Impact of Southeast Asian smoke on aerosol properties in Southwest China: First comparison of model simulations with satellite and ground observations

Smoke aerosols have been observed in Southwest China as a result of long-range transport

from surrounding areas in March and April. The processes driving this transport and the resultant impact

on regional aerosol optical properties are studied here through a combined use of the Goddard Earth

Observing System (GEOS)-Chem chemistry transport model in conjunction with satellite and the first-ever

ground-based observations in the Southwest China. The potential biomass burning source regions as well

as their respective contributions to aerosol loading in Southwest China are quantified. Compared to Sun

photometer observations of aerosol optical depth (AOD) at 550nm at eight stations in the study region

(10–28°N, 90–115°E, comprising Northeast India, Indo-China Peninsula, and Southwest and South China), the

AOD simulated by GEOS-Chem (nested grid with 0.5° × 0.667° resolution) by using the Fire Inventory from

National Center for Atmospheric Research shows an average bias of 0.17 during January 2012 to May 2013.

However, during the biomass burning months (March–April), the simulated AOD is much improved with a

bias of 0.04. Model sensitivity experiments show that biomass burning in Burma and Northeast India is the

largest contributor to smoke AOD (~88%) and total AOD (~57%) over Kunming, an urban site in Southwest

China. Case studies on 21–23 March 2013 show that the smoke layer in Northeast India and North Burma

can extend from the surface to 4 km and then be transported to Southwest China by prevailing westerly

airflow. Model-simulated AOD and vertical distribution of aerosols are respectively in good agreement with

satellite measurements from Moderate Resolution Imaging Spectroradiometer and Cloud-Aerosol Lidar with

Orthogonal Polarization.