Atmospheric Organic Aerosol Age Distribution over Europe during a Period with Intense Wildfires

Abstract

The age of particulate matter (PM), focusing on organic aerosols, was estimated during a summer period with severe wildfires in Europe, combining a chemical transport model (CTM) with a computationally efficient source apportionment algorithm. The organic components of PM were highly aged, especially when they originated from wildfires. The average age of organic aerosol (OA) at the ground level above Europe was 58 h, while the average age of biomass burning organic aerosol (bbOA) was 86 h, and that of non-bbOA was 49 h. The average age of OA was different for OA species with different volatilities. As the volatility of the OA components decreased, their average age increased. The average age of the semivolatile biomass burning secondary OA was 66 h, while that of low volatility biomass burning secondary OA was 95 h. These results suggest that the OA to which the population of Europe is exposed is quite different due to aging physical and chemical processes from the particles emitted by its various sources. The average age of OA was found to decrease when the OH levels increased and vice versa. A reduction of the aging rate by an order of magnitude resulted in a 45% increase in the average age of anthropogenic secondary OA. On the other hand, 10 times faster aging reactions resulted in a 20% decrease in the average age of anthropogenic secondary organic aerosol. These changes resulted in minor changes in the average age of the primary organic aerosol.