Mainz, Universiẗat, Diss., 2003. / Enth. 1 Sonderabdr. aus: Journal of geophysical research ; Vol. 107. 2002.

Heidelberg, Universiẗat, Diss., 2002.

Mainz, Universiẗat, Diss., 2002.

Mainz, Universiẗat, Diss., 2003. / Etnh. 5 Sonderabdr. aus verschiedenen Publikationen.

Giessen, Universiẗat, Diss., 2004.

München, Techn. Universiẗat, Diss., 2004.

The composition, concentration, and size of submicron aerosols were measured with a time resolution of five minutes by an Aerodyne high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS) at a rural location northwest of the Dallas-Fort Worth, TX, area for the month of June 2011. A TSI, Inc., Model AE51 aethalometer using an optical absorption technique also was deployed to measure black carbon (BC) concentrations. The total measured PM1 mass concentration ranged between 1.0 µg/m3 and 17.1 µg/m3, with a mean and standard deviation of 4.6± 2.7 µg/m3. Significant variability is observed in the time series of total PM1 and of all four HR-ToF-AMS species, particularly between June 21 and 25. The average aerosol composition was dominated by organic matter (52.1 ± 14.8%) and sulfate (28.8 ± 11.8%). Organic aerosol concentrations were positively correlated with tracers of combustion carbon monoxide (CO) and BC, the coefficients of determination were r2=064 and r2=0.48, respectively. Because of the large influence of organics on total aerosol concentration, organic data were analyzed in the context of ΔOA/ΔCO, which typically is used to investigate the relative importance of secondary organic aerosol. The average ∆OA/∆CO for the data used was 64.0 ± 26.9 µg/ (m3 ppmv), which is typical of an aged air mass. Other metrics of age include the ratio of OOAI (more oxidized) to total oxidized organic aerosol (OOA), the ratio of sulfate to total sulfur, the ratio of its oxidation products to isoprene, and the ratio of nitrogen oxides to total reactive nitrogen. All metrics point to aged air masses, but variations in these age matrices, particularly during one period of enhanced ΔOA/ΔCO, help elucidate the contributions of various precursors and processes to organic aerosols at the site.

The representation of aerosol processes and the skill in simulating the Asian summer monsoon vary widely across climate models. Yet, for the second half of the twentieth century, the models from the Coupled Model Intercomparison Project Phase 5 (CMIP5) show a robust decrease of average precipitation in the South and Southeast Asian (SSEA) continental region due to the increase of anthropogenic aerosols. When taking into account anthropogenic aerosols as well as greenhouse gases (GHGs), the 15 CMIP5 models considered in this study yield an average June–September precipitation least squares linear trend of −0.20 ± 0.20mm d−1 (50 years)−1, or −2.9%, for all land points in the SSEA region (taken from 75 to 120◦E and 5 to 30◦N) in the years from 1950 to 1999 (multimodel average ± one standard deviation) in spite of an increase in the water vapor path of +0.99 ± 0.65 kg m−2 (50 years)−1 (+2.5%). This negative precipitation trend differs markedly from the positive precipitation trend of +0.29 ± 0.14mm d−1 (50 years)−1, or +4.1%, which is computed for GHG forcing only. Taking into account aerosols both decreases the water vapor path and slows down the monsoon circulation as suggested by several previous studies. At smaller scales, however, internal variability makes attributing observed precipitation changes to anthropogenic aerosols more difficult. Over Northern Central India (NCI), the spread between precipitation trends from individual model realizations is generally comparable in magnitude to simulated changes due to aerosols, and the model results suggest that the observed drying in NCI might in part be explained by internal variability.

Spektralradiometermessungen (spektrale optische Dicke und Himmelshelligkeitsfunktion) unter Hochgebirgsbedingungen (Zugspitze, 2965 m) wurden zur Bestimmung der klirnarelevanten Aerosolparameter des stratosphärischen Vulkanaerosols (speziell des Pinatubo) verwendet. Die erhaltenen klirnarelevanten Aerosolparameter aus den Meßkampagnen werden mit Angaben der Aerosolklimatologien verglichen und zur Abschätzung des kurzwelligen Strahlungsforcings durch das Pinatubo-Aerosol verwendet. / Spectral radiometer measurements (spectral optical thickness and sky brightness function) under high mountain conditions (Zugspitze, 2965 m) have been used for the determination of climate-relevant aerosol parameters of the stratospheric volcanic aerosol (columnar size distribution, refractive index, phase function and asymmetry parameter - especially of the aerosol of the Pinatubo volcano eruption in 1991). The climate-relevant aerosol parameters of the measurement campaigns and their temporal change have been compared with data of the aerosol climatologies and have been used for the estimation of the short wave radiative forcing of the Pinatubo event.

The main uncertainty in anthropogenic forcing of the Earth’s climate stems from pollution aerosols, particularly their ‘‘indirect effect’’ whereby aerosols modify cloud properties. We develop a new methodology to derive a measurement-based estimate using almost exclusively information from an Earth radiation budget instrument (CERES) and a radiometer (MODIS). We derive a statistical relationship between planetary albedo and cloud properties, and, further, between the cloud properties and column aerosol concentration. Combining these relationships with a data set of satellite-derived anthropogenic aerosol fraction, we estimate an anthropogenic radiative forcing of -0.9 ± 0.4 Wm-2 for the aerosol direct effect and of -0.2 ± 0.1 Wm-2 for the cloud albedo effect. Because of uncertainties in both satellite data and the method, the uncertainty of this result is likely larger than the values given here which correspond only to the quantifiable error estimates. The results nevertheless indicate that current global climate models may overestimate the cloud albedo effect.