Geochemical perspectives from a new aerosol chemical mass closure

[摘要] The aerosol chemical mass closure is revisited and a simple and inexpensivemethodology is proposed. This methodology relies on data obtained foraerosol mass, and concentration of the major ions and the two main carboncomponents, the organic carbon (OC) and the black carbon (BC). Atmosphericparticles are separated into coarse (AD>2 μm) and fine (AD<2 μm)fractions and are treated separately. For the coarse fraction thecarbonaceous component is minor and assumption is made for the conversionfactor k of OC-to-POM (Particulate Organic Matter) whichis fixed to the value of 1.8 accounting for secondary species. The coarsesoluble calcium is shown to display a correlation (regressioncoefficient f, y axis intercept b) withthe missing mass. Conversely, the fine fraction is dominated by organicspecies and assumption is made for dust which is assumed to have the samef factor as the coarse mode dust. The fine mode massobtained from chemical analyses is then adjusted to the actual weighed massby tuning the k conversion factor. The kcoefficient is kept different in the two modes due to the expected differentorigins of the organic particles. Using the f and k coefficient obtainedfrom the data set, the mass closure is reached for each individual samplewith an undetermined fraction less than 10%. The procedure has beenapplied to different urban and peri-urban environments in Europe and inBeijing and its efficiency and uncertainties on f andk values are discussed. The f andk coefficients are shown to offer consistent geochemicalindications on aerosol origin and transformations. fallows to retrieve dust mass and its value accounting for Ca abundance indust at the site of investigation may serve as an indicator of dust originand aerosol interactions with anthropogenic acids. f values were found tovary in the 0.08–0.12 range in European urban areas, and a broader range inBeijing (0.01–0.16). As expected, k appears to be arelevant proxy for particle origin and ageing and varies in the 1.4–1.8range. For Beijing, k exhibits high values of about 1.7 inwinter and summer. Winter values suggest that fresh coal aerosol might beresponsible for such a high k value, which was not takeninto account in previous works.

[学科分类] 大气科学