Abstract
Black carbon (BC) is an essential climate forcer in the atmosphere. Large uncertainties remain in BC’s radiative forcing estimation by models, partially due to the limited measurements of BC vertical distributions near the surface layer. We conducted time-resolved vertical profiling of BC using a 356-m meteorological tower in Shenzhen, China. Five micro-aethalometers were deployed at different heights (2, 50, 100, 200, and 350 m) to explore the temporal dynamics of BC vertical profile in the highly urbanized areas. During the observation period (December 6–15, 2017), the average equivalent BC (eBC) concentrations were 6.6 ± 3.6, 5.4 ± 3.3, 5.9 ± 2.8, 5.2 ± 1.8, and 4.9 ± 1.4 μg m−3, from 2 to 350 m, respectively. eBC temporal variations at different heights were well correlated. eBC concentrations generally decreased with height. At all five heights, eBC diurnal variations exhibited a bimodal pattern, with peaks appearing at 09:00–10:00 and 19:00–21:00. The magnitudes of these diurnal peaks decreased with height, and the decrease was more pronounced for the evening peak. eBC episodes were largely initiated by low wind speeds, implying that wind speed played a key role in the observed eBC concentrations. eBC wind-rose analysis suggested that elevated eBC events at different heights originate from different directions, which suggested contributions from local primary emission plumes. Air masses from central China exhibited much higher eBC levels than the other three backward trajectory clusters found herein. The absorption Ångström exponent (AAE375–880) showed clear diurnal variations at 350 m and increased slightly with height.
Highlights
Black carbon (BC) is an important atmospheric aerosol component and is produced by the incomplete combustion of Electronic supplementary material The online version of this article contains supplementary material, which is available to authorized users.carbonaceous materials (Bond and Bergstrom 2006)
The results suggest that high equivalent BC (eBC) concentrations come from different directions at different heights
EBC variations were measured at five altitudes (2, 50, 100, 200, and 350 m) using the 356-m Shenzhen meteorological tower (SZMT)
Summary
BC aerosol can affect the climate by modifying the radiative properties of the atmosphere (Reddy and Boucher 2007). BC may be the third most important component of global warming after CO2 and CH4 (Bond et al 2013). Because BC can have substantial impacts on global climate change, regional ambient air quality, and human health, BC has become an increasingly important field of atmospheric research in recent years (Bond et al 2013). Modeling studies suggested that substantial uncertainties of BC radiative forcing were arise from limited measurement of BC vertical profiles (Samset et al 2013; Zarzycki and Bond 2010). Field measurements of BC vertical profiles are useful for reducing the uncertainties of BC radiative forcing in climate models
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