Photochemical processing of organic aerosol at nearby continental sites: contrast between urban plumes and regional aerosol
Date
2011
Authors
Slowik, J. G.
Brook, J.
Chang, R. Y-W
Evans, G. J.
Hayden, K.
Jeong, C-H
Li, S-M
Liggio, J.
Liu, P. S. K.
McGuire, M.
Journal Title
Journal ISSN
Volume Title
Publisher
Abstract
As part of the BAQS-Met 2007 field campaign, Aerodyne time-of-flight aerosol mass
spectrometers (ToF-AMS) were deployed at two sites in southwestern Ontario from 17 June
to 11 July 2007. One instrument was located at Harrow, ON, a rural,
agriculture-dominated area approximately 40 km southeast of the Detroit/Windsor/Windsor
urban area and 5 km north of Lake Erie. The second instrument was located at Bear Creek,
ON, a rural site approximately 70 km northeast of the Harrow site and 50 km east of
Detroit/Windsor. Positive matrix factorization analysis of the combined organic mass
spectral dataset yields factors related to secondary organic aerosol (SOA), direct
emissions, and a factor tentatively attributed to the reactive uptake of isoprene and/or
condensation of its early generation reaction products. This is the first application of
PMF to simultaneous AMS measurements at different sites, an approach which allows for
self-consistent, direct comparison of the datasets. Case studies are utilized to
investigate processing of SOA from (1) fresh emissions from Detroit/Windsor and (2)
regional aerosol during periods of inter-site flow. A strong correlation is observed
between SOA/excess CO and photochemical age as represented by the NOx/NOy ratio for
Detroit/Windsor outflow. Although this correlation is not evident for more aged air,
measurements at the two sites during inter-site transport nevertheless show evidence of
continued atmospheric processing by SOA production. However, the rate of SOA production
decreases with airmass age from an initial value of similar to 10.1 mu g m(-3)
ppmv(CO)(-1) h(-1) for the first similar to 10 h of plume processing to near-zero in an
aged airmass (i.e. after several days). The initial SOA production rate is comparable to
the observed rate in Mexico City over similar timescales.
Description
Keywords
Citation
Slowik, J. G., J. Brook, R. Y-W Chang, G. J. Evans, et al. 2011. "Photochemical processing of organic aerosol at nearby continental sites: contrast
between urban plumes and regional aerosol." Atmospheric Chemistry and Physics 11(6): 2991-3006.