Abstract
Abstract. Source apportionment of organic aerosol (OA) from aerosol mass spectrometer (AMS) or aerosol chemical speciation monitor (ACSM) measurements relies largely upon mass spectral profiles from different source emissions. However, the changes in mass spectra of primary emissions from AMS–ACSM with the newly developed capture vaporizer (CV) are poorly understood. Here we conducted 21 cooking, crop straw, wood, and coal burning experiments to characterize the mass spectral features of OA and water-soluble OA (WSOA) using SV-AMS and CV-ACSM. Our results show overall similar spectral characteristics between SV-AMS and CV-ACSM for different primary emissions despite additional thermal decomposition in CV, and the previous spectral features for diagnostics of primary OA factors are generally well retained. However, the mass spectral differences between OA and WSOA can be substantial for both SV-AMS and CV-ACSM. The changes in f55 (fraction of m∕z 55 in OA) vs. f57, f44 vs. f60, and f44 vs. f43 in CV-ACSM are also observed, yet the evolving trends are similar to those of SV-AMS. By applying the source spectral profiles to a winter CV-ACSM study at a highly polluted rural site in the North China Plain, the source apportionment of primary OA was much improved, highlighting the two most important primary sources of biomass burning and coal combustion (32 % and 21 %). Considering the rapidly increasing deployments of CV-ACSM and WSOA studies worldwide, the mass spectral characterization has significant implications by providing essential constraints for more accurate source apportionment and making better strategies for air pollution control in regions with diverse primary emissions.
Highlights
Organic aerosol (OA) is ubiquitous in the atmosphere and often contributes a large fraction of aerosol particles
All cooking OA (COA) spectral profiles measured by standard vaporizer (SV)-aerosol mass spectrometer (AMS) and capture vaporizer (CV)-aerosol chemical speciation monitor (ACSM) are highly similar (R2 > 0.89, Fig. 5) and resemble those previously resolved in ambient air during all seasons in Beijing (Fig. S4) despite the fact that COA concentrations can have a difference of an order of magnitude
Considering the rapid increases in deployments of CV-ACSM and the studies on water-soluble OA worldwide, it is of critical importance to further characterize the mass spectra of primary emissions with CVACSM for a better source apportionment of OA in the future
Summary
Organic aerosol (OA) is ubiquitous in the atmosphere and often contributes a large fraction of aerosol particles. The Aerodyne aerosol mass spectrometer (AMS) is one of the most widely used instruments for real-time measurements of OA (Canagaratna et al, 2007; Li et al, 2017). OA can be further separated into primary OA (POA) and secondary OA (SOA) factors by using receptor models, e.g., positive matrix factorization (PMF) and a multilinear engine (ME2) (Paatero, 1999; Paatero and Tapper, 1994). The determination of OA factors relies strongly upon the comparisons with collocated measurements and the mass spectral profiles of primary emissions. In the absence of collocated measurements, the spectral features become the most important constraint for selection of PMF factors. The mass spectra of primary emissions have been extensively characterized with a quadrupole and high-resolution
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