Primary emissions of glyoxal and methylglyoxal from laboratory measurements of open biomass burning

Abstract. We report the emissions of glyoxal and methylglyoxal from the open burning of biomass during the NOAA-led 2016 FIREX intensive at the Fire Sciences Laboratory in Missoula, MT. Both compounds were measured using cavity enhanced spectroscopy, which is both more sensitive and more selective than methods previously used to determine emissions of these two compounds. A total of 75 burns were conducted, using 33 different fuels in 8 different categories, providing a far more comprehensive dataset for emissions than was previously available. Measurements of methylglyoxal using our instrument suffer from spectral interferences from several other species, but methylglyoxal emissions could be constrained within roughly a factor of 2. Methylglyoxal emissions were 2–3 times higher than glyoxal emissions on a molar basis, in contrast to previous studies that report methylglyoxal emissions lower than glyoxal emissions. Methylglyoxal emission ratios for all fuels averaged 3.6 ± 2.4 ppbv methylglyoxal/ppmv CO, while emission factors averaged 0.66 ± 0.50 g methylglyoxal/kg fuel burned. Primary emissions of glyoxal from biomass burning were much lower than previous laboratory measurements, but consistent with recent measurements from aircraft. Glyoxal emission ratios for all fuels averaged 1.4 ± 0.7 ppbv glyoxal/ppmv CO, while emission factors averaged 0.20 ± 0.12 g glyoxal/kg fuel burned, values that are at least a factor of 4 lower than assumed in previous estimates of the global glyoxal budget. While there was significant variability in the glyoxal emission ratios and factors between the different fuel groups, glyoxal and formaldehyde were highly correlated during the course of any given fire, and the ratio of glyoxal to formaldehyde, RGF, was consistent across many different fuel types, with an average value of 0.068 ± 0.018. While RGF values for fresh emissions were consistent across many fuel types, further work is required to determine how this value changes as the emissions age.