Size distributions, sources and source areas of water-soluble organic carbon in urban background air

Abstract

Abstract. This paper represents the results of one year long measurement period of the size distributions of water-soluble organic carbon (WSOC), inorganic ions and gravimetric mass of particulate matter. Measurements were done at an urban background station (SMEAR III) by using a micro-orifice uniform deposit impactor (MOUDI). The site is located in northern European boreal region in Helsinki, Finland. The WSOC size distribution measurements were completed with the chemical analysis of inorganic ions, organic carbon (OC) and monosaccharide anhydrides from the filter samples. During the measurements gravimetric mass in the MOUDI collections varied between 3.4 and 55.0 μg m−3 and the WSOC concentration was between 0.3 and 7.4 μg m−3. On average, water-soluble particulate organic matter (WSPOM, WSOC multiplied by 1.6) comprised 25±7.7% and 7.5±3.4% of aerosol PM1 mass and the PM1−10 mass, respectively. Inorganic ions contributed 33±12% and 28±19% of the analyzed PM1 and PM1−10 aerosol mass. Five different aerosol categories corresponding to different sources or source areas were identified (long-range transport aerosols, biomass burning aerosols from wild land fires and from small-scale wood combustion, aerosols originating from marine areas and from the clean arctic areas). Clear differences in WSOC concentrations and size distributions originating from different sources or source areas were observed, although there are also many other factors which might affect the results. E.g. the local conditions and sources of volatile organic compounds (VOCs) and aerosols as well as various transformation processes are likely to have an impact on the measured aerosol composition. Using the source categories, it was identified that especially the oxidation products of biogenic VOCs in summer had a clear effect on WSOC concentrations.

Carbonaceous aerosols in Norwegian urban areas

“…The relative contribution of WSOC p to OC p was particularly high at the suburban site, accounting for 79% in winter and 67% in summer. This finding contradicts the general assumption that WSOC is higher in summer compared to winter due to secondary organic aerosol (SOA) formation in summer (Castro et al, 1999;Timonen et al, 2008). During winter the high WSOC p to OC p ratio was consistent with wood burning being the major source, emitting a large number of partly and completely watersoluble compounds, which are lignin, cellulose, and hemicellulose breakdown products (Nolte et al, 2001;Schauer et al, 2001;Fine et al, 2002b;Simoneit, 2002).…”

Chemical Characterization of Summertime Dust Events at Kanpur: Insight into the Sources and Level of Mixing with Anthropogenic Emissions

“…The water soluble organic carbon (WSOC) was analysed with a TOC equipped with a highly sensitive catalyst. The non-purgeable organic carbon method (NPOC) used in the TOC analyser has been described in detail by Timonen et al (2008). Briefly, the sample is extracted with deionised water, acidified and injected into an oven.…”