Photochemical processing of organic aerosol at nearby continental sites: contrast between urban plumes and regional aerosol

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 NO<sub>x</sub>/NO<sub>y</sub> 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 ~10.1 μg m<sup>−3</sup> ppmv<sub>CO</sub><sup>−1</sup> h<sup>−1</sup> for the first ~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

Aircraft study of the impact of lake-breeze circulations on trace gases and particles during BAQS-Met 2007

“…A detailed analysis of the meteorology and lake breezes observed throughout the study has been described elsewhere (e.g. OME, 2008; Sills et al, 2011;Slowik et al, 2011). The synoptic wind flow was determined from the high resolution back trajectories computed for air parcels arriving into the study region at 500 m a.g.l.…”

Mass spectrometric approaches for chemical characterisation of atmospheric aerosols: critical review of the most recent advances

“…[82] In recent years, positive matrix factorisation (PMF) analysis has become a common tool for AMS data analysis and provided valuable information about sources of OAs and their atmospheric evolution at many locations affected by anthropogenic emissions. [83] Specifically, a hydrocarbon-like OA (HOA) factor was attributed to primary aerosols emissions associated with urban traffic, [84][85][86][87][88][89][90] residential heating using solid fuel and wood, [86][87][88] fossil fuel combustion and biomass burning [84] and food cooking and charbroiling. [87] The HOA factor was minor in AMS datasets collected in remote and rural areas.…”

Airborne observations of IEPOX-derived isoprene SOA in the Amazon during SAMBBA

“…This marker has now been reported in a number of environments using ground-based AMS and ACSM measurements, for example in Canada (Slowik et al, 2011) and downtown Atlanta, GA (Budisulistiorini et al, 2013), consistent with the formation of isoprene SOA through the IEPOX route, although not enough data currently exist to form a universal picture of its behaviour. Tropical environments are of particular interest because of the dominance of isoprene in the biogenic VOC budgets (Guenther et al, 2006) and the often lower anthropogenic influence, resulting in lower NO x concentrations.…”