Estimating contributions from biomass burning, fossil fuel combustion, and biogenic carbon to carbonaceous aerosols in the Valley of Chamonix: a dual approach based on radiocarbon and levoglucosan

Abstract

DOI des données supplémentaires : 10.5194/acp-16-13753-2016-supplementInternational audienceAtmospheric particulate matter (PM) affects the climate in various ways and has a negative impact on human health. In populated mountain valleys in Alpine regions , emissions from road traffic contribute to carbonaceous aerosols, but residential wood burning can be another source of PM during winter. We determine the contribution of fossil and non-fossil carbon sources by measuring radiocarbon in aerosols using the recently installed AixMICADAS facility. The accelerator mass spectrometer is coupled to an elemental analyzer (EA) by means of a gas interface system directly connected to the gas ion source. This system provides rapid and accurate radiocarbon measurements for small samples (10–100 µgC) with minimal preparation from the aerosol filters. We show how the contamination induced by the EA protocol can be quantified and corrected for. Several standards and synthetic samples are then used to demonstrate the precision and accuracy of aerosol measurements over the full range of expected 14 C / 12 C ratios, ranging from modern carbon to fossil carbon depleted in 14 C. Aerosols sampled in Chamonix and Passy (Arve River valley , French Alps) from November 2013 to August 2014 are analyzed for both radiocarbon (124 analyses in total) and lev-oglucosan, which is commonly used as a specific tracer for biomass burning. NO x concentration, which is expected to be associated with traffic emissions, is also monitored. Based on 14 C measurements, we can show that the relative fraction of non-fossil carbon is significantly higher in winter than in summer. In winter, non-fossil carbon represents about 85 % of total carbon, while in summer this proportion is still 75 % considering all samples. The largest total carbon and levoglucosan concentrations are observed for winter aerosols with values up to 50 and 8 µg m −3 , respectively. These levels are higher than those observed in many European cities, but are close to those for other polluted Alpine valleys. The non-fossil carbon concentrations are strongly correlated with the levoglucosan concentrations in winter samples, suggesting that almost all of the non-fossil carbon originates from wood combustion used for heating during winter. For summer samples, the joint use of 14 C and levoglucosan measurements leads to a new model to separately quantify the contributions of biomass burning and biogenic emissions in the non-fossil fraction. The comparison of the biogenic fraction with polyols (a proxy for primary soil biogenic emissions) and with the temperature suggests a major influence of the secondary biogenic aerosols. Significant correlations are found between the NO x concentration and the fossil carbon concentration for all seasons and sites, confirming the relation between road traffic emissions and fossil carbon. Overall, this dual approach combining radiocarbon and levoglucosan analyses strengthens the conclusion concerning Published by Copernicus Publications on behalf of the Eur...

Source apportionment of carbonaceous chemical species to fossil fuel combustion, biomass burning and biogenic emissions by a coupled radiocarbon–levoglucosan marker method

“…A further important uncertainty can arise from a variable OC / LVG conversion factor of 5.59 due to spatially and temporally changing burning conditions. The overall relative contributions are in very good agreement with other wintertime urban atmospheric studies (Szidat et al, 2009, and references therein;Minguillón et al, 2011;Bernardoni et al, 2013;Bonvalot et al, 2016).…”

“…The relative contributions of EC and OC to the TC derived directly from the measured atmospheric concentrations were combined with the results of the independent radiocarbon and LVG marker models regarding the fossil, contemporary (non-fossil) and BB sources in a coupled approach (see also Bonvalot et al, 2016) on a sample-bysample basis. The novel source apportionment scheme of the TC into the contributions of EC and OC from FF combustion (EC FF and OC FF , respectively), EC and OC from BB (EC BB and OC BB , respectively), and OC from biogenic sources (OC BIO ) proposed and utilized in the present study is summarized in Fig.…”

Comparison between five acellular oxidative potential measurement assays performed with detailed chemistry on PM<sub>10</sub> samples from the city of Chamonix (France)

“…During the cold period, traffic tracers or indicators (like Cu, Fe, Mo, Ti, or ∑ PAHs) are important 15 positive factors to explain all OP measurements. Also, and with the exception of the ESR assay, biomass burning tracers (∑ Monosaccharides, including levoglucosan) or indicators such as ∑ PAHs or OC* (corresponding to total OC minus the molecular species measured) both strongly related to biomass burning emission (Bonvalot et al, 2016;Chevrier, 2016), are prominent positive factors for all assays for this cold period. These results agree with the observations on the seasonal evolution of OPv, with much larger values in the cold period when biomass burning emissions are dominant.…”

Evolution of the chemical fingerprint of biomass burning organic aerosol during aging

“…Levoglucosan, for instance, is a commonly emitted tracer of biomass burning. Its ubiquity and abundance (Waked et al, 2014;Bonvalot et al, 2016;Maenhaut et al, 2016) have been used to demonstrate the significant contribution of biomass burning to the total organic aerosol source globally (Robinson et al, 2006;Gelencsér et al, 2007;Puxbaum et al, 2007;Stone et al, 2010;Crippa et al, 2013). 20 The concentration of organic aerosol (OA) particle mass has been documented to increase up to 7 times during photochemical aging (Grieshop et al, 2009;Heringa et al, 2011;Ortega et al, 2013;Bruns et al, 2015;Tiitta et al, 2016), however, the chemical composition of this secondary organic aerosol (SOA) produced remains uncertain.…”