Journal Article

PreJuSER-20027

http://join2-wiki.gsi.de/foswiki/pub/Main/Artwork/join2_logo100x88.png Comparison of ambient aerosol extinction coefficients obtained from in-situ, MAX-DOAS and LIDAR measurements at Cabauw

Zieger, P. ; Weingartner, E. ; Henzing, J. ; Moerman, M. ; de Leeuw, G. ; Mikkilä, J. ; Ehn, M.FZJ* ; Petäjä, T. ; Clemer, K. ; van Roozendael, M. ; Yilmaz, S. ; Frieß, U. ; Irie, H. ; Wagner, T. ; Shaiganfar, R. ; Beirle, S. ; Apituley, A. ; Wilson, K. ; Baltensperger, U.

2011
EGU Katlenburg-Lindau

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Please use a persistent id in citations: http://hdl.handle.net/2128/9941  doi:10.5194/acp-11-2603-2011

Abstract: In the field, aerosol in-situ measurements are often performed under dry conditions (relative humidity RH < 30-40%). Since ambient aerosol particles experience hygroscopic growth at enhanced RH, their microphysical and optical properties - especially the aerosol light scattering are also strongly dependent on RH. The knowledge of this RH effect is of crucial importance for climate forcing calculations or for the comparison of remote sensing with in-situ measurements. Here, we will present results from a four-month campaign which took place in summer 2009 in Cabauw, The Netherlands. The aerosol scattering coefficient sigma(sp)(lambda) was measured dry and at various, predefined RH conditions between 20 and 95% with a humidified nephelometer. The scattering enhancement factor f (RH,lambda) is the key parameter to describe the effect of RH on sigma(sp)(lambda) and is defined as sigma(sp)(RH,lambda) measured at a certain RH divided by the dry sigma(sp)(dry,lambda). The measurement of f (RH,lambda) together with the dry absorption measurement (assumed not to change with RH) allows the determination of the actual extinction coefficient sigma(ep)(RH,lambda) at ambient RH. In addition, a wide range of other aerosol properties were measured in parallel. The measurements were used to characterize the effects of RH on the aerosol optical properties. A closure study showed the consistency of the aerosol in-situ measurements. Due to the large variability of air mass origin (and thus aerosol composition) a simple parameterization of f (RH,lambda) could not be established. If f (RH,lambda) needs to be predicted, the chemical composition and size distribution need to be known. Measurements of four MAX-DOAS (multi-axis differential optical absorption spectroscopy) instruments were used to retrieve vertical profiles of sigma(ep)(lambda). The values of the lowest layer were compared to the in-situ values after conversion of the latter ones to ambient RH. The comparison showed a good correlation of R-2 = 0.62-0.78, but the extinction coefficients from MAX-DOAS were a factor of 1.5-3.4 larger than the insitu values. Best agreement is achieved for a few cases characterized by low aerosol optical depths and low planetary boundary layer heights. Differences were shown to be dependent on the applied MAX-DOAS retrieval algorithm. The comparison of the in-situ extinction data to a Raman LIDAR (light detection and ranging) showed a good correlation and higher values measured by the LIDAR (R-2 = 0.82-0.85, slope of 1.69-1.76) if the Raman retrieved profile was used to extrapolate the directly measured extinction coefficient to the ground. The comparison improved if only nighttime measurements were used in the comparison (R-2 = 0.96, slope of 1.12).

Keyword(s): J

Note: We thank Jacques Warmer and the staff of KNMI at the CESAR site for providing an excellent service during our campaign. We thank the CINDI local organization team at KNMI, in particular Ankie Piters, Mark Kroon, and Jennifer Hains, for facilitating this very successful campaign. We gratefully acknowledge Henk Klein-Baltink (KNMI) for providing the ceilometer data. We also gratefully acknowledge the easy access of the meteorological data used in this work via http://www.cesar-observatory.nl. We thank Rahel Fierz (PSI) for valuable discussions. Many thanks to Michel Tinquely (PSI) for helping out with the COSMO data, which was provided by the Swiss Federal Office of Meteorology and Climatology (MeteoSwiss). NILU and especially Ann Mari Fjaeraa are gratefully acknowledged for providing the air mass trajectories. Many thanks to A. Rozanov from the Institute of Environmental Physics, University of Bremen, for providing the SCIATRAN radiative transfer model to IUPHD. Hitoshi Irie thanks H. Takashima, Y. Kanaya, and PREDE, Co., Ltd for their technical assistance in developing and operating the MAX-DOAS instrument. Observation by JAMSTEC was supported by the Japan EOS Promotion Program of the Ministry of Education, Culture, Sports, Science and Technology (MEXT), and by the Global Environment Research Fund (S-7) of the Japanese Ministry of the Environment. Katrijn Clemer (BIRA-IASB) was financially supported by the AGACC project (contract SD/AT/10A) funded by the Belgian Federal Science Policy Office. This work was financially supported by the ESA Climate Change Initiative Aerosol_cci (ESRIN/Contract No. 4000101545/10/I-AM) and by the EC-projects Global Earth Observation and Monitoring (GEOmon, contract 036677) and European Supersites for Atmospheric Atmospheric Aerosol Research (EUSAAR, contract 026140).

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Contributing Institute(s):

1. Troposphäre (IEK-8)

Research Program(s):

1. Atmosphäre und Klima (P23)

Appears in the scientific report 2011

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