Characterization and parameterization of atmospheric particle number‐, mass‐, and chemical‐size distributions in central Europe during LACE 98 and MINT

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Abstract
Intensive measurements of chemical and physical properties of the atmospheric aerosol have been performed at two sites in central Europe during the Melpitz‐Intensive (MINT) in November 1997 and the Lindenberg Aerosol Characterization Experiment 1998 (LACE 98) in July and August 1998. Number‐size distributions, hygroscopic particle growth, size‐segregated gravimetric mass, and size‐segregated chemical masses of water‐soluble ions and organic and elemental carbon of aerosol particles have been measured. To obtain information on the quality of the different methods, the number‐derived, gravimetric, and chemically derived mass distributions are compared. Gravimetric mass of fine particles is attributed completely to chemical composition by carbonaceous material and ions, including an estimate of the water content due to hygroscopic compounds. For the characterization of coarse particles, which contribute less to the total mass concentration, insoluble material has to be included in the mass balance. Mass concentrations calculated from the number‐size distributions are well correlated with the gravimetric mass concentration; however, the calculated mass is larger, especially for the Aitken and accumulation modes. The number‐derived mass concentration is most sensitive to the sizing uncertainty of the measured number‐size distribution. Moreover, the impactor cutoffs and the limited knowledge about the density of the particles (especially with high carbon content) account for a major part of the uncertainties. The overall uncertainty of the calculated mass, determined as the standard deviation of the average value in a Monte Carlo approach, is found to be about 10%. Lognormal parameters for the number‐size and volume‐size distributions as well as gravimetric mass‐size distribution and corresponding chemical composition are presented for different air mass types. Most of the modal parameters do not differ significantly between the air mass types. Higher mass concentrations are mostly due to an increase in size (of Aitken and accumulation mode) rather than an increase in the number of particles in a given mode. Generally, the mass percent carbon content increases with decreasing particle size. The most pronounced difference with season is an increase of carbon content from summer to winter as well as an increase in nitrate content, resulting in a decrease of sulfate. For nitrate a strong dependence on air mass direction is observed. Sulfate and nitrate are predominantly neutralized by ammonium. With the results of the two experiments, quality‐controlled mode parameters and corresponding chemical composition of atmospheric aerosol particles in central Europe are now available for application in models.

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