Abstract
We present results from the international field campaign DAURE (Determination of the sources of atmospheric Aerosols in Urban and Rural Environments in the Western Mediterranean), with the objective of apportioning the sources of fine carbonaceous aerosols. Submicron fine particulate matter (PM1) samples were collected during February-March 2009 and July 2009 at an urban background site in Barcelona (BCN) and at a forested regional background site in Montseny (MSY). We present radiocarbon (C-14) analysis for elemental and organic carbon (EC and OC) and source apportionment for these data. We combine the results with those from component analysis of aerosol mass spectrometer (AMS) measurements, and compare to levoglucosan-based estimates of biomass burning OC, source apportionment of filter data with inorganic composition + EC + OC, submicron bulk potassium (K) concentrations, and gaseous acetonitrile concentrations.
At BCN, 87% and 91% of the EC on average, in winter and summer, respectively, had a fossil origin, whereas at MSY these fractions were 66% and 79%. The contribution of fossil sources to organic carbon (OC) at BCN was 40% and 48%, in winter and summer, respectively, and 31% and 25% at MSY. The combination of results obtained using the C-14 technique, AMS data, and the correlations between fossil OC and fossil EC imply that the fossil OC at Barcelona is similar to 47% primary whereas at MSY the fossil OC is mainly secondary (similar to 85%). Day-to-day variation in total carbonaceous aerosol loading and the relative contributions of different sources predominantly depended on the meteorological transport conditions. The estimated biogenic secondary OC at MSY only increased by similar to 40% compared to the order-of-magnitude increase observed for biogenic volatile organic compounds (VOCs) between winter and summer, which highlights the uncertainties in the estimation of that component. Biomass burning contributions estimated using the C-14 technique ranged from similar to slightly higher than when estimated using other techniques, and the different estimations were highly or moderately correlated. Differences can be explained by the contribution of secondary organic matter (not included in the primary biomass burning source estimates), and/or by an overestimation of the biomass burning OC contribution by the C-14 technique if the estimated biomass burning EC/OC ratio used for the calculations is too high for this region. Acetonitrile concentrations correlate well with the biomass burning EC determined by C-14. K is a noisy tracer for biomass burning.