Abstract
Black carbon (BC) aerosol plays an important role in climate forcing. The net radiative effect is strongly dependent on the physical properties of BC particles. A single particle soot photometer and a carbon monoxide analyser were deployed during the Chinese Lunar Year (CLY) and on weekdays at Xi’an, China, to investigate the characteristics of refractory black carbon aerosol (rBC). The rBC mass on weekdays (8.4 μg·m−3) exceeds that during the CLY (1.9 μg·m−3), presumably due to the lower anthropogenic emissions during the latter. The mass size distribution of rBC shows a primary mode peak at ~205 nm and a small secondary mode peak at ~102-nm volume-equivalent diameter assuming 2 g·cm−3 in void-free density in both sets of samples. More than half of the rBC cores are thickly coated during the CLY (fBC = 57.5%); the percentage is slightly lower (fBC = 48.3%) on weekdays. Diurnal patterns in rBC mass and mixing state differ for the two sampling periods, which are attributed to the distinct anthropogenic activities. The rBC mass and CO mixing ratios are strongly correlated with slopes of 0.0070 and 0.0016 μg·m−3·ppbv−1 for weekdays and the CLY, respectively.
Highlights
Black carbon (BC) aerosol, a by-product of the incomplete combustion of fossil fuels and biomass, plays a unique and important role in Earth’s climate system
Anthropogenic emissions are reduced during these events in Shanghai and Beijing, because the government implements a series of air pollution control measures to improve the air quality; these include reducing emissions from coal-fired power plants and strict regulations on motor vehicle usage
Comparisons were made between samples collected during the Chinese Lunar Year (CLY), when anthropogenic emissions were reduced, and samples collected on normal weekdays
Summary
Black carbon (BC) aerosol, a by-product of the incomplete combustion of fossil fuels and biomass, plays a unique and important role in Earth’s climate system. Most studies (e.g., [12,13]) in China have used filter-based techniques that measure bulk aerosol absorption rather than the BC mass concentrations directly. Previous studies indicate that key properties of the BC aerosol, that is the particle’s concentration, size, shape and mixing state, vary in complex ways and that these properties depend on many interacting environmental factors [14,15]. We report the results of a study on individual refractory black carbon (rBC) mass concentrations, size distributions, the mixing state and the relationship with carbon monoxide (CO). 2.5 micrometres) during this period (128.9 μg·m−3) is much lower than on weekdays (191.4 μg·m−3) This gives researchers a once-a-year opportunity to study the atmosphere when anthropogenic emissions are greatly reduced.
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