Abstract
Abstract. Aerosol chemical speciation monitor (ACSM) measurements were performed in Zurich, Switzerland, for 13 months (February 2011 through February 2012). Many previous studies using this or related instruments have utilized the fraction of organic mass measured at m/z 44 (f44), which is typically dominated by the CO2+ ion and related to oxygenation, as an indicator of atmospheric aging. The current study demonstrates that during summer afternoons, when photochemical processes are most vigorous as indicated by high oxidant – OX (O3 + NO2), f44 for ambient secondary organic aerosol (SOA) is not higher but is rather similar or lower than on days with low OX. On the other hand, f43 (less oxidized fragment) tends to increase. These changes are discussed in the f44 / f43 space frequently used to interpret ACSM and aerosol mass spectrometer (AMS) data. This is likely due to the formation of semi-volatile oxygenated aerosol produced from biogenic precursor gases, whose emissions increase with ambient temperature. In addition, source apportionment analyses conducted on winter and summer data using positive matrix factorization (PMF) yield semi-volatile oxygenated organic aerosol (SV-OOA) factors that retain source-related chemical information. Winter SV-OOA is highly influenced by biomass burning, whereas summer SV-OOA is to a high degree produced from biogenic precursor gases. These sources contribute to substantial differences between the winter and summer f44 / f43 data, suggesting that PMF analysis of multi-season data employing only two OOA factors cannot capture the seasonal variability of OOA.
Highlights
Atmospheric aerosols are at the center of scientific and political discussions due to their highly uncertain direct and indirect climate effects (IPCC, 2007), their adverse impacts on human health (Peng et al, 2005), and their influence on our inhabited (Watson, 2002) and agricultural areas (Matson et al, 2002)
The approach used in this study for estimating f43 and f44 for OOA involved the subtraction of the contributions from the primary sources arising at m/z 43 and m/z 44
Note that the solutions are environmentally reasonable: the traffic factor correlates with NOx and equivalent black carbon (EBC), the cooking factor peaks during mealtimes, BBOA is higher at night and lower during the day accounting for nocturnal heating in winter and barbecuing and possible local fire events in summer, and the daily cycle of SV-OOA is anticorrelated with temperature for the winter and summer data
Summary
Atmospheric aerosols are at the center of scientific and political discussions due to their highly uncertain direct and indirect climate effects (IPCC, 2007), their adverse impacts on human health (Peng et al, 2005), and their influence on our inhabited (Watson, 2002) and agricultural areas (Matson et al, 2002). Aerodyne aerosol mass spectrometers (AMS), including the aerosol chemical speciation monitor (ACSM), have become important and widely employed instruments for the chemical characterization of submicron organic aerosol (OA) (Canagaratna et al, 2007; Ng et al, 2011b). These instruments provide online quantitative mass spectra of the non-refractory (inorganic and organic) aerosol composition with high time resolution. The ambient studies showing the raw data points consider the total f43 and f44 fraction rather than the model-derived OOA. The OOA composition is characterized in terms of f44 and f43, investigating the extent to which precursor sources can be inferred from these values
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
