Abstract
Abstract. Long-term monitoring of organic aerosol is important for epidemiological studies, validation of atmospheric models, and air quality management. In this study, we apply a recently developed filter-based offline methodology using an aerosol mass spectrometer (AMS) to investigate the regional and seasonal differences of contributing organic aerosol sources. We present offline AMS measurements for particulate matter smaller than 10 µm at nine stations in central Europe with different exposure characteristics for the entire year of 2013 (819 samples). The focus of this study is a detailed source apportionment analysis (using positive matrix factorization, PMF) including in-depth assessment of the related uncertainties. Primary organic aerosol (POA) is separated in three components: hydrocarbon-like OA related to traffic emissions (HOA), cooking OA (COA), and biomass burning OA (BBOA). We observe enhanced production of secondary organic aerosol (SOA) in summer, following the increase in biogenic emissions with temperature (summer oxygenated OA, SOOA). In addition, a SOA component was extracted that correlated with an anthropogenic secondary inorganic species that is dominant in winter (winter oxygenated OA, WOOA). A factor (sulfur-containing organic, SC-OA) explaining sulfur-containing fragments (CH3SO2+), which has an event-driven temporal behaviour, was also identified. The relative yearly average factor contributions range from 4 to 14 % for HOA, from 3 to 11 % for COA, from 11 to 59 % for BBOA, from 5 to 23 % for SC-OA, from 14 to 27 % for WOOA, and from 15 to 38 % for SOOA. The uncertainty of the relative average factor contribution lies between 2 and 12 % of OA. At the sites north of the alpine crest, the sum of HOA, COA, and BBOA (POA) contributes less to OA (POA / OA = 0.3) than at the southern alpine valley sites (0.6). BBOA is the main contributor to POA with 87 % in alpine valleys and 42 % north of the alpine crest. Furthermore, the influence of primary biological particles (PBOAs), not resolved by PMF, is estimated and could contribute significantly to OA in PM10.
Highlights
The development and field deployment of the Aerodyne aerosol mass spectrometer (AMS; Canagaratna et al, 2007) have greatly improved air quality monitoring by providing real-time measurements of the non-refractory (NR) submicron aerosol (PM1) components
Factors typically extracted include directly emitted primary organic aerosol (OA) (POA) from biomass burning (BBOA) or traffic (HOA), and oxygenated OA (OOA) that is typically associated with secondary OA (SOA), formed through the oxidation of organic vapour precursors or heterogeneous processes
The fraction of oxygenated organic fragments that were missing in the initial reference profile, which were added based on unit mass resolution (UMR) spectra, show an increased contribution to the ions above m/z = 100
Summary
The development and field deployment of the Aerodyne aerosol mass spectrometer (AMS; Canagaratna et al, 2007) have greatly improved air quality monitoring by providing real-time measurements of the non-refractory (NR) submicron aerosol (PM1) components. Most available datasets are often limited to a few weeks of measurements, and factors are extracted mainly based on diurnal variations in POA emission strength and SOA oxygen content (Zhang et al, 2011; El Haddad et al, 2013). Mohr et al, 2011) are designed for regional studies, but are even more limited by cost, availability, and time than stationary studies. This hinders the determination of the aerosol regional and seasonal characteristics and evaluation of long-term emission trends, limiting the information required for model validation and development of efficient mitigation strategies. The negligible transmission efficiency of the AMS inlet for coarse particles prevents the characterization of their chemical nature and contributing sources
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