Sources of organic carbon in fine particulate matter in northern European urban air

Abstract

Abstract.A major fraction of fine particle matter consists of organic carbon (OC) but its origin is still inadequately known. In this study the sources of OC were investigated in the northern European urban environment in Helsinki, Finland. Measurements were carried out over one year and they included both filter (PM 1 ) and online methods. From the filter samples OC, elemental carbon (EC), water-soluble OC (WSOC), levoglucosan and major ions were analyzed. Filter data together with the concentrations of inorganic gases were analyzed by Positive matrix factorization (PMF) in order to find the sources of OC (and WSOC) on an annual as well as on a seasonal basis. In order to study the diurnal variation of sources, OC and EC were measured by a semicontinuous OC/EC analyzer and major ions were determined by a Particle-into-Liquid Sampler coupled to ion chromatographs. According to PMF, OC concentrations were impacted by four sources: biomass combustion, traffic, long-range transport and secondary production. On an annual basis the OC concentration was dominated by secondary organic aerosol (SOA). Its contribution to OC was as high as 64% in summer, which besides anthropogenic sources may also result from the large biogenic volatile organic carbon (VOC) emissions in the boreal region. In winter biomass combustion constituted the largest fraction in OC due to domestic wood combustion for heating purposes. Traffic contributed to OC from 15 to 27%. Regarding the diurnal variation, the contribution from traffic was higher from 08:00 to 18:00 on weekdays than on weekends. The contribution from long-range transport to OC was 24% on average. All four sources also influenced the WSOC concentrations, however, the contribution of SOA was significantly larger for WSOC than OC.

Characterization of carbonaceous aerosols over the East China Sea: The impact of the East Asian continental outflow

“…Relatively high OC/EC ratios were reported to be associated with biomass burning ; whereas lower ratios were observed to characterize vehicle emissions (Saarikoski et al, 2008). In the present study, the average OC/EC ratios in PM2.5 were highest in summer (6.0) and lowest in spring (2.8).…”

Water-soluble organic carbon (WSOC) and its temperature-resolved carbon fractions in atmospheric aerosols in Beijing

“…For example, roadside measurements in Paris showed a value of 0.12 for WSOC/OC (Ruellan and Cachier, 2001), while WSOC/OC ratios were reported to be ranged from 0.40 to 0.45 in aerosols collected during peak of biomass burning season in the Brazilian Amazon region (MayolBracero et al, 2002). Other evidence was provided by Saarikoski et al (2008), who reported the value of 0.27 for vehicular emissions over an urban environment in Helsinki, in contrast to the value of 0.4 for biomass burning. It is generally acknowledged that WSOC/OC ratios are relatively high in SOA aerosol (Saxena and Hildemann, 1996), as confirmed by the study of Saarikoski et al (2008), who reported that WSOC/OC ratio had a value of 0.8 for secondary organic aerosol.…”

“…Other evidence was provided by Saarikoski et al (2008), who reported the value of 0.27 for vehicular emissions over an urban environment in Helsinki, in contrast to the value of 0.4 for biomass burning. It is generally acknowledged that WSOC/OC ratios are relatively high in SOA aerosol (Saxena and Hildemann, 1996), as confirmed by the study of Saarikoski et al (2008), who reported that WSOC/OC ratio had a value of 0.8 for secondary organic aerosol. Therefore, it is likely a reasonable assumption that the enhanced WSOC/OC ratios suggest the contribution of secondary formation or biomass burning emissions, while low WSOC/OC ratios indicate the contribution of vehicular emissions.…”

High time-resolution chemical characterization of the water-soluble fraction of ambient aerosols with PILS-TOC-IC and AMS

“…The PILS is typically coupled with either ion chromatograph or total organic carbon analyzer (e.g. Kondo et al, 2007;Saarikoski et al, 2008). Examples of the previous measurement campaigns, where PILS has been used, are collected to Table 1.…”

“…biomass combustion, secondary aerosol formation, long-range transport and in-cloud processing (Huang et al, 2006;Viana et al, 2007;Saarikoski et al, 2008). Biomass burning and secondary organic aerosol (SOA) formation are considered to be the major sources of WSOC Kondo et al, 2007).…”