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

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

doi:10.5194/acp-20-12363-2020

Abstract

Abstract. We report on airborne measurements of tropospheric mixing ratios and vertical profiles of formaldehyde (CH2O), glyoxal (C2H2O2), methylglyoxal and higher carbonyls (C3H4O2*) (see below), and carbon monoxide (CO) 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 CO and remotely measured CH2O, C2H2O2, and C3H4O2*, 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 C2H2O2 and C3H4O2* with respect to CH2O are inferred and compared to recent studies. The mean glyoxal-to-formaldehyde ratio RGF=0.07 (range 0.02–0.11) is in good agreement with recent reports which suggest RGF to be significantly lower than previously assumed in global chemical transport models (CTMs). The mean methylglyoxal-to-formaldehyde ratio RMF=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 2.0±0.5 to account for the additional dicarbonyls included in the C3H4O2* measurements. Using recently reported emission factors of CH2O for tropical forests, our observations suggest emission factors of EFG=0.25 (range 0.11 to 0.52) g kg−1 for C2H2O2 and EFM = 4.7 (range 0.5 to 8.64) g kg−1 for C3H4O2*. While EFG agrees well with recent reports, EFM is (like RMF) 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.

Highlights

Emissions from biomass burning are a large source of reactive gases and particulate matter to the atmosphere on local, regional, and up to the global scale (Crutzen and Andreae, 1990; Andreae and Merlet, 2001; Andreae et al, 2001; Andreae, 2019)
Notable are the peaks in carbon monoxide (CO) while flying through the Manaus city plume or biomass burning plumes
Elevated mixing ratios of CH2O, C2H2O2, and C3H4O∗2 can be related to biomass burning as well as to air masses of presumably aged background air as evidenced by the only moderately elevated CO

Summary

Introduction

Emissions from biomass burning are a large source of reactive gases and particulate matter to the atmosphere on local, regional, and up to the global scale (Crutzen and Andreae, 1990; Andreae and Merlet, 2001; Andreae et al, 2001; Andreae, 2019). Pyrogenic emissions form a complex mixture of species that can change over the duration of the fire and undergo further chemical reactions as emissions are transported downwind. F. Kluge et al.: Biomass burning have adverse effects on the atmospheric photochemistry, secondary aerosol formation and composition, and cloud formation and radiation, as well as human health. Accurate measurements of pyrogenic emissions, the evolution of fire plume composition, and the formation and ageing of aerosols are needed, but respective data are lacking for many species Accurate measurements of pyrogenic emissions, the evolution of fire plume composition, and the formation and ageing of aerosols are needed, but respective data are lacking for many species (e.g. Andreae and Merlet, 2001; Akagi et al, 2011; Stockwell et al, 2015; Andreae, 2019)

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Discussion

Conclusion