This study investigates a significant biomass burning (BB) event occurred in Colorado of the United States in 2012 using the Community Multi-scale Air Quality (CMAQ) model. The simulation reasonably reproduced the significantly high upper tropospheric O concentrations (up to 145ppb) caused by BB emissions. We find the BB-induced O was primarily affected by chemical reactions and dispersion during its transport. In the early period of transport, high NO and VOCs emissions caused O production due to reactions with the peroxide and hydroxyl radicals, HO and OH. Here, NO played a key role in O formation in the BB plume. The results indicated that HO in the BB plume primarily came from formaldehyde (HCHO+hv=2HO+CO), a secondary alkoxy radical (ROR=HO). CO played an important role in the production of recycled HO (OH+CO=HO) because of its abundance in the BB plume. The chemically produced HO was largely converted to OH by the reactions with NO (HO+NO=OH+NO) from BB emissions. This is in contrast to the surface, where HO and OH are strongly affected by VOC and HONO, respectively. In the late stages of transport, the O concentration was primarily controlled by dispersion. It stayed longer in the upper troposphere compared to the surface due to sustained depletion of NO. Sensitivity analysis results support that O in the BB plume is significantly more sensitive to NO than VOCs.
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| http://dx.doi.org/10.1016/j.scitotenv.2017.09.177 | DOI Listing |
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