| dc.description.abstract | We report simultaneous measurements of volatile organic compound (VOC) mixing ratios
including C-6 to C-8 aromatics, isoprene, monoterpenes, acetone and organic aerosol mass
loadings at a rural location in southwestern Ontario, Canada by Proton-Transfer-Reaction
Mass Spectrometry (PTR-MS) and Aerosol Mass Spectrometry (AMS), respectively. During the
three-week-long Border Air Quality and Meteorology Study in June-July 2007, air was
sampled from a range of sources, including aged air from the polluted US Midwest, direct
outflow from Detroit 50 km away, and clean air with higher biogenic input. After
normalization to the diurnal profile of CO, a long-lived tracer, diurnal analyses show
clear photochemical loss of reactive aromatics and production of oxygenated VOCs and
secondary organic aerosol (SOA) during the daytime. Biogenic VOC mixing ratios increase
during the daytime in accord with their light-and temperature-dependent sources.
Long-lived species, such as hydrocarbon-like organic aerosol and benzene show little to
no photochemical reactivity on this timescale. From the normalized diurnal profiles of
VOCs, an estimate of OH concentrations during the daytime, measured O-3 concentrations,
and laboratory SOA yields, we calculate integrated local organic aerosol production
amounts associated with each measured SOA precursor. Under the assumption that biogenic
precursors are uniformly distributed across the southwestern Ontario location, we
conclude that such precursors contribute significantly to the total amount of SOA
formation, even during the period of Detroit outflow. The importance of aromatic
precursors is more difficult to assess given that their sources are likely to be
localized and thus of variable impact at the sampling location. | en_US |
