Profiling of formaldehyde, glyoxal, methylglyoxal, and CO over the Amazon: normalized excess mixing ratios and related emission factors in biomass burning plumes

Kluge, Flora; Hüneke, Tilman; Knecht, Matthias; Lichtenstern, Michael; Rotermund, Meike; Schlager, Hans; Schreiner, Benjamin; Pfeilsticker, Klaus

We report on airborne measurements of tropospheric mixing ratios and vertical profiles of formaldehyde (inline-formulaCH2O), glyoxal (inline-formulaC2H2O2), methylglyoxal and higher carbonyls (inline-formula M3inlinescrollmathml chem normal C normal 3 normal H normal 4 normal O normal 2 * 41pt14ptsvg-formulamathimgaf988864cbcdcafdc3df86b6a358936b acp-20-12363-2020-ie00001.svg41pt14ptacp-20-12363-2020-ie00001.png ) (see below), and carbon monoxide (inline-formulaCO) over the Amazon Basin during the ACRIDICON-CHUVA campaign from the German High Altitude and Long-range research aircraft (HALO) in autumn 2014. The joint observation of in situ inline-formulaCO and remotely measured inline-formulaCH2O, inline-formulaC2H2O2, and inline-formula M8inlinescrollmathml chem normal C normal 3 normal H normal 4 normal O normal 2 * 41pt14ptsvg-formulamathimgef1d34cc9d4b75383356dfc5a6d1cdf1 acp-20-12363-2020-ie00002.svg41pt14ptacp-20-12363-2020-ie00002.png , together with visible imagery and air mass back-trajectory modelling using NOAA HYSPLIT (National Oceanic Atmospheric Administration, HYbrid Single-Particle Lagrangian Integrated Trajectory), allows us to discriminate between the probing of background tropical air, in which the concentration of the measured species results from the oxidation of biogenically emitted volatile organic compounds (VOCs, mostly isoprene), and measurements of moderately to strongly polluted air masses affected by biomass burning emissions or the city plume of Manaus. For 12 near-surface measurements of fresh biomass burning plumes, normalized excess mixing ratios of inline-formulaC2H2O2 and inline-formula M10inlinescrollmathml chem normal C normal 3 normal H normal 4 normal O normal 2 * 41pt14ptsvg-formulamathimg2ed961b4f0644d9e3f0f6f3d6a5f4cd1 acp-20-12363-2020-ie00003.svg41pt14ptacp-20-12363-2020-ie00003.png with respect to inline-formulaCH2O are inferred and compared to recent studies. The mean glyoxal-to-formaldehyde ratio inline-formulaRGF=0.07 (range 0.02–0.11) is in good agreement with recent reports which suggest inline-formulaRGF to be significantly lower than previously assumed in global chemical transport models (CTMs). The mean methylglyoxal-to-formaldehyde ratio inline-formulaRMF=0.98 (range 0.09–1.50) varies significantly during the different observational settings but overall appears to be much larger (up to a factor of 5) than previous reports suggest even when applying a correction factor of inline-formula2.0±0.5 to account for the additional dicarbonyls included in the inline-formula M16inlinescrollmathml chem normal C normal 3 normal H normal 4 normal O normal 2 * 41pt14ptsvg-formulamathimg49b151acafa38023d601c2a77f7be38e acp-20-12363-2020-ie00004.svg41pt14ptacp-20-12363-2020-ie00004.png measurements. Using recently reported emission factors of inline-formulaCH2O for tropical forests, our observations suggest emission factors of inline-formulaEFG=0.25 (range 0.11 to 0.52) inline-formulag kg−1 for inline-formulaC2H2O2 and inline-formulaEFM = 4.7 (range 0.5 to 8.64) inline-formulag kg−1 for inline-formula M23inlinescrollmathml chem normal C normal 3 normal H normal 4 normal O normal 2 * 41pt14ptsvg-formulamathimg9b23584d462cefbaaa486b5b3c5dfaa8 acp-20-12363-2020-ie00005.svg41pt14ptacp-20-12363-2020-ie00005.png . While inline-formulaEFG agrees well with recent reports, inline-formulaEFM is (like inline-formulaRMF) slightly larger than reported in other studies, presumably due to the different plume ages or fuels studied. Our observations of these critical carbonyls and intermediate oxidation products may support future photochemical modelling of air pollution over tropical vegetation, as well as validate past and present space-borne observations of the respective species.

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Kluge, Flora / Hüneke, Tilman / Knecht, Matthias / et al: Profiling of formaldehyde, glyoxal, methylglyoxal, and CO over the Amazon: normalized excess mixing ratios and related emission factors in biomass burning plumes. 2020. Copernicus Publications.

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