Size distribution of EC and OC in the aerosol of Alpine valleys during summer and winter

[摘要] Collections of samples were conducted for the determination of the sizedistributions of EC and OC during the intensive sampling campaigns of thePOVA program, in two Alpine valleys of the French Alps, in summer and inwinter. The comparison of concentrations obtained for samples collected inparallel with impactor- and filter-based methods is rather positive withslopes of 0.95 and 0.76 for OC and EC, respectively and correlations closeto 1 (0.92 and 0.90 for OC and EC, respectively, n=26). This is anindication that the correction of pyrolysis seems to work for the impactorsamples despite non even deposits. The size distributions of theconcentrations of EC and OC present large evolutions between winter andsummer, and between a suburban and a rural site. In winter, an overwhelmingproportion of the mass fraction of both species is found in the droplet andaccumulation modes, often (but not always) in association with sulfate andother chemical species resulting from secondary formation processes. Someindications of gas/particles exchanges can be found for the other parts ofthe size spectrum (the Aitken and super micron modes) in the case of therural site. In summer, the changes are more drastic with, according to thecase, a dominant droplet or accumulation mode. Particularly at the ruralsite, the large extent of processing of the aerosol due to gas/particlesexchanges is evident for the Aitken and super micron modes, with increasingof the OC mass fractions in these size ranges. All of these observationsgive indications on the degree of internal vs. external mixing of thespecies investigated in the different modes.

[学科分类] 大气科学