Fossil versus contemporary sources of fine elemental and organic carbonaceous particulate matter during the DAURE campaign in Northeast Spain

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 (PM<sub>1</sub>) 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 (<sup>14</sup>C) 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+EC+OC speciation, submicron bulk potassium (K) concentrations, and gaseous acetonitrile concentrations. <br></br> 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 <sup>14</sup>C technique, AMS data, and the correlations between fossil OC and fossil EC imply that the fossil OC at Barcelona is ~65 % primary whereas at MSY the fossil OC is mainly secondary (~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 ~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 <sup>14</sup>C technique ranged from similar to 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 <sup>14</sup>C 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 <sup>14</sup>C. K is a noisy tracer for biomass burning

Road traffic and sandy playground influence on ambient pollutants in schools

“…This ratio was 0.50 and 1.05 for SC01 and SC17, respectively. Since NO x is a well-known proxy for road traffic contribution to ambient PM (Minguill on et al, 2012), this indicates that, as expected due to the specific location, the overall influence of road traffic was clearly higher at SC17, compared to the rest of the schools. This was further evidenced by the higher BC concentrations, which were 1.5 times higher at SC17 that at the PR reference site, whereas they were similar at SC07 and PR.…”

“…Nevertheless, as discussed later in detail, the influence of the resuspension from the sandy playground on the ambient concentrations in the schools facilities is very local. EC and OM concentrations, which can be mostly attributed to road traffic in the Barcelona urban environment (Minguill on et al, 2011), were measured in similar concentrations at the first pair of schools, whereas the second pair of schools shows a higher influence of road traffic at SC17 than at SC01. Again, the road traffic origin of these variations is supported by the differences weekdayeweekend, which are evident at all four schools.…”

“…Mineral Na was calculated as 0.148*Al 2 O 3 , according to the mineral composition of the PM 2.5 fraction of the analysed school sands (see Section 3.4). OM was estimated as 1.6*OC, assuming an intermediate degree of OC oxidation between primary traffic OC and biomass burning or secondary OC (Aiken et al, 2008), and as previously determined for Barcelona (Minguill on et al, 2011). Sea salt was estimated from the sea-salt Na concentrations (Na ss , resulting from the subtraction of mineral Na from total Na) as 3.235*Na ss , based on standard sea water composition, including Cl À , Mg, SO 2À 4 , Ca and K (M esz aros, 1999).…”

Chemical composition of PM2.5 in an urban environment in Chengdu, China: Importance of springtime dust storms and biomass burning

“…Watson et al (2001) reported OC/EC ratios for coal combustion, vehicle emissions, and biomass burning with values of 2.7, 1.1, and 9.0, respectively. A recent examination of OC/EC ratios for different biomass burning sources revealed a wide range of values from 0.005 to 111, depending on the type of biomass (Minguillón et al, 2011). However, agricultural biomass burning was typically characterized by higher OC/EC ratios (>3.0) in Asia (Ryu et al, 2007;Engling et al, 2009Engling et al, , 2012.…”

Carbonaceous Particles

“…Recent work has combined carbon isotope and mass fragment measurements in another example of recent atmospheric measurements (Minguillon et al, 2011). Radiocarbon measurements ( 14 C/ 12 C) provide a way to distinguish the fraction of carbonaceous particle mass derived from fossil sources (namely, fossil fuel evaporation and partial combustion) and those recently formed from nonfossil sources (namely, marine and terrestrial organic carbon), since fossil carbon contains no measureable 14 C, whereas modern plants contain significant amounts due to ongoing production in the atmosphere by cosmic rays and residual 14 C from nuclear weapons testing that mostly ended in the 1960s.…”