the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Secondary Aerosol Formation in Incense Burning Particles by Ozonolysis and Photochemical Oxidation
Zhancong Liang
Liyuan Zhou
Xinyue Li
Rosemarie Ann Infante Cuevas
Rongzhi Tang
Mei Li
Chunlei Cheng
Yangxi Chu
Abstract. Incense burning is a common religious activity that emits abundant gaseous and particulate pollutants into the atmosphere. During their atmospheric lifetime, these gases and particles are subjected to (photo-)oxidation, leading to the formation of secondary pollutants. We examined the oxidation of incense burning plumes under O3 exposure and dark condition using an oxidation flow reactor connected to a single particle aerosol mass spectrometer (SPAMS). Nitrate formation was observed in incense burning particles, mainly attributable to the ozonolysis of nitrogen-containing organic compounds. With UV on, nitrate formation was significantly enhanced, likely due to HNO3/HNO2/NOx uptake triggered by OH chemistry, which is more effective than ozone oxidation. The extent of nitrate formation is insensitive to O3 and OH exposure, which can be explained by the diffusion limitation on interfacial uptake. The OH-aged particles are more oxygenated and functionalized than O3-aged particles. Oxalate and malonate, two typical secondary organic aerosols (SOA), were found in OH-aged particles. Our work reveals that nitrate, accompanied by SOA, can rapidly form in incense-burning particles upon photochemical oxidation in the atmosphere, which could deepen our understanding of air pollution caused by religious activities.
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Zhancong Liang et al.
Interactive discussion
Status: closed
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RC1: 'Anonymous review of “Secondary Aerosol Formation in Incense Burning Particles by Ozonolysis and Photochemical Oxidation” for Atmos. Chem. Phys.', Anonymous Referee #1, 09 Jan 2023
General Comments
Liang et al. (manuscript) describes the experimental formation of SOA and nitrate through chemical aging induced in an oxidation flow reactor (OFR). The authors injected combustion air from incense burning into the OFR at high RH, which were rapidly aged by controlling UV light and O3 to mimic UV-aged, O3-aged, and OH-aged scenarios. The authors used a single-particle AMS (SPAMS) to obtain the chemical composition of the particles and the Gothenburg PAM OFR (Go:PAM) as the reaction vessel.
The authors use the adaptive resonance theory method (ART-2a) algorithm to perform cluster/categorization analysis with the mass spectra (Zhao et al., 2008). The authors conclude that the OH-aged case generates more secondary nitrate than the O3-aged case based on the higher relative peak area (RPA). The enhanced secondary nitrate formation is attributed to higher uptake of nitrogen-containing species.
The manuscript overall lacks quantitative information, and I am confused about the OFR configuration. The authors provide some [NOx] information in Figure S10 and in the text, but a NOx instrument is not shown in the OFR set up in Figure S1. Moreover, the flow rates entering and exiting the OFR in Figure S1 already match, so adding a NOx monitor would cause a flow imbalance.
Moreover, the methodology and instrument details are lacking for replication, and additional explanations are needed to connect the chemistry in these OFR conditions to those of the atmosphere. For instance, the manuscript is missing the Go:PAM temperature and experiment residence times. The generated particle number concentrations from the WCPC, the particle mass collected on the filters for IC analysis, and the mass of incense used are not available. I do not have a clear picture of how much aerosol entered and exited the OFR.
The experiments and discussions fall within the scope of Atmos. Chem. Phys., and the content is topical to the atmospheric chemistry community. However, the manuscript is currently underprepared for publication, and there are technical issues that need resolution. Given the importance of understanding how chemical aging impacts aerosol evolution, I request the authors perform major revisions and resubmit the manuscript.
Specific Comments
1. The SPAMS calibration is not outlined, and details on the ART-2a solution is inadequate.
Details on the SPAMS operation would help assess the data quality. The Aerodyne soot particle AMS requires laser alignments for consistent measurements (Avery et al., 2020); does the SPAMS in this manuscript need a similar calibration? Particle transmission through the aerodynamic lens is size-dependent (Huang et al., 2013). How would size-dependent particle detection influence the data interpretation?The absolute peak area (APA), relative peak area RPA, and number fraction (NF) are frequently invoked in the data interpretation. The authors use APA and RPA as analogues to concentration (or fraction of total aerosol). However, I suspect that depends on how efficiently different species are ionized by the pulsed Nd:YAG laser, and I would like to know if adjustments have been made to the RPA based on the ionization efficiency. What is the ionization efficiency (IE) of species mentioned in the manuscript, and is IE consistent across species?
As for the ART-2a solution, Zhao et al. (2008) and Huang et al. (2013) note that there is no general rule for the vigilance factor, and that a comparative approach (like re-grouping or comparing with other clustering algorithms) may be needed. I also note there is no PAH category, despite particulate PAH found in previous incense combustion studies (Ji et al., 2010) and a PAH contribution being found in a similar mass spectrometer with ART-2a (Passig et al., 2022). Can the authors provide more detail and justification for their ART-2a solution?
2. OFR characterization and operation details are missing.
Offline OHexp calibrations may be inaccurate when OH reactive species suppressed OH. Basically, OH suppression is when the external OH reactivity (extOHR) entering the OFR is high enough to titrate the OH, which results in OH-aging being suppressed. In such scenarios, offline OHexp calibrations become unreliable, possibly by orders of magnitude (see Section 3.1.4 of Peng and Jimenez, 2020). Peng and Jimenez (2020) also notes that OFR254 is susceptible to OH suppression at low O3 injections.Operational information of the OFR would be valuable for replication and should be mentioned in the supplementary. Watne (2018) describes the Go:PAM as being made of quartz; have there been efforts to constrain electrostatic particle wall loss (Cao et al, 2020)? How would gas wall loss (Palm et al., 2016) affect the results reported, or is gas wall loss negligible? What cleaning procedure was taken to minimize carryover effects between experiments?
3. Kinetic modeling may be needed for interpretation.
The authors’ argument on secondary nitrate formation, either heterogeneously or in the gas phase is limited by the lack of quantification HNO3, HONO, NOx, NOy etc. The difference in condensed nitrate between the O3 and OH-aged cases may be due to differences in HNO3/HONO/NOx uptake as the authors allege. A kinetic calculation showing that the formation of these species under the difference OFR conditions are comparable would be more demonstrative.Moreover, gas-phase organic nitrate formation, either through VOC+NO3 or RO2+NO (Ziemann and Atkinson, 2012) and condensation should be considered. Kinetic modeling may be needed to connect the experimental aging conditions in the Go:PAM to those of the atmosphere (Peng and Jimenez, 2020).
Line 30: I recall incense burning is found in other cultures and am unsure if the practice is “especially” common in Asian and African religious rituals. I suggest either providing a reference for that point or removing “especially” in this sentence.
Line 35: The incense burning references cited here mention that there is variation in the particle emission factor (EF) across incense varieties. How does the particle EF in these experiments compare with those previous works? Were the combustion conditions comparable to those previous works?
Line 62: There is no information on the incense sticks used, like the manufacturer or composition, and Liang et al. (2022) used several as shown in their Figure S21. What type of incense was used here? How much incense was burned? This information could be valuable for replication studies.
Line 64: The methods reference (Liang et al., 2022) states there were four UVA lamps, while here the authors say they used “two UVC light tubes.” Please confirm that the Go-PAM set up had changed for this manuscript and specify that in the text. Moreover, what lamps were used? Rowe et al. (2020) found that 185 and 254 nm photon fluxes would vary across manufacturers, which may be re
Line 65: I am confused on how many experiments this manuscript is describing. I see in Figure 2 that there were 7 involving aging and 1 fresh; were some of these the “control” experiments? From this sentence I expect at least 2 types of controls, with either a charcoal absorber or HEPA filter. Were the control cases then also aged?
Line 66: How did the authors obtain these removal efficiencies?
Line 67: Compressed air or zero air? If the air is coming from a compressor, were efforts made to scrub the air of contaminants?
Line 74: The methods reference (Liang et al., 2022) does not mention using a diffusion dryer. At ~0.1 LPM, what was the residence time in the dryer and is there an estimate of particle loss in the dryer? Was the dryer effective in removing H2O?
Line 76: What were the estimated number of particles collected?
Line 83: Please provide additional details on the OHexp calibration with SO2, in particular the concentrations of SO2 used and timescales to reach equilibrium. An estimate of extOHR during the experiments should be compared with that of the SO2 calibrations.
Line 101: See specific comment 1.
Line 113: Explaining the abbreviations would improve readability. For instance, OC and ONEC do not appear prior in the text?
Line 147-149: How does the charcoal absorber remove NOx without removing VOC? How would the removal of VOC affect the interpretation here?
Line 156: How would the loss of SVOC/LVOC in the HEPA filter (Shilling, 1997) affect the conclusion of the control experiment?
Line 182: How did the authors arrive at the “~90 % reduction of [NOx]”? Was this a separate test? If so, please add a quick summary of how that test was performed.
Line 183: Was a NOx monitor available? If so, please provide the monitor’s location in Figure S1 and specify in the text. Also, please explain how the flow rates entering and exiting the Go:PAM would be reconciled.
Line 191-193: Do OH and O3 oxidation form similar functional groups? Are those functionalities evenly represented in these general markers? The RPA increase of SOA markers in OH over O3-aging may be skewed if these markers overrepresent one oxidation case over the other.
Line 214: Do larger and smaller particles have similar surface properties, at least with regards to nitrate uptake?
Line 222: I suspect SOA formation is not “potential,” but rather inevitable under the aforementioned OFR conditions, so I suggest removing “potential” from the section heading. Also, are oxalate and malonate universal and proportional indicators of SOA? That is, do different SOA precursors form these indicators evenly under different oxidants (O3/OH)? I am concerned that there are specific chemical conditions where these species are enhanced without a proportional enhancement of SOA, which may skew the NF.
Line 229: Is NF of oxalate and malonate proportional with SOA concentrations? As it stands, “30 and 9 folds” increases of these tracers sounds like SOA increased by that much.
Technical Comments
Line 47: Awkward grammar in “For instance … nitrate.”
Line 325: Please check the citation styles; they are inconsistent.
Lines 409/412: Same reference cited twice?
Figure 2: The data appears almost randomly scattered in the lower panels, which may be due to points heavily overlapping with each other. The authors may want to replace the box and whiskers/scatterplot with a violin plot for easier visualization.
Figure S1: Please display where the charcoal absorber, HEPA filter, and NOx instrument would have been placed.
References
Avery et al. (2020): https://doi.org/10.1080/02786826.2020.1844132
Cao et al. (2020): https://doi.org/10.1016/j.atmosenv.2019.117086
Huang et al. (2013): https://doi.org/10.1016/j.atmosenv.2012.09.044
Ji et al. (2010): https://doi.org/10.1111/j.1600-0668.2009.00634.x
Liang et al. (2022): https://doi.org/10.1021/acs.estlett.2c00492
Palm et al. (2016): https://doi.org/10.5194/acp-16-2943-2016
Passig et al. (2022): https://doi.org/10.5194/acp-22-1495-2022
Peng and Jimenez (2020): https://doi.org/10.1039/C9CS00766K
Shilling (1997): https://doi.org/10.2172/658267
Watne PhD thesis (2018): https://gupea.ub.gu.se/bitstream/handle/2077/54577/gupea_2077_54577_3.pdf?sequence=3
Zhao et al. (2008): https://doi.org/10.1016/j.atmosenv.2007.10.024
Ziemann and Atkinson (2012): https://doi.org/10.1039/C2CS35122FCitation: https://doi.org/10.5194/acp-2022-838-RC1 -
AC1: 'Reply on RC1', Zhancong Liang, 13 Feb 2023
The comment was uploaded in the form of a supplement: https://acp.copernicus.org/preprints/acp-2022-838/acp-2022-838-AC1-supplement.pdf
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AC1: 'Reply on RC1', Zhancong Liang, 13 Feb 2023
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RC2: 'Review of “Secondary Aerosol Formation in Incense Burning Particles by Ozonolysis and Photochemical Oxidation”', Anonymous Referee #2, 03 Feb 2023
This article describes a series of experiments used to explore the aging of incense particles in the presence of different oxidants by applying a flow reactor and a single particle mass spectrometer. The major conclusions are that nitrate formation on/in incense burning particles is enhanced in the presence of OH radicals relative to dark ozone oxidation and that oxalate and malonate formation is also enhanced in the presence of OH. While the experiments are interesting the main text and conclusions need more clarity around the actual implications of these findings for (presumably both indoor and outdoor) air quality and exposure.
Major comments
Section 3.2 is hard to follow and a clearer explanation and validation of the use of RPA and APA to draw conclusions is needed. A relatively low laser fluence was used in this work and partial ablation/matrix effects can be problematic for particles with secondary coatings (see Zelenyuk group research), which could lead to misclassification of particles based on ion intensities. The appearance of the nitrate-rich particle types after aging is quite conclusive though. Relative ionization/detection efficiencies for the different particle types are not discussed however, which would have a large impact on the relative particle type abundances shown in Figure 1. Some pure secondary organic particles (which may be externally mixed with primary particles in the reactor) for example are just not ionized effectively at all by SPMS. Some discussion of the drawbacks of SPMS are needed in the text.
Where is the NOx added? Or is it just the NOx from the combustion process. How were the NOx concentrations monitored or validated to be similar between experiments?
Figure S1 is missing the scrubber mentioned in the text.
Why are most of the figures in the supplementary information? There are only 3 main text figures and a lot of reference to the supplementary figures.
The manuscript is hard to follow in places, including the conclusions. A clear central message needs to be stated in the conclusions, with implications for air quality or public health.
No correlation (mentioned in the caption) is shown in Figure S4. Same for S6
Why was no support analysis done (especially ion chromatography for the oxalate/malonate yields) to rule out potential matrix-effect artifacts. Quantification (even semi-quantification) exclusively using SPMS is associated with high uncertainty.
Specific comments
Abstract- remove (photo-) because dark oxidation is also investigated
Page 2 line 58, missing ‘tracers’
“We studied the aging of the particles under 'UV', 'O3 and dark', and 'O3 and UV' in the PAM. Since UV at 254 nm is expected 81 to photolyze O3 to form OH radicals in the presence of water vapor, we named these aged particles UV-aged, O3-aged, and 82 OH-aged, respectively.”
Why not: ‘UV-aged’, ‘O3-dark-aged’ ‘O3-UV-aged’ for clarity
Where are the nitrate peaks in Figure 1b?
“The instrument 98 was routinely calibrated with polystyrene latex spheres of 0.2-2.5 μm diameter (Nanosphere Size Standards, Duke Scientific 99 Corp., Palo Alto)”
It should be specified that this only calibrates the sizing accuracy, not chemical species.
“and more than 98% of the particles were analyzed” should be “were classified”
“"K-" particles contain a dominant +39 peak and a small +41 peak attributed to isotopic 116 potassium (Bi et al., 2011). On the other hand, the "OC-" particles are rich in typical organic fragments such as +27[C2H3] (Cheng et al., 2017). According to the negative spectra, "-ON" particles have dominant ON signals. "-ONEC" particles have elemental carbon (EC) peaks of -12n[Cn - ], with intensities comparable to typical ON peaks (Zhou et al., 2020). "-Cl" particles have prominent Cl- (m/z=-35, -37(isotopic)) and KCl2 - (m/z=-109, -111(isotopic)) peaks (Bi et al., 2011).”
These are not the correct references for the original identification of these peaks by single particle mass spectrometry. See Prather group research.
“except for the rise of -62[NO3 - ] and -46[NO2 -], which indicates the formation of nitrate and probably nitrite”
Note that -46 is observed from nitrate and can’t be used to confirm nitrite
“However, the RPA shows an opposite trend, which can be interpreted as lower nitrate concentration in larger particles. Larger particles have larger surfaces but smaller surface-to-volume ratios, which lead to a larger absolute amount of nitrate formed but a lower relative concentration of particulate nitrate (Figure 2c, e). Under O3+UV, it is also possible that comparable HNO3 was generated under excess [OH] and contributed to the similar total nitrate RPA since the [NOx] reductions under different OH exposure are similarly high (Figure S10). The insensitivity of nitrate formation to O3 and OH exposure can be potentially explained by the diffusion limitation of interfacial uptake due to the poor hygroscopicity of fresh incense burning particles (Li and Hopke, 1993; Zaveri et al., 2018; Slade and Knopf, 2014; 220 Liang et al., 2022a)”
Caution should be taken interpreting the RPAs due to the potential for partial ablation and matrix effects.
“Figure 3a shows the NF ratio (aged particles to fresh particles) of oxalate and malonate. We used the NF ratio rather than the APA or RPA, to avoid large uncertainties in organic abundance due to the much weaker peaks of organics in the spectra.”
For the number fraction is there a query using a minimum APA or RPA for oxalate or malonate to be classified as a count? Furthermore, the point made here does raise the issue with using APAs/RPAs at all considering the potential for matrix effects.
Citation: https://doi.org/10.5194/acp-2022-838-RC2 -
AC2: 'Reply on RC2', Zhancong Liang, 13 Feb 2023
The comment was uploaded in the form of a supplement: https://acp.copernicus.org/preprints/acp-2022-838/acp-2022-838-AC2-supplement.pdf
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AC2: 'Reply on RC2', Zhancong Liang, 13 Feb 2023
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AC3: 'Comment on acp-2022-838—Tracked Manuscript', Zhancong Liang, 13 Feb 2023
The comment was uploaded in the form of a supplement: https://acp.copernicus.org/preprints/acp-2022-838/acp-2022-838-AC3-supplement.pdf
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AC4: 'Comment on acp-2022-838—SI', Zhancong Liang, 13 Feb 2023
The comment was uploaded in the form of a supplement: https://acp.copernicus.org/preprints/acp-2022-838/acp-2022-838-AC4-supplement.pdf
Interactive discussion
Status: closed
-
RC1: 'Anonymous review of “Secondary Aerosol Formation in Incense Burning Particles by Ozonolysis and Photochemical Oxidation” for Atmos. Chem. Phys.', Anonymous Referee #1, 09 Jan 2023
General Comments
Liang et al. (manuscript) describes the experimental formation of SOA and nitrate through chemical aging induced in an oxidation flow reactor (OFR). The authors injected combustion air from incense burning into the OFR at high RH, which were rapidly aged by controlling UV light and O3 to mimic UV-aged, O3-aged, and OH-aged scenarios. The authors used a single-particle AMS (SPAMS) to obtain the chemical composition of the particles and the Gothenburg PAM OFR (Go:PAM) as the reaction vessel.
The authors use the adaptive resonance theory method (ART-2a) algorithm to perform cluster/categorization analysis with the mass spectra (Zhao et al., 2008). The authors conclude that the OH-aged case generates more secondary nitrate than the O3-aged case based on the higher relative peak area (RPA). The enhanced secondary nitrate formation is attributed to higher uptake of nitrogen-containing species.
The manuscript overall lacks quantitative information, and I am confused about the OFR configuration. The authors provide some [NOx] information in Figure S10 and in the text, but a NOx instrument is not shown in the OFR set up in Figure S1. Moreover, the flow rates entering and exiting the OFR in Figure S1 already match, so adding a NOx monitor would cause a flow imbalance.
Moreover, the methodology and instrument details are lacking for replication, and additional explanations are needed to connect the chemistry in these OFR conditions to those of the atmosphere. For instance, the manuscript is missing the Go:PAM temperature and experiment residence times. The generated particle number concentrations from the WCPC, the particle mass collected on the filters for IC analysis, and the mass of incense used are not available. I do not have a clear picture of how much aerosol entered and exited the OFR.
The experiments and discussions fall within the scope of Atmos. Chem. Phys., and the content is topical to the atmospheric chemistry community. However, the manuscript is currently underprepared for publication, and there are technical issues that need resolution. Given the importance of understanding how chemical aging impacts aerosol evolution, I request the authors perform major revisions and resubmit the manuscript.
Specific Comments
1. The SPAMS calibration is not outlined, and details on the ART-2a solution is inadequate.
Details on the SPAMS operation would help assess the data quality. The Aerodyne soot particle AMS requires laser alignments for consistent measurements (Avery et al., 2020); does the SPAMS in this manuscript need a similar calibration? Particle transmission through the aerodynamic lens is size-dependent (Huang et al., 2013). How would size-dependent particle detection influence the data interpretation?The absolute peak area (APA), relative peak area RPA, and number fraction (NF) are frequently invoked in the data interpretation. The authors use APA and RPA as analogues to concentration (or fraction of total aerosol). However, I suspect that depends on how efficiently different species are ionized by the pulsed Nd:YAG laser, and I would like to know if adjustments have been made to the RPA based on the ionization efficiency. What is the ionization efficiency (IE) of species mentioned in the manuscript, and is IE consistent across species?
As for the ART-2a solution, Zhao et al. (2008) and Huang et al. (2013) note that there is no general rule for the vigilance factor, and that a comparative approach (like re-grouping or comparing with other clustering algorithms) may be needed. I also note there is no PAH category, despite particulate PAH found in previous incense combustion studies (Ji et al., 2010) and a PAH contribution being found in a similar mass spectrometer with ART-2a (Passig et al., 2022). Can the authors provide more detail and justification for their ART-2a solution?
2. OFR characterization and operation details are missing.
Offline OHexp calibrations may be inaccurate when OH reactive species suppressed OH. Basically, OH suppression is when the external OH reactivity (extOHR) entering the OFR is high enough to titrate the OH, which results in OH-aging being suppressed. In such scenarios, offline OHexp calibrations become unreliable, possibly by orders of magnitude (see Section 3.1.4 of Peng and Jimenez, 2020). Peng and Jimenez (2020) also notes that OFR254 is susceptible to OH suppression at low O3 injections.Operational information of the OFR would be valuable for replication and should be mentioned in the supplementary. Watne (2018) describes the Go:PAM as being made of quartz; have there been efforts to constrain electrostatic particle wall loss (Cao et al, 2020)? How would gas wall loss (Palm et al., 2016) affect the results reported, or is gas wall loss negligible? What cleaning procedure was taken to minimize carryover effects between experiments?
3. Kinetic modeling may be needed for interpretation.
The authors’ argument on secondary nitrate formation, either heterogeneously or in the gas phase is limited by the lack of quantification HNO3, HONO, NOx, NOy etc. The difference in condensed nitrate between the O3 and OH-aged cases may be due to differences in HNO3/HONO/NOx uptake as the authors allege. A kinetic calculation showing that the formation of these species under the difference OFR conditions are comparable would be more demonstrative.Moreover, gas-phase organic nitrate formation, either through VOC+NO3 or RO2+NO (Ziemann and Atkinson, 2012) and condensation should be considered. Kinetic modeling may be needed to connect the experimental aging conditions in the Go:PAM to those of the atmosphere (Peng and Jimenez, 2020).
Line 30: I recall incense burning is found in other cultures and am unsure if the practice is “especially” common in Asian and African religious rituals. I suggest either providing a reference for that point or removing “especially” in this sentence.
Line 35: The incense burning references cited here mention that there is variation in the particle emission factor (EF) across incense varieties. How does the particle EF in these experiments compare with those previous works? Were the combustion conditions comparable to those previous works?
Line 62: There is no information on the incense sticks used, like the manufacturer or composition, and Liang et al. (2022) used several as shown in their Figure S21. What type of incense was used here? How much incense was burned? This information could be valuable for replication studies.
Line 64: The methods reference (Liang et al., 2022) states there were four UVA lamps, while here the authors say they used “two UVC light tubes.” Please confirm that the Go-PAM set up had changed for this manuscript and specify that in the text. Moreover, what lamps were used? Rowe et al. (2020) found that 185 and 254 nm photon fluxes would vary across manufacturers, which may be re
Line 65: I am confused on how many experiments this manuscript is describing. I see in Figure 2 that there were 7 involving aging and 1 fresh; were some of these the “control” experiments? From this sentence I expect at least 2 types of controls, with either a charcoal absorber or HEPA filter. Were the control cases then also aged?
Line 66: How did the authors obtain these removal efficiencies?
Line 67: Compressed air or zero air? If the air is coming from a compressor, were efforts made to scrub the air of contaminants?
Line 74: The methods reference (Liang et al., 2022) does not mention using a diffusion dryer. At ~0.1 LPM, what was the residence time in the dryer and is there an estimate of particle loss in the dryer? Was the dryer effective in removing H2O?
Line 76: What were the estimated number of particles collected?
Line 83: Please provide additional details on the OHexp calibration with SO2, in particular the concentrations of SO2 used and timescales to reach equilibrium. An estimate of extOHR during the experiments should be compared with that of the SO2 calibrations.
Line 101: See specific comment 1.
Line 113: Explaining the abbreviations would improve readability. For instance, OC and ONEC do not appear prior in the text?
Line 147-149: How does the charcoal absorber remove NOx without removing VOC? How would the removal of VOC affect the interpretation here?
Line 156: How would the loss of SVOC/LVOC in the HEPA filter (Shilling, 1997) affect the conclusion of the control experiment?
Line 182: How did the authors arrive at the “~90 % reduction of [NOx]”? Was this a separate test? If so, please add a quick summary of how that test was performed.
Line 183: Was a NOx monitor available? If so, please provide the monitor’s location in Figure S1 and specify in the text. Also, please explain how the flow rates entering and exiting the Go:PAM would be reconciled.
Line 191-193: Do OH and O3 oxidation form similar functional groups? Are those functionalities evenly represented in these general markers? The RPA increase of SOA markers in OH over O3-aging may be skewed if these markers overrepresent one oxidation case over the other.
Line 214: Do larger and smaller particles have similar surface properties, at least with regards to nitrate uptake?
Line 222: I suspect SOA formation is not “potential,” but rather inevitable under the aforementioned OFR conditions, so I suggest removing “potential” from the section heading. Also, are oxalate and malonate universal and proportional indicators of SOA? That is, do different SOA precursors form these indicators evenly under different oxidants (O3/OH)? I am concerned that there are specific chemical conditions where these species are enhanced without a proportional enhancement of SOA, which may skew the NF.
Line 229: Is NF of oxalate and malonate proportional with SOA concentrations? As it stands, “30 and 9 folds” increases of these tracers sounds like SOA increased by that much.
Technical Comments
Line 47: Awkward grammar in “For instance … nitrate.”
Line 325: Please check the citation styles; they are inconsistent.
Lines 409/412: Same reference cited twice?
Figure 2: The data appears almost randomly scattered in the lower panels, which may be due to points heavily overlapping with each other. The authors may want to replace the box and whiskers/scatterplot with a violin plot for easier visualization.
Figure S1: Please display where the charcoal absorber, HEPA filter, and NOx instrument would have been placed.
References
Avery et al. (2020): https://doi.org/10.1080/02786826.2020.1844132
Cao et al. (2020): https://doi.org/10.1016/j.atmosenv.2019.117086
Huang et al. (2013): https://doi.org/10.1016/j.atmosenv.2012.09.044
Ji et al. (2010): https://doi.org/10.1111/j.1600-0668.2009.00634.x
Liang et al. (2022): https://doi.org/10.1021/acs.estlett.2c00492
Palm et al. (2016): https://doi.org/10.5194/acp-16-2943-2016
Passig et al. (2022): https://doi.org/10.5194/acp-22-1495-2022
Peng and Jimenez (2020): https://doi.org/10.1039/C9CS00766K
Shilling (1997): https://doi.org/10.2172/658267
Watne PhD thesis (2018): https://gupea.ub.gu.se/bitstream/handle/2077/54577/gupea_2077_54577_3.pdf?sequence=3
Zhao et al. (2008): https://doi.org/10.1016/j.atmosenv.2007.10.024
Ziemann and Atkinson (2012): https://doi.org/10.1039/C2CS35122FCitation: https://doi.org/10.5194/acp-2022-838-RC1 -
AC1: 'Reply on RC1', Zhancong Liang, 13 Feb 2023
The comment was uploaded in the form of a supplement: https://acp.copernicus.org/preprints/acp-2022-838/acp-2022-838-AC1-supplement.pdf
-
AC1: 'Reply on RC1', Zhancong Liang, 13 Feb 2023
-
RC2: 'Review of “Secondary Aerosol Formation in Incense Burning Particles by Ozonolysis and Photochemical Oxidation”', Anonymous Referee #2, 03 Feb 2023
This article describes a series of experiments used to explore the aging of incense particles in the presence of different oxidants by applying a flow reactor and a single particle mass spectrometer. The major conclusions are that nitrate formation on/in incense burning particles is enhanced in the presence of OH radicals relative to dark ozone oxidation and that oxalate and malonate formation is also enhanced in the presence of OH. While the experiments are interesting the main text and conclusions need more clarity around the actual implications of these findings for (presumably both indoor and outdoor) air quality and exposure.
Major comments
Section 3.2 is hard to follow and a clearer explanation and validation of the use of RPA and APA to draw conclusions is needed. A relatively low laser fluence was used in this work and partial ablation/matrix effects can be problematic for particles with secondary coatings (see Zelenyuk group research), which could lead to misclassification of particles based on ion intensities. The appearance of the nitrate-rich particle types after aging is quite conclusive though. Relative ionization/detection efficiencies for the different particle types are not discussed however, which would have a large impact on the relative particle type abundances shown in Figure 1. Some pure secondary organic particles (which may be externally mixed with primary particles in the reactor) for example are just not ionized effectively at all by SPMS. Some discussion of the drawbacks of SPMS are needed in the text.
Where is the NOx added? Or is it just the NOx from the combustion process. How were the NOx concentrations monitored or validated to be similar between experiments?
Figure S1 is missing the scrubber mentioned in the text.
Why are most of the figures in the supplementary information? There are only 3 main text figures and a lot of reference to the supplementary figures.
The manuscript is hard to follow in places, including the conclusions. A clear central message needs to be stated in the conclusions, with implications for air quality or public health.
No correlation (mentioned in the caption) is shown in Figure S4. Same for S6
Why was no support analysis done (especially ion chromatography for the oxalate/malonate yields) to rule out potential matrix-effect artifacts. Quantification (even semi-quantification) exclusively using SPMS is associated with high uncertainty.
Specific comments
Abstract- remove (photo-) because dark oxidation is also investigated
Page 2 line 58, missing ‘tracers’
“We studied the aging of the particles under 'UV', 'O3 and dark', and 'O3 and UV' in the PAM. Since UV at 254 nm is expected 81 to photolyze O3 to form OH radicals in the presence of water vapor, we named these aged particles UV-aged, O3-aged, and 82 OH-aged, respectively.”
Why not: ‘UV-aged’, ‘O3-dark-aged’ ‘O3-UV-aged’ for clarity
Where are the nitrate peaks in Figure 1b?
“The instrument 98 was routinely calibrated with polystyrene latex spheres of 0.2-2.5 μm diameter (Nanosphere Size Standards, Duke Scientific 99 Corp., Palo Alto)”
It should be specified that this only calibrates the sizing accuracy, not chemical species.
“and more than 98% of the particles were analyzed” should be “were classified”
“"K-" particles contain a dominant +39 peak and a small +41 peak attributed to isotopic 116 potassium (Bi et al., 2011). On the other hand, the "OC-" particles are rich in typical organic fragments such as +27[C2H3] (Cheng et al., 2017). According to the negative spectra, "-ON" particles have dominant ON signals. "-ONEC" particles have elemental carbon (EC) peaks of -12n[Cn - ], with intensities comparable to typical ON peaks (Zhou et al., 2020). "-Cl" particles have prominent Cl- (m/z=-35, -37(isotopic)) and KCl2 - (m/z=-109, -111(isotopic)) peaks (Bi et al., 2011).”
These are not the correct references for the original identification of these peaks by single particle mass spectrometry. See Prather group research.
“except for the rise of -62[NO3 - ] and -46[NO2 -], which indicates the formation of nitrate and probably nitrite”
Note that -46 is observed from nitrate and can’t be used to confirm nitrite
“However, the RPA shows an opposite trend, which can be interpreted as lower nitrate concentration in larger particles. Larger particles have larger surfaces but smaller surface-to-volume ratios, which lead to a larger absolute amount of nitrate formed but a lower relative concentration of particulate nitrate (Figure 2c, e). Under O3+UV, it is also possible that comparable HNO3 was generated under excess [OH] and contributed to the similar total nitrate RPA since the [NOx] reductions under different OH exposure are similarly high (Figure S10). The insensitivity of nitrate formation to O3 and OH exposure can be potentially explained by the diffusion limitation of interfacial uptake due to the poor hygroscopicity of fresh incense burning particles (Li and Hopke, 1993; Zaveri et al., 2018; Slade and Knopf, 2014; 220 Liang et al., 2022a)”
Caution should be taken interpreting the RPAs due to the potential for partial ablation and matrix effects.
“Figure 3a shows the NF ratio (aged particles to fresh particles) of oxalate and malonate. We used the NF ratio rather than the APA or RPA, to avoid large uncertainties in organic abundance due to the much weaker peaks of organics in the spectra.”
For the number fraction is there a query using a minimum APA or RPA for oxalate or malonate to be classified as a count? Furthermore, the point made here does raise the issue with using APAs/RPAs at all considering the potential for matrix effects.
Citation: https://doi.org/10.5194/acp-2022-838-RC2 -
AC2: 'Reply on RC2', Zhancong Liang, 13 Feb 2023
The comment was uploaded in the form of a supplement: https://acp.copernicus.org/preprints/acp-2022-838/acp-2022-838-AC2-supplement.pdf
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AC2: 'Reply on RC2', Zhancong Liang, 13 Feb 2023
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AC3: 'Comment on acp-2022-838—Tracked Manuscript', Zhancong Liang, 13 Feb 2023
The comment was uploaded in the form of a supplement: https://acp.copernicus.org/preprints/acp-2022-838/acp-2022-838-AC3-supplement.pdf
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AC4: 'Comment on acp-2022-838—SI', Zhancong Liang, 13 Feb 2023
The comment was uploaded in the form of a supplement: https://acp.copernicus.org/preprints/acp-2022-838/acp-2022-838-AC4-supplement.pdf
Zhancong Liang et al.
Zhancong Liang et al.
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