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| 14 May 2025
Technical note: Apportionment of Southeast Asian Biomass Burning and Urban Influence via In Situ Trace Gas Enhancement Ratios
Abstract. Biomass burning and urban emissions are major contributors to poor air quality throughout Southeast Asia. Understanding these emissions is critical for predicting and mitigating their health impacts. The Cloud, Aerosol and Monsoon Processes Philippines Experiment (CAMP2Ex) field project in 2019 focused on regional sources in Southeast Asia and their effects on aerosol/cloud interactions using a combination of airborne, shipboard, and ground-based platforms. These measurements sampled a variety of pollution sources over the Sulu, Philippine, and South China seas during both the southwest monsoon and monsoon transition periods. CAMP2Ex provided a unique opportunity to examine how local and transported emissions affected airmass chemical composition and air quality. Correlations in airborne in situ gas enhancement ratios of CH4 to CO were used to separate airmasses with predominantly biomass burning, urban, or mixed influence, and isolating contributions from differing urban sources. HYSPLIT backtrajectory analysis was used to identify airmass sources, and resulting source regimes were examined for differences in ozone, reactive nitrogen, and aerosol chemical composition. ΔO3/ΔCO enhancement ratios were observed to be constant between urban source regimes, yet ΔNOy/ΔCO enhancement ratios differed across these regimes. For biomass burning sources, enhancement ratios in ΔO3/ΔCO were lower than those reported by previous studies in this region. Organic aerosol mass fractions were 2–3 times higher in biomass burning influenced regimes compared to urban regimes. This technique represents a simple yet novel approach for separating emission influences in a complex environment that enable isolation of emission sources requiring relatively simple measurements.
Competing interests: Armin Sorooshian is an editor for Atmospheric Chemistry and Physics.
Publisher's note: Copernicus Publications remains neutral with regard to jurisdictional claims made in the text, published maps, institutional affiliations, or any other geographical representation in this preprint. The responsibility to include appropriate place names lies with the authors.- Preprint
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Status: open (until 26 Jun 2025)
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RC1: 'Comment on egusphere-2025-1454', Anonymous Referee #1, 13 Jun 2025
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Review of "Technical note: Apportionment of Southeast Asian Biomass Burning and Urban Influence via In Situ Trace Gas Enhancement Ratios" by DiGangi and coauthors
This is a straightforward technical note presenting the usefulness of enhancement ratios of CH4 to CO to identify/constrain various origin source signatures in regions influenced by various air masses transported to a measurement location. This technique is reasonably sound and appears to be useful for apportioning data from different source regimes in the absence of measurements of more specific chemical tracers (i.e., VOCs or other non-organic gases like HCN that are emitted nearly exclusively from specific anthropogenic or biomass burning emissions sources.) This should be made clear in the paper.
Once this and the following comments and technical corrections are addressed, this technical note should be published in ACP.
Lines 129-130 and Figure S1: The brief description of the use of a ±5 ppb CO and CH4 hysteresis could use a little more explanation. The dashed lines for CH4, 1.85 + 0.04 = 1.89 ppm, and ± 5 ppb (± 0.005 ppb) would be 1.885 – 1.895, and for CO, 65 ppb + 55 ppb = 120 ppb, and then ± 5 ppb would be from 115-125 ppb? The dashed lines in Fig. S1 are each 5 ppb above those (1.89 – 1.90 ppm for CH4 and 120 – 130 for CO), which seem too high for the explanation given in the text.
Technical corrections:
Lines 14, 73, 78, etc.: “Seas” should be capitalized.
Lines 21, 22, 23, 36, 38, etc.: “air mass” and “air masses” should both be two words.
Line 29: I believe it should be “enables” (novel approach is singular).
Line 53: it would be better to spell out “many days to weeks”.
Lines 118, 137, and Figs. 2 and S2 captions: “vs.” should have a period.
Line 130: Supplemental Fig. S1. (Technically, “Supplemental” isn’t needed, either – the S is sufficient.) (Similarly, Fig. S2 – line 157).
Figure 2 caption: I recommend making this a proper sentence: “… colored by regime excluding Clark-influenced data using (a) a global background method, (b) a rolling slope method, and (c) a final combined method.”
Table 1: in the first column there are two CH4s that need the 4s subscripted.
Lines 156-158: This sentence seems awkward. I recommend either add another comma, or change the comma to a semicolon and add a “was” before identified, maybe?
Line 160: remove “ Jr.” -- generally, suffixes aren’t included in in-text citations.
Line 161: Fig. S2c-d -- it is still a single figure being referenced.
Lines 182, 191, Fig. 3 caption, etc.: “back trajectory” and “back trajectories” should each be two words.
Line 191: “Figure 3 shows…”
Line 219: “Figure 4a shows…”
Line 223: remove “the” before “February-April”
Line 228: “Fig. 4b”
Line 215: The legend colors in Fig. 5 do not correspond to the colors in the pie charts in (a)-(f).
Lines 245 and 253: Maybe use “BB/urban” similar to the Fig. 5g category name instead of “biomass/urban”, to be clear that this isn’t a mixture of biogenic and urban emissions.
Line 250: “Fig. 5a”
Line 257: “Figure 6 shows…”
Line 260: delete one “urban”.
Line 270: remove “sloped” x2: “… with higher ΔCH4/ΔCO corresponding to local emissions and lower ΔCH4/ΔCO corresponding…” Similarly, consider using “relationship” instead of “slope” in the rest of this paragraph.
Lines 305-end: I believe the journal names should be abbreviated.
Line 347: there is a rogue “$” in the CAMP2Ex name.
Line 411: CO2 should have a subscripted 2.
Citation: https://doi.org/10.5194/egusphere-2025-1454-RC1
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