Environ Sci Technol

Nitrogen dioxide (NO|) not only is linked to adverse effects on the respiratory system but also contributes to the formation of ground-level ozone (O|) and fine particulate matter (PM|). Our curbside monitoring data analysis in Detroit, MI, and Atlanta, GA, strongly suggests that a large fraction of NO| is produced during the "tailpipe-to-road" stage. To substantiate this finding, we designed and carried out a field campaign to measure the same exhaust plumes at the tailpipe-level by a portable emissions measurement system (PEMS) and at the on-road level by an electric vehicle-based mobile platform. Furthermore, we employed a turbulent reacting flow model, CTAG, to simulate the on-road chemistry behind a single vehicle. We found that a three-reaction (NO-NO|-O|) system can largely capture the rapid NO to NO| conversion (with time scale 48 seconds) observed in the field studies. To distinguish the contributions from different mechanisms to near-road NO|, we clearly defined a set of NO|/NO | ratios at different plume evolution stages, namely tailpipe, on-road, curbside, near-road, and ambient background. Our findings from curbside monitoring, on-road experiments, and simulations imply the on-road oxidation of NO by ambient O| is a significant, but so far ignored, contributor to curbside and near-road NO|.EPA999999/ImEPA/Intramural EPA/United StatesP30 ES017885/ES/NIEHS NIH HHS/United StatesT42 OH008455/OH/NIOSH CDC HHS/United States2019-04-15T00:00:00Z29565574PMC64632988772vault:3563