Direct measurements of black carbon fluxes in central Beijing using the eddy covariance method

Joshi, Rutambhara and Liu, D. and Nemitz, E. and Langford, B. and Mullinger, N. and Squires, F. and Lee, J. and Wu, Y. and Pan, Xiaole and Fu, Pingqing and Kotthaus, S. and Grimmond, S. and Zhang, Q. and Wu, Ruili and Wild, O. and Flynn, Michael and Coe, Hugh and Allan, James (2021) Direct measurements of black carbon fluxes in central Beijing using the eddy covariance method. Atmospheric Chemistry and Physics, 21 (1). pp. 147-162. ISSN 1680-7324

Abstract

Black carbon (BC) forms an important component of particulate matter globally, due to its impact on climate, the environment and human health. Identifying and quantifying its emission sources are critical for effective policymaking and achieving the desired reduction in air pollution. In this study, we present the first direct measurements of urban BC fluxes using eddy covariance. The measurements were made over Beijing within the UK-China Air Pollution and Human Health (APHH) winter 2016 and summer 2017 campaigns. In both seasons, the mean measured BC mass (winter: 5.49 ng m−2 s−1, summer: 6.10 ng m−2 s−1) and number fluxes (winter: 261.25 particles cm−2 s−1, summer: 334.37 particles cm−2 s−1) were similar. Traffic was determined to be the dominant source of the BC fluxes measured during both seasons. The total BC emissions within the 2013 Multi-resolution Emission Inventory for China (MEIC) are on average too high compared to measured fluxes by a factor of 58.8 (winter) and 47.2 (summer). Only a comparison with the MEIC transport sector shows that emissions are also larger (factor of 37.5 in winter and 37.7 in summer) than the measured flux. Emission ratios of BC ∕ NOx and BC ∕ CO are comparable to vehicular emission control standards implemented in January 2017 for gasoline (China 5) and diesel (China V) engines, indicating a reduction of BC emissions within central Beijing, and extending this to a larger area would further reduce total BC concentrations.