Khanneh Wadinga Fomba

Enhanced Role of Transition Metal Ion Catalysis During In-Cloud Oxidation of SO2

Dust in the Clouds Sulfate aerosols have the greatest radiative impact on climate systems. Harris et al. (p. 727) report that the oxidation of sulfur dioxide gas, catalyzed by natural transition metal ions mostly on the surface of coarse mineral dust, is the dominant pathway for sulfate production in clouds. In view of the growing sulfur dioxide emissions from large, industrializing countries, including this process in climate models should improve the agreement between models and observations. Transition metal ions catalyze most of the oxidation of sulfur dioxide that occurs in clouds. Global sulfate production plays a key role in aerosol radiative forcing; more than half of this production occurs in clouds. We found that sulfur dioxide oxidation catalyzed by natural transition metal ions is the dominant in-cloud oxidation pathway. The pathway was observed to occur primarily on coarse mineral dust, so the sulfate produced will have a short lifetime and little direct or indirect climatic effect. Taking this into account will lead to large changes in estimates of the magnitude and spatial distribution of aerosol forcing. Therefore, this oxidation pathway—which is currently included in only one of the 12 major global climate models—will have a significant impact on assessments of current and future climate.

Size distribution and source of heavy metals in particulate matter on the lead and zinc smelting affected area

In order to understand the size distribution and the main kind of heavy metals in particulate matter on the lead and zinc smelting affected area, particulate matter (PM) and the source samples were collected in Zhuzhou, Hunan Province from December 2011 to January 2012 and the results were discussed and interpreted. Atmospheric particles were collected with different sizes by a cascade impactor. The concentrations of heavy metals in atmospheric particles of different sizes, collected from the air and from factories, were measured using an inductively coupled plasma mass spectrometry (ICP-MS). The results indicated that the average concentration of PM, chromium (Cr), arsenic (As), cadmium (Cd) and lead (Pb) in PM was 177.3 ± 33.2 μg/m3, 37.3 ± 8.8 ng/m3, 17.3 ± 8.1 ng/m3, 4.8 ± 3.1 ng/m3 and 141.6 ± 49.1 ng/m3, respectively. The size distribution of PM displayed a bimodal distribution; the maximum PM size distribution was at 1.1-2.1 μm, followed by 9-10 μm. The size distribution of As, Cd and Pb in PM was similar to the distribution of the PM mass, with peaks observed at the range of 1.1-2.1 μm and 9-10 μm ranges while for Cr, only a single-mode at 4.7-5.8 μm was observed. PM (64.7%), As (72.5%), Cd (72.2%) and Pb (75.8%) were associated with the fine mode below 2.1 μm, respectively, while Cr (46.6%) was associated with the coarse mode. The size distribution characteristics, enrichment factor, correlation coefficient values, source information and the analysis of source samples showed that As, Cd and Pb in PM were the typical heavy metal in lead and zinc smelting affected areas, which originated mainly from lead and zinc smelting sources.

Central Asian Dust Experiment (CADEX): First Year Lidar Observations

Dust influences climate and weather by direct and indirect radiative effects or heterogeneous ice nucleation. Dust is often transported to and across Tajikistan. Tajikistan and Central Asia suffer from climate change and the potential role of dust needs to be investigated. But up to now, only a small number of measurements are available in that region, especially no vertical profiles of aerosol optical properties are known. Therefore the Central Asian Dust EXperiment (CADEX) conducts first lidar measurements in Tajikistan for long-term vertically resolved aerosol measurements from March 2015–September 2016. The multiwavelength polarization Raman lidar PollyXT is used for these measurements. Two characteristic measurement examples of dust layers are presented in this contribution.

Central Asian Dust Experiment (CADEX) and Comparison of Lidar Ratios of Asian and Saharan Dust

We report about first aerosol lidar measurements that were performed in Dushanbe, Tajikistan (Central Asia) during our Central Asian Dust EXperiment (CADEX) project. The determined intensive property depolarization ratio allows an aerosol characterization and often shows mineral dust at lofted layers during spring time and optically and geometrically thick layers that touch the surface during summer time. The intensive property lidar ratio shows lower values for Asian dust than the lidar ratios measured from Saharan dust during our former campaigns in Morocco and Cape Verde. We show one measurement example from CADEX, allocate the possible dust source area for this measurement and discuss the measured differences between Asian and Saharan dust.