and without any
firework influence (July–December 2018). They found the highest values to
be coincident with MOUDI stages with most sea salt influence (3.2–5.6 µm).
For this study, a bulk κ value is reported for the size range
between 0.056–3.2 µm as noted in Sect. 2.7, and subsequent
references to composition data are for this size range. Kappa was enhanced
during the firework event (0.18) compared to before (0.11), due mostly to
increased contributions from K2SO4 and Mg(NO3)2 (Fig. 8a). This is expected because based on the ZSR mixing rule (Stokes and
Robinson, 1966) the bulk hygroscopicity (κ) is dependent on the sum
of the κ values for individual non-interacting compounds weighted by
their respective volume fractions. More specifically, the volume fractions
of K2SO4 and Mg(NO3)2 increased from 0.01 to 0.10 and
0.01 to 0.03, respectively (Fig. 8b). Notable reductions in volume fraction
during the firework event were for NaNO3 (0.01 to 0.00), black
carbon (0.26 to 0.12), and (NH4)2SO4 (0.02 to 0.01) (Fig. 8b). All
three species are not associated with primary firework emissions. Although
NaNO3 and (NH4)2SO4 are hygroscopic, their decreased
volume fractions happened alongside a decreased volume fraction of
non-hygroscopic black carbon and increased volume fractions of the
firework-related and hygroscopic K2SO4 and Mg(NO3)2,
which increased bulk aerosol hygroscopicity during the firework event.
(a) Kappa (κ) values for the aerosol fraction
between 0.056–3.2 µm before, during, and after the firework event.
The speciated contributions to the overall κ values (represented by
the colors) are categorized based on the classes of compounds in the legend
following past work (AzadiAghdam et al., 2019). Ammonium sulfate,
K2SO4, Mg(NO3)2, and NaNO3 are high κ
inorganics but are plotted separately because of their large contributions.
The speciated contributions were calculated by multiplying the (b) volume
fraction of each compound class by its intrinsic κ value (Table S4).
Kappa decreased to an intermediate value after the firework event (0.15)
(Fig. 8a); this value exceeds that from before the fireworks owing partly to
more sea salt influence that was unrelated to fireworks. The change in
volume fraction of sea salt from before and during fireworks (0.01) to after
the fireworks (0.03) (Fig. 8b) translated to an increase of 0.03 in bulk
κ (Fig. 8a) from before to after the firework event. Although
fireworks emit extensive amounts of inorganic species, the calculated
κ values were still relatively low because the background air is
dominated by organics and black carbon, which are relatively hydrophobic
species (Table S4) (Cohen et al., 2009; Oanh et al., 2006; Cruz et al.,
2019).
Conclusion
This study reports on important aerosol characteristics measured during the
2019 New Year fireworks in Metro Manila. Notable results of this work,
following the order of questions raised at the end of Sect. 1, are as
follows.
Firework activities caused significant enhancement of PM2.5, reaching a
maximum of 383.9 µg m-3 between 01:00 and 02:00 on 1 January 2019.
Surface aerosol loading increased over a period of 8 h during the
firework event, coincident with peak PM2.5 levels. The heaviest aerosol
layer measured by the HSRL lidar was observed for at least an hour and
reached ∼440 m above the surface, after which the aerosol
layer dropped to 118 ± 20 m. Aerosol backscatter during the firework
activity decreased noticeably for short periods after rainfall. Furthermore, rainfall, wind, and relative humidity also possibly contributed to washout,
local dispersion, and secondary formation of particles, respectively. There
was no significant influence from long-range transport to the sampling site,
confirming that the sample data were most representative of the local nature of particulate enhancements observed during the firework event.
The firework event enhanced bulk concentrations of water-soluble aerosol
species, especially in the submicrometer range. Mass size distributions of
the water-soluble species shifted to slightly larger accumulation-mode sizes
most likely due to increased coagulation sinks and secondary formation.
Potassium and nss-SO42- were the major water-soluble contributors.
Cubic and capsule-shaped Cl--rich particles were prominent in
submicrometer particles collected during the firework event, suggesting the
presence of KCl. Inorganic species including Cu, Sr, Ba, K+, Al, Pb,
Mg2+, Cr, Tl, Cl-, Mn, Rb, Zn, and Ag were enriched by more than 2 times by mass during the firework event as compared to before and after the
event. While the most enriched inorganic firework tracers, including Cu, Sr,
Ba, Al, and Pb (excluding K+), comprised only 2.1 % of the total
water-soluble mass, their contribution is significant because they support
findings that the samples represent firework emissions. The increased volume
fractions of inorganics increased aerosol hygroscopicity (κ) between
0.056 and 3.2 µm from 0.11 (before the fireworks) to 0.18 during the
firework event.
Fireworks caused unhealthy levels of PM2.5 that exceeded the Philippine
(50.0 µg m-3), US (35.0 µg m-3), and World Health
Organization (WHO, 25.0 µg m-3) standards for PM2.5 over 24 h. The brief but sharply enhanced concentrations of water-soluble
species in the submicrometer size range, especially for K+ and
SO42-, have implications for both public health and the
environment, the former of which is owing to how smaller particles can
penetrate more deeply into the human respiratory system. Some of the
components detected during the fireworks were submicrometer Pb and
Mg2+, which is of concern because these are banned substances due to
their being health and fire hazards, respectively. The presence of Pb in the
firework emissions exacerbates the presence of submicrometer Pb in Metro
Manila (Gonzalez et al., 2021). The results show the opportunity that
improved quality and management of fireworks can have for better local air
quality.
Higher concentrations of secondary particles in the accumulation mode from
fireworks are related to increased mass extinction efficiency and therefore
decreased visibility (Jiang et al., 2014), as was observed in this
study. The increased water-soluble fraction, especially in the submicrometer
mode, during firework events coincides with elevated particle
hygroscopicity, which is related to CCN activity (Drewnick et al., 2006)
at smaller diameters (Yuan et al., 2020), with implications that can be
better assessed in a future study. The atmospheric environment in Southeast
Asia, coupled with increasing emissions and extreme sources such as
fireworks, offers a unique field laboratory for the study of aerosol aqueous
processes.
Data availability
Size-resolved aerosols data collected at the
Manila Observatory can be found in Stahl et al. (2020a) on figshare at https://doi.org/10.6084/m9.figshare.11861859
as well as on the NASA data repository at https://doi.org/10.5067/Suborbital/CAMP2EX2018/DATA001 (NASA, 2020).
The supplement related to this article is available online at: https://doi.org/10.5194/acp-21-6155-2021-supplement.
Author contributions
MTC, MOC, JBS, RB, ABMD, CS, and AS designed the experiments. All coauthors
carried out various aspects of the data collection. MTC, ELE, SMV, RH, GL, LM,
CS, and AS conducted analysis and interpretation of the data. ELE, LM, SMV,
RH, GRL, and AS prepared the manuscript with contributions from the
coauthors.
Competing interests
The authors declare that they have no conflict of interest.
Special issue statement
This article is part of the special issue “Cloud Aerosol and Monsoon Processes Philippines Experiment (CAMP2Ex) (ACP/AMT inter-journal SI)”. It is not associated with a conference.
Acknowledgements
The authors acknowledge support from NASA grant 80NSSC18K0148 in support of
the NASA CAMP2Ex project. Rachel Braun acknowledges support from the
ARCS Foundation. Melliza Templonuevo Cruz acknowledges support from the Philippine
Department of Science and Technology's ASTHRD Program. Alexander B. MacDonald
acknowledges support from the Mexican National Council for Science and
Technology (CONACYT). We acknowledge Agilent Technologies for their support
and Shane Snyder's laboratories for ICP-QQQ data. We thank the Department of
Environment and Natural Resources Environmental Management Bureau (DENR-EMB)
Central Office Air Quality Management Section in the Philippines and the Air
Center for Air Pollution Research in Japan of EANET for the hourly
PM2.5 data. The tradition of sampling the New Year air quality in Metro
Manila was instilled by Dan McNamara, SJ, Jett Villarin, SJ, and
Gemma Narisma, and for this we are grateful.
Financial support
This research has been supported by the National Aeronautics and Space Administration (grant no. 80NSSC18K0148).
Review statement
This paper was edited by Tuukka Petäjä and reviewed by two anonymous referees.
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