Biomass burning contributions to urban aerosols in a coastal Mediterranean City

Mean annual biomass burning contributions to the bulk particulate matter (PMX) load were quantified in a southern-European urban environment (Barcelona, Spain) with special attention to typical Mediterranean winter and summer conditions. In spite of the complexity of the local air pollution cocktail and the expected low contribution of biomass burning emissions to PM levels in Southern Europe, the impact of these emissions was detected at an urban background site by means of tracers such as levoglucosan, K+ and organic carbon (OC). The significant correlation between levoglucosan and OC (r2 = 0.77) and K+ (r2 = 0.65), as well as a marked day/night variability of the levoglucosan levels and levoglucosan/OC ratios was indicative of the contribution from regional scale biomass burning emissions during night-time transported by land breezes. In addition, on specific days (21–22 March), the contribution from long-range transported biomass burning aerosols was detected.Quantification of the contribution of biomass burning aerosols to PM levels on an annual basis was possible by means of the Multilinear Engine (ME). Biomass burning emissions accounted for 3% of PM10 and PM2.5 (annual mean), while this percentage increased up to 5% of PM1. During the winter period, regional-scale biomass burning emissions (agricultural waste burning) were estimated to contribute with 7 ± 4% of PM2.5 aerosols during night-time (period when emissions were clearly detected). Long-range transported biomass burning aerosols (possibly from forest fires and/or agricultural waste burning) accounted for 5 ± 2% of PM2.5 during specific episodes. Annually, biomass burning emissions accounted for 19%–21% of OC levels in PM10, PM2.5 and PM1. The contribution of this source to K+ ranged between 48% for PM10 and 97% for PM1 (annual mean). Results for K+ from biomass burning evidenced that this tracer is mostly emitted in the fine fraction, and thus coarse K+ could not be taken as an appropriate tracer of biomass burning.

► We identify the biomass burning impact to PM levels in a Mediterranean urban site.
► It was possible by specific tracers: levoglucosan, K+ and OC.
► The PMF (ME-2) model allowed the quantification of biomass burning contribution to PM levels.
► Biomass burning emissions accounted for 3% of the annual PM10 and PM2.5 and 5% of PM1.
► Biomass burning emission contribution to OC levels was constant among PM fractions.