Sources, determination, monitoring, and transport of carbonaceous aerosols in Mainz, Germany

Abstract

Total atmospheric particulate matter, total carbon (TC), and black carbon (BC) were measured over two periods, spring and summer 1994, at a sampling location in Mainz, Germany. An optical (aethalometer) and a thermal method were used to determine BC since previous studies have shown that the optical method is dependent on the source of aerosols. The thermal method chosen for calibration enables the determination of molar hydrogen to carbon ratios for total particulate carbon and BC if quartz fiber filters were pre-treated at 850°C for 4 h. A specific attenuation cross-section of ≈7 m 2 g -1 for BC on the aethalometer filter was calculated which lies between values determined for cities and remote areas. Average concentrations of total particulate matter, TC, and BC were 38±17, 8.0±3.6, and 2.8±1.2 μg m -3, respectively. The paths and thus the source regions of the air masses were obtained by three-day back-trajectories calculated daily using actual meteorological data. Linear relationships were found for BC to TC and to the total aerosol mass indicating a common source, most likely fossil fuel combustion. Despite the linear relationship between BC and TC, a correlation between the variability of the BC/TC ratio and the paths of the air masses was seen. Since organic carbon and BC do influence the solar radiation budget and perhaps atmospheric chemistry, the ratio of BC to TC may serve as a good indicator for the assessment of the impact of carbonaceous aerosols. To better assess the global climatic impact of the carbonaceous component of aerosols, long-term measurements are certainly needed with a sufficient geographical coverage. Measurements of a single component such as BC with an aethalometer, for example, will not represent the whole impact that atmospheric particulate carbon can have on the solar radiation budget and atmospheric chemistry.