Evolution of aerosol optical thickness over Europe during the August 2003 heat wave as seen from CHIMERE model simulations and POLDER data

[摘要] This study describes the atmospheric aerosol load encountered during thelarge-scale pollution episode that occurred in August 2003, by means of theaerosol optical thicknesses (AOTs) measured at 865 nm by the Polarizationand Directionality of the Earth's Reflectances (POLDER) sensor and thesimulation by the CHIMERE chemistry-transport model. During this period manyprocesses (stagnation, photochemistry, forest fires) led to unusually highparticle concentrations and optical thicknesses. The observed/simulated AOTcomparison helps understanding the ability of the model to reproduce most ofthe gross AOT features observed in satellite data, with a general agreementwithin a factor 2 and correlations in the 0.4–0.6 range. However someimportant aerosol features are missed when using regular anthropogenicsources. Additional simulations including emissions and high-altitudetransport of smoke from wildfires that occurred in Portugal indicate thatthese processes could dominate the AOT signal in some areas. Our resultsalso highlight the difficulties of comparing simulated and POLDER-derivedAOTs due to large uncertainties in both cases. Observed AOT values aresignificantly lower than the simulated ones (30–50%). Their comparisonwith the ground-based Sun photometer Aerosol Robotic Network (AERONET)measurements suggests, for the European sites considered here, anunderestimation of POLDER-derived aerosol levels with a factor between 1 and2. AERONET AOTs compare better with simulations (no particular bias) thanPOLDER AOTs.

[学科分类] 大气科学