Journal Article
Atmospheric Chemistry and Physics, vol. 18, iss. 2, pp. 1395-1417, 2018
Authors
Tianyi Fan, Xiaohong Liu, Po-Lun Ma, Qiang Zhang, Zhanqing Li, Yiquan Jiang, Fang Zhang, Chuanfeng Zhao, Xin Yang, Fang Wu, Yuying Wang
Abstract
Abstract. Global climate models often underestimate aerosol loadings in China, and
these biases can have significant implications for anthropogenic aerosol
radiative forcing and climate effects. The biases may be caused by either the
emission inventory or the treatment of aerosol processes in the models, or
both, but so far no consensus has been reached. In this study, a relatively
new emission inventory based on energy statistics and technology,
Multi-resolution Emission Inventory for China (MEIC), is used to drive the
Community Atmosphere Model version 5 (CAM5) to evaluate aerosol distribution
and radiative effects against observations in China. The model results are
compared with the model simulations with the widely used Intergovernmental
Panel on Climate Change Fifth Assessment Report (IPCC AR5) emission
inventory. We find that the new MEIC emission improves the aerosol optical
depth (AOD) simulations in eastern China and explains 22–28 % of the AOD
low bias simulated with the AR5 emission. However, AOD is still biased low in
eastern China. Seasonal variation of the MEIC emission leads to a better
agreement with the observed seasonal variation of primary aerosols than the
AR5 emission, but the concentrations are still underestimated. This implies
that the atmospheric loadings of primary aerosols are closely related to the
emission, which may still be underestimated over eastern China. In contrast,
the seasonal variations of secondary aerosols depend more on aerosol
processes (e.g., gas- and aqueous-phase production from precursor gases) that
are associated with meteorological conditions and to a lesser extent on the
emission. It indicates that the emissions of precursor gases for the
secondary aerosols alone cannot explain the low bias in the model.
Aerosol secondary production processes in CAM5
should also be revisited. The simulation using MEIC estimates the
annual-average aerosol direct radiative effects (ADREs) at the top of the
atmosphere (TOA), at the surface, and in the atmosphere to be −5.02,
−18.47, and 13.45 W m−2, respectively, over eastern China, which are
enhanced by −0.91, −3.48, and 2.57 W m−2 compared with the AR5
emission. The differences of ADREs by using MEIC and AR5 emissions are larger
than the decadal changes of the modeled ADREs, indicating the uncertainty of
the emission inventories. This study highlights the importance of improving
both the emission and aerosol secondary production processes in modeling the
atmospheric aerosols and their radiative effects. Yet, if the estimations of
MEIC emissions in trace gases do not suffer similar biases to those in the
AOD, our findings will help affirm a fundamental error in the conversion from
precursor gases to secondary aerosols as hinted in other recent studies
following different approaches.
