Characterization of aerosol particle episodes in Finland caused by wildfires in Eastern Europe

[摘要] We studied the sources, compositions and size distributions of aerosolparticles during long-range transport (LRT) PM_2.5 episodes whichoccurred on 12–15 August, 26–28 August and 5–6 September 2002 in Finland. Backward air masstrajectories, satellite detections of fire areas and dispersion modellingresults indicate that emissions from wildfires in Russia and other EasternEuropean countries arrived in Finland during these episodes. Elementalanalyses using scanning electron microscopy (SEM) coupled with energydispersive X-ray microanalyses (EDX) showed that the proportions of S-richparticles and agglomerates (agglomeration was caused partly by the samplingmethod used) increased during the episodes, and they contained elevatedfractions of K, indicating emissions from biomass burning. These aerosolswere mixed with S-rich emissions from fossil fuel burning during transportsince air masses came through polluted areas of Europe. Minor amounts ofcoarse Ca-rich particles were also brought by LRT during the episodes, andthey probably originated from wildfires and/or from Estonian and Russianoil-shale-burning industrial areas. Ion chromatography analysis showed thatconcentrations of sulphate (SO₄^2-), total nitrate (NO₃^-+HNO₃(g))and total ammonium (NH₄⁺+NH₃(g)) increasedduring the episodes, but the ratio of the total amount of these ions toPM₁₀ concentration decreased, indicating unusually high fractions ofother chemical components. Particle number size distribution measurementswith differential mobility particle sizer (DMPS) revealed thatconcentrations of particles 90–500 nm increased during the episodes, whileconcentrations of particles smaller than 90 nm decreased. The reduction ofthe smallest particles was caused by suppressed new particle formation dueto vapour and molecular cluster uptake of LRT particles. Our results showthat emissions from wildfires in Russian and other Eastern Europeancountries deteriorated air quality of very large areas, even at distances ofover 1000 km from the fire areas.

[学科分类] 大气科学