Abstract
Winter and summer measurements of organic carbon and elemental carbon (OC and EC) in PM2.5 were performed in parallel at two sites, the rural background station Kosetice and the Prague-Suchdol urban background site, with a 2-h time resolution using semi-online field OC/EC analysers.
Seasonal and site differences were found in the OC and EC contents of PM2.5. Overall, the highest concentrations of both OC and ECwere duringwinter at the urban site. The average urban impactwas 50% for OC and 70% for EC. The summer season gives similar concentrations of OC at both sites. However, higher concentrations of EC, caused by higher traffic, were found at the urban site with an average urban increase of 50%. Moreover, an analysis of four OC fractions depending on the volatility (OC1 - most volatile, OC4 - least volatile) and pyrolytic carbon (PC) is provided. A similar level of each OC fraction at both sites was found in summer, except for higher OC1 at urban and higher PC at the rural site. Inwinter, the differences between the urban and rural siteswere dominated by a large increase of theOC1 fraction in comparisonwith the rural site. A diurnal pattern of concentration and share of OC1 and PC suggests a prevailing influence of local sources on their concentrations at the urban site in winter. The OC3 and OC4 diurnal cycles suggest their more regional or long range transport origin in both seasons.
The prevalent influence of OC1 at any urban site has not been previously reported. The minimisation of semi-volatile carbon losses during semi-continuous sampling and analysis, in comparison with off-line sampling methods, is a probable reason for the observed differences. (C) 2015 Elsevier B.V. All rights reserved.