Isocyanic acid in a global chemistry transport model: Tropospheric distribution, budget, and identification of regions with potential health impacts

Abstract

[1] This study uses a global chemical transport model to estimate the distribution of isocyanic acid (HNCO). HNCO is toxic, and concentrations exceeding 1 ppbv have been suggested to have negative health effects. Based on fire studies, HNCO emissions were scaled to those of hydrogen cyanide (30%), resulting in yearly total emissions of 1.5 Tg for 2008, from both anthropogenic and biomass burning sources. Loss processes included heterogeneous uptake (pH dependent), dry deposition (like formic acid), and reaction with the OH radical (k = 1 Â 10 À15 molecule À1 cm 3 s À1 ). Annual mean surface HNCO concentrations were highest over parts of China (maximum of 470 pptv), but episodic fire emissions gave much higher levels, exceeding 4 ppbv in tropical Africa and the Amazon, and exceeding 10 ppbv in Southeast Asia and Siberia. This suggests that large biomass burning events could result in deleterious health effects for populations in these regions. For the tropospheric budget, using the model-calculated pH the HNCO lifetime was 37 days, with the split between dry deposition and heterogeneous loss being 95%:5%. Fixing the heterogeneous loss rate at pH = 7 meant that this process dominated, accounting for $70% of the total loss, giving a lifetime of 6 days, and resulting in upper tropospheric concentrations that were essentially zero. However, changing the pH does not notably impact the high concentrations found in biomass burning regions. More observational data is needed to evaluate the model, as well as a better representation of the likely underestimated biofuel emissions, which could mean more populations exposed to elevated HNCO concentrations.

Tropospheric sources and sinks of gas-phase acids in the Colorado Front Range

“…Dry deposition is a major sink of HNCO (Roberts et al, 2014;Young et al, 2012), although HNCO readily partitions into the aqueous phase (H = 10 5 mol L −1 atm −1 ), where it can hydrolyze to NH 3 . We estimate that aqueous partitioning of HNCO was negligible.…”

“…HNCO is of growing interest because exposure levels > 1 ppb v are linked to various human health issues, including atherosclerosis, cataracts, and rheumatoid arthritis (Jaisson et al, 2011;Roberts et al, 2011). Primary emission and secondary photochemical production sources of gas-phase HNCO have been identified and reported (Borduas et al, 2013;Roberts et al, 2014), but the magnitudes of these sources remain highly uncertain (Young et al, 2012). Combustion processes, including biomass burning, gasoline/diesel fuel combustion, and tobacco smoke are a primary source of HNCO (Roberts et al, , 2014Link et al, 2016).…”

“…HNCO readily partitions into the aqueous-phase given its high solubility at atmospherically relevant pH values, and can hydrolyze to NH 3 . Wet and dry deposition are other known HNCO sinks (Young et al, 2012;Roberts et al, 2014).…”

Modelling atmospheric oxidation of 2-aminoethanol (MEA) emitted from post-combustion capture using WRF–Chem

“…Ambient isocyanic acid mixing ratios of typically 100 pptv have been measured (Roberts et al, 2013), while mixing ratios above 1 ppbv were found in the plumes from biomass burning or in regions impacted by domestic wood burning and wild fires (Young et al, 2012;Roberts et al, 2013). Several countries regulate the occupational exposure from isocyanates but no explicit guidelines exist for the ambient health risk.…”

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

“…Historically, biomass burning was considered to be the dominant global source of both 5 HNCO (Veres et al, 2010;Roberts et al, 2011;Young et al, 2012) and HCN (Li et al, 2000;Li et al, 6 2003;Li et al, 2009;Shim et al, 2007). Global HCN (Li et al, 2003) and HNCO (Young et al, 2012) 7 models have hitherto considered vehicle sources of these compounds to be negligible.…”