The regional aerosol in eastern central china and its cloud microphysical and optical properties of haze at high relative humidities
Zusammenfassung der Projektergebnisse
The results of HaChi project provide for the first time hygroscopic growth and state of mixing at high relative humidities combined with cloud activation for the regional aerosol over the North China Plain using the unique instruments HH-TDMA and LACIS-mobile. LACIS thereby bridges HH-TDMA and CCN data and allows determining the κ-value over a wide RH range. These measurements were complemented by particle number size distribution, light scattering and absorption measurements as well as the chemical characterization of the near ground aerosol. For the first time, hygroscopic growth was measured of particles in the size range 50-250 nm for relative humidities up to approximately 99% using a HHTDMA in field. In early spring the hygroscopic growth is dominated by ammonium sulfate and ammonium nitrate and in summer mainly by ammonium sulfate, reaching growth factors of 3.0 and 3.9 for 250 nm particles near saturation, respectively. It was found that κ changed with RH, which means that the atmospheric aerosol particlewater solution did not behave ideally. These results are of great importance to understand the regional haze and its influence on the direct climate forcing of the aerosol. A parameterization of the hygroscopic growth for different sizes was developed, which could improve regional climate models. Near ground, hydrophobic particles have a strong diurnal variation. This fraction reaches 20% during night, which is reduced the air quality in terms of toxicity of the aerosol. The monodisperse activation measurements allowed for the determination of CCN spectra and κvalues in a highly polluted area, now available for application in modeling studies. By means of a newly developed iteration scheme the surface tension of the droplets was determined. A reduction compared to that of pure water of approx. 10% was observed. The occurrence of low visibility events is frequent in the North China Plain. High aerosol volume concentration is responsible for low visibility at RH<90%; while for RH>90%, decrease of visibility is mainly influenced by the increase of RH, e.g. the strong hygroscopicity of aerosol. A parameterization of ambient aerosol extinction coefficient was developed on the basis of aerosol volume concentrations and RH. Usually significantly higher PM1 masses and sulfate fractions are observed on hazy than on clear days, while the carbon fractions, especially the EC, are inversely distributed, indicating a dominating anthropogenic photochemical influence on the haze formation. One major unexpected result was that the hygroscopic growth of the regional aerosol (hygroscopic mode) is mainly determined by inorganic salts and less influenced by organic aerosol compounds. For larger hygroscopic particles of 250 nm size, LACIS-mobile and the HH-TMDA detected high hygroscopic growth and κ-values of about 0.47 (at 99% RH)., i.e. values close to those of ammonium sulfate which features a κ of 0.53. It is remarkable that no significant correlation was found between κ and the CCN number concentration. This can be attributed to the observed low variability in κ, but more important to the critical supersaturation for droplet activation being more sensitive to particle size than to particle hygroscopicity.
Projektbezogene Publikationen (Auswahl)
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(2011). Aerosol optical properties in the North China Plain during HaChi campaign: an in-situ optical closure study. Atmos. Chem. Phys., 11, 5959-5973
N. Ma, C. S. Zhao, A. Nowak, T. Müller, S. Pfeifer, Y. F. Cheng, Z.Z. Deng, P. F. Liu, W. Y. Xu, L. Ran, P. Yan, T. Göbel, E. Hallbauer, K. Mildenberger, S. Henning, J. Yu, L. L. Chen, X. J. Zhou, F. Stratmann, and A. Wiedensohler
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(2011). Characteristics of pollutants and their correlation to meteorological conditions at a suburban site in the North China Plain. Atmos. Chem. Phys., 11, 4353-4369
W. Y. Xu, C. S. Zhao, L. Ran, Z. Z. Deng, P. F. Liu, N. Ma, W. L. Lin, X. B. Xu, P. Yan, X. He, J. Yu, W. D. Liang, and L. L. Chen
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(2011). Hygroscopic properties of aerosol particles at high relative humidity and their diurnal variations in the North China Plain. Atmos. Chem. Phys., 11, 3479-3494
P. F. Liu, C. S. Zhao, T. Göbel, E. Hallbauer, A. Nowak, L. Ran, W. Y. Xu, Z. Z. Deng, N. Ma, K. Mildenberger, S. Henning, F. Stratmann, and A. Wiedensohler
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(2011). Size-resolved and bulk activation properties of aerosols in the North China Plain. Atmos. Chem. Phys., 11, 3835-3846
Z. Z. Deng, C. S. Zhao, N. Ma, P. F. Liu, L. Ran, W. Y. Xu, J. Chen, Z. Liang, S. Liang, M. Y. Huang, X. C. Ma, Q. Zhang, J. N. Quan, P. Yan, S. Henning, K. Mildenberger, E. Sommerhage, M. Schäfer, F. Stratmann, and A. Wiedensohler
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(2012). A new method to determine the mixing state of light absorbing carbonaceous using the measured aerosol optical properties and number size distributions. Atmos. Chem. Phys., 12, 2381-2397
N. Ma, C. S. Zhao, T. Müller, Y. F. Cheng, P. F. Liu, Z. Z. Deng, W. Y. Xu, L. Ran, B. Nekat, D. van Pinxteren, T. Gnauk, K. Müller, H. Herrmann, P. Yan, X. J. Zhou, and A. Wiedensohler
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(2012). A parameterization of low visibilities for hazy days in the North China Plain. Atmos. Chem. Phys., 12, 4935-4950
J. Chen, C. S. Zhao, N. Ma, P. F. Liu, T. Göbel, E. Hallbauer, Z. Z. Deng, L. Ran, W. Y. Xu, Z. Liang, H. J. Liu, P. Yan, X. J. Zhou, and A. Wiedensohler
