Large unexplained suite of chemically reactive compounds present in ambient air due to biomass fires

Abstract

Biomass fires impact global atmospheric chemistry. The reactive compounds emitted and formed due to biomass fires drive ozone and organic aerosol formation, affecting both air quality and climate. Direct hydroxyl (OH) Reactivity measurements quantify total gaseous reactive pollutant loadings and comparison with measured compounds yields the fraction of unmeasured compounds. Here, we quantified the magnitude and composition of total OH reactivity in the north-west Indo-Gangetic Plain. More than 120% increase occurred in total OH reactivity (28 s−1 to 64 s−1) and from no missing OH reactivity in the normal summertime air, the missing OH reactivity fraction increased to ~40 % in the post-harvest summertime period influenced by large scale biomass fires highlighting presence of unmeasured compounds. Increased missing OH reactivity between the two summertime periods was associated with increased concentrations of compounds with strong photochemical source such as acetaldehyde, acetone, hydroxyacetone, nitromethane, amides, isocyanic acid and primary emissions of acetonitrile and aromatic compounds. Currently even the most detailed state-of-the art atmospheric chemistry models exclude formamide, acetamide, nitromethane and isocyanic acid and their highly reactive precursor alkylamines (e.g. methylamine, ethylamine, dimethylamine, trimethylamine). For improved understanding of atmospheric chemistry-air quality-climate feedbacks in biomass-fire impacted atmospheric environments, future studies should include these compounds.

Elucidating real-world vehicle emission factors from mobile measurements over a large metropolitan region: a focus on isocyanic acid, hydrogen cyanide, and black carbon

“…The background (BKG) was subsequently defined as the rolling second percentile over a 90-point (180 s) window, with additional boxcar smoothing over the same window. Similar approaches for estimating background concentrations from mobile monitoring studies have been employed by others (Jiang et al, 2005;Jimenez et al, 2000;Hudda et al, 2013;Park et al, 2011;Bukowiecki et al, 2002;Larson et al, 2017).…”

“…As such, past measurements of these species have focussed on regions heavily influenced by biomass burning or, in the case of HCN, on the upper troposphere or total tropospheric column. Although the advent of chemical ionization mass spectrometers has allowed for real-time measurements of atmospherically relevant concentrations of these species (Roberts et al, 2011;Veres et al, 2008;Woodward-Massey et al, 2014;Le Breton et al, 2013;Knighton et al, 2009), there remain relatively few measurements of ambient HNCO (Roberts et al, 2011(Roberts et al, , 2014Wentzell et al, 2013;Zhao et al, 2014;Woodward-Massey et al, 2014;Sarkar et al, 2016;Chandra and Sinha, 2016;Kumar et al, 2018). Measurements of ground-level HCN in both rural and urban environments with minimal BB influence are more limited (Ambrose et al, 2010).…”

“…However, given the recent studies suggesting that HCN and HNCO emissions from vehicles could be significant, especially at a local scale, a better understanding of on-road emissions of these species is necessary. Moreover, ambient measurements are suggestive of a secondary source of HNCO (Roberts et al, 2011(Roberts et al, , 2014Wentzell et al, 2013;Zhao et al, 2014;Sarkar et al, 2016;Kumar et al, 2018) formed photochemically by the photooxidation of precursors such as alkyl amines and amides (Borduas et al, 2013(Borduas et al, , 2015Sarkar et al, 2016). Recent studies (Jathar et al, 2017;Link et al, 2016) show that diesel engine exhaust itself contains precursors leading to enhanced photochemical production of HNCO, even further underscoring the need to quantify vehicular emissions of HNCO in dense, urban environments.…”

Constraining Emissions of Volatile Organic Compounds Over the Indian Subcontinent Using Space‐Based Formaldehyde Measurements

“…VOC emission estimates from alternate fire inventories (Streets et al, ; Venkataraman et al, ; Wiedinmyer et al, ) are >2 times higher than GFEDv4, providing support for this contention. Contributing factors could include underestimated sources such as municipal waste burning (Sharma et al, ) or uncharacterized pyrogenic VOCs (Kumar et al, ).…”

“…Contributing factors could include underestimated sources such as municipal waste burning (Sharma et al, 2019) or uncharacterized pyrogenic VOCs (Kumar et al, 2018).…”