the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Vertical profiles of volatile organic compounds and fine particles in atmospheric air by using aerial drone with miniaturized samplers and portable devices
Eka Dian Pusfitasari
Jose Ruiz-Jimenez
Aleksi Tiusanen
Markus Suuronen
Jesse Haataja
Juha Kangasluoma
Krista Luoma
Tuukka Petäjä
Matti Jussila
Marja-Liisa Riekkola
Abstract. The increase of volatile organic compounds (VOCs) emissions released into the atmosphere is one of the main threats to human health and climate. VOCs can adversely affect human life through their contribution to air pollution directly and indirectly by reacting via several mechanisms in the air to form secondary organic aerosols. In this study, aerial drone equipped with miniaturized air sampling systems including up to four solid-phase microextraction (SPME) Arrows and four in-tube extraction (ITEX) samplers for the collection of VOCs, along with portable devices for the real-time measurement of black carbon (BC) and total particle numbers at high altitudes was exploited. In total, 135 air samples were collected under optimal sampling conditions in October 2021 at the boreal forest SMEAR II Station, Finland. A total of 48 different VOCs, including nitrogen-containing compounds, alcohols, aldehydes, ketones, organic acids, and hydrocarbons, were detected at different altitudes from 50 to 400 m above ground level with the concentrations up to 6898 ng m-3 in gas phase and 8613 ng m-3 in particle phase. Clear differences in VOCs distribution were seen in samples collected from different altitudes, depending on the VOC sources. It was also possible to collect aerosol particles by the filter accessory attached on the ITEX sampling system, and five dicarboxylic acids were quantified with the concentrations of 0.43 to 10.9 µg m-3. The BC and total particle number measurements provided similar diurnal patterns, indicating their correlation. For spatial distribution, surprisingly the BC concentrations were increased at higher altitudes being 2278 ng m-3 at 100 m and 3909 ng m-3 at 400 m. The measurements onboard the drone provided insights into horizontal and vertical variability in BC and aerosol number concentrations above the boreal forest.
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Eka Dian Pusfitasari et al.
Status: final response (author comments only)
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RC1: 'Comment on acp-2023-40', Anonymous Referee #1, 18 Feb 2023
Review of “Vertical profiles of volatile organic compounds and fine particles in atmospheric air by using aerial drone with miniaturized samplers and portable devices” by Pusfitasari et al.
The authors presented a drone-based platform for VOC and PM sampling, as well as in-situ measurements of BC and PNC; the platform was also used to perform field measurements in forested environments to investigate the vertical distribution of speciated organic compounds in both gas and phase, in relation to the measured BC and PNC profiles. The methodology and measurement results presented here are of interest to readers of ACP. The study was well designed and fairly clearly presented. I recommend Minor Revision with a few comments as below.
Main:
- It is not very clear how particle-phase VOCs were sampled, using ITEX? And how does it differ from the aerosol-phase carboxylic acid sampling using filter accessory in another method?
- The authors presented gas-phase and particle-phase data separately in Figures 2-5. Is there a way to discuss more on how those VOCs partition between two phases? For instance, how do their partitioning coefficients depend on altitude and/or PM composition (BC or others).
- Are the measured vertical distribution and/or temporal distribution of the VOCs/carboxylic acids depending on 1) meteorological conditions (PBL height etc.); 2) oxidative conditions (O3 levels etc.); and 3) PM concentration and characteristics (BC or PNC)?
Minor:
- Figures 4-5: not sure why cumulative concentration is needed as an x-axis parameter.
- Figure 7: font size too small to see clearly.
- Figure 6: how come there is such large negative concentration of BC in Phase I of Figure 6 (left)?
Citation: https://doi.org/10.5194/acp-2023-40-RC1 -
RC2: 'Comment on acp-2023-40', Anonymous Referee #2, 08 Mar 2023
This manuscript investigates the vertical profiles of VOCs and fine particles using samplers onboard a UAV. The UAV was equipped with miniature SPME and ITEX samplers. The SPME sampler was mainly used for gas-phase sampling and the ITEX can be used for both gas and particle sampling. Clear vertical characteristics were observed for VOCs with different sources. Results show that the diurnal pattern of BC was similar to the pattern of particle number concentration, and the BC concentration increased with height from 50 m to 400 m. Overall, the results are interesting. However, I have some major concerns about the UAV VOC sampling methodologies and data interpretation.
- Line 24: Please provide the time period of the sampling.
- Lines 32-33: The measurement was conducted at a rural site over the forest. Was there any BC source around the site? If not, should BC concentration be lower at the surface and higher at the high altitude? Why the results are surprising? Please clarify.
- Lines 78-87: A brief introduction of the ITEX system is required.
- Line 94: Was aerosol collected by ITEX tube or by filter connected to the ITEX system? Please clarify.
- Section 2: A table summarizing the target chemical species and their sampling and detection (including the detection limit) techniques would be helpful for the readers to understand how different species were sampled and analyzed in this study. The current presentation of the manuscript is somewhat confusing. Both the gases and particles were collected and measured by several methods.
- Section 2.3: What was the influence of UAV propellers on VOC sampling? The sampling inlet was located underneath the UAV, under which circumstance, the sampling may be affected by UAV downwash. In addition, VOC was sampled during the descending flights. The air underneath UAV was consistently affected by the UAV propeller. Depending on the size and payload of UAV, this influence can be several 10s of meters. Then how could the sampling be representative at different heights, especially for the sampling protocols shown in Figures S1 and S4?
- Lines 151-153: If I understand correctly, the desorption processes took about 4 s (800 uL / 200 uL s-1). What were the desorption efficiency of different VOCs?
- Lines 190-191: Please provide the detection limit of GC-MS analysis for different VOCs. Somewhere in the manuscript, the total VOC sampling volume needs to be noted. The sampling flow rate was 40 to 78 mL/min, and the sampling took about 10 min according to Figures S1 to S4. So the sampling volume ranged from 400 mL to 780 mL. The concentrations of ambient VOCs ranged from a few 100s of ng m-3 to several 1000s of ng m-3 (e.g., Figure 2). In this case, the GC-MS must be very sensitive so that it could measure VOCs with such a small amount. Please clarify.
- Lines 227-234: Why PLSR was used for the quantification of VOC compounds? What do you mean by semi-quantification? Here list 19 standards for VOC quantification. What about the quantification of the other VOCs without standards?
- Line 261: Please provide the references of the “previous studies”.
- Line 262: The authors mentioned that “the average sampling time that is used before reaching equilibrium for both MCM-41-Arrow and DVB/PDMS-Arrow units is about 20 minutes”. However, the total sampling time was 10 min as shown in Figures S1 to S4. Please clarify.
- Figure 2: The measurement was taken over the forest. However, no information about the concentration of isoprene, monoterpenes, and sesquiterpenes was presented. Were these compounds detected? What were the concentrations of these compounds?
- Figure 3: It is difficult to believe that very volatile compounds such as benzene can present in the particle phase. Any explanation? In addition, was water vapor removed before VOC collection? How was the sampling affected by humidity, especially for the cases where a filter was presented in front of ITEX? Would water condensation increase the loss of VOCs on filter?
- Line 418: for “the first sampling system”, do you mean “ITEX (+ filter accessory)”?
- Lines 419-421: How was the recovery calculated?
- Figure S6: Please use the same color code for the left and the right panels. After correction of VOC losses onto the ITEX filter, do the ITEX and SPME methods provide identical results? If not, please provide the reasons.
- Section 3.5: It has been reported in the literature that there may be negative artifacts using filters to collect particles, since some of the semi-volatile organic compounds can evaporate from the filters. Please discuss this uncertainty for the filter sampling and analysis in the current study. (Reference: Xinghua Fan, Patrick K.H. Lee, Jeffrey R. Brook & Scott A. Mabury (2004) Improved Measurement of Seasonal and Diurnal Differences in the Carbonaceous Components of Urban Particulate Matter Using a Denuder-Based Air Sampler, Aerosol Science and Technology, 38:S2, 63-69, DOI: 10.1080/027868290504090)
- Figure 5: I don’t think that it is a good way to compare the concentration differences between the gas and the particle phases by adding up the results from different altitudes and different days. For example, the concentration distribution at 50 m was very different on Day 1 comparing to Day 3. Please remade the figure separating the results either by day or by altitude.
- Lines 494-495: The authors mentioned that “BTX (benzene, toluene, xylene) were mostly discovered at the altitude of 50 m.” BTX indicated the influence of the anthropogenic sources. This observation was different from that of BC, another anthropogenic tracer. Any explanation for this?
- Line 510: Change “m-3” to “m”
- Table 2: The comparison of BC concentrations observed at the listed different locations is meaningless since the landscape, emission source, and atmospheric condition are totally different among the locations. If the authors still want to make a comparison, why not just compare the BC concentration detected over the boreal forests?
- Figure 6: It is strange to put the altitude on the x-axis.
- Lines 582-585: I don’t think that the explanation for large BC variation is convincing. The boundary layer stratification and turbulence could affect both BC and particle number concentration measured by CPC. In addition, what was the temperature variation during the measurements when the UAV was hovering? It is hard to believe that the change in temperature would be so significant to affect BC measurement when hovering.
Citation: https://doi.org/10.5194/acp-2023-40-RC2
Eka Dian Pusfitasari et al.
Eka Dian Pusfitasari et al.
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