Effects of transport on a biomass burning plume from Indochina during EMeRGe-Asia identified by WRF-Chem
Authors: Lin Chuan-Yao , Chen Wan-Chin , Chien Yi-Yun , Chou Charles C. K. , Liu Chian-Yi , Ziereis Helmut , Schlager Hans , Förster Eric , Obersteiner Florian , Krüger Ovid O. , Holanda Bruna A. , Pöhlker Mira L. , Kaiser Katharina , Schneider Johannes , Bohn Birger , Pfeilsticker Klaus , Weyland Benjamin , Andrés Hernández Maria Dolores , Burrows John P. 
Published: February 2023

Abstract. The Indochina biomass burning (BB) season in springtime has a substantial
environmental impact on the surrounding areas in Asia. In this study, we
evaluated the environmental impact of a major long-range BB transport event
on 19 March 2018 (a flight of the High Altitude and Long Range Research Aircraft (HALO; https://www.halo-spp.de, last access: 14 February 2023) research aircraft, flight F0319)
preceded by a minor event on 17 March 2018 (flight F0317). Aircraft data
obtained during the campaign in Asia of the Effect of Megacities on the
transport and transformation of pollutants on the Regional to Global scales
(EMeRGe) were available between 12 March and 7 April 2018. In F0319,
results of 1 min mean carbon monoxide (CO), ozone (O3), acetone (ACE),
acetonitrile (ACN), organic aerosol (OA), and black carbon aerosol (BC)
concentrations were up to 312.0, 79.0, 3.0, and 0.6 ppb and 6.4 and 2.5 µg m−3, respectively, during the flight, which
passed through the BB plume transport layer (BPTL) between the elevation of
2000–4000 m over the East China Sea (ECS). During F0319, the CO, O3, ACE,
ACN, OA, and BC maximum of the 1 min average concentrations were higher in
the BPTL by 109.0, 8.0, 1.0, and 0.3 ppb and 3.0 and
1.3 µg m−3 compared to flight F0317, respectively. Sulfate
aerosol, rather than OA, showed the highest concentration at low altitudes
(<1000 m) in both flights F0317 and F0319 resulting from the
continental outflow in the ECS. The transport of BB aerosols from Indochina and its impacts on the
downstream area were evaluated using a Weather Research Forecasting with Chemistry (WRF-Chem) model. The modeling results
tended to overestimate the concentration of the species, with examples being
CO (64 ppb), OA (0.3 µg m−3), BC (0.2 µg m−3), and O3
(12.5 ppb) in the BPTL. Over the ECS, the simulated BB contribution
demonstrated an increasing trend from the lowest values on 17 March 2018 to
the highest values on 18 and 19 March 2018 for CO, fine particulate matter
(PM2.5), OA, BC, hydroxyl radicals (OH), nitrogen oxides (NOx),
total reactive nitrogen (NOy), and O3; by contrast, the variation
of J(O1D) decreased as the BB plume's contribution increased over the
ECS. In the lower boundary layer (<1000 m), the BB plume's
contribution to most species in the remote downstream areas was <20 %. However, at the BPTL, the contribution of the long-range transported
BB plume was as high as 30 %–80 % for most of the species (NOy,
NOx, PM2.5, BC, OH, O3, and CO) over southern China (SC),
Taiwan, and the ECS. BB aerosols were identified as a potential source of
cloud condensation nuclei, and the simulation results indicated that the
transported BB plume had an effect on cloud water formation over SC and the
ECS on 19 March 2018. The combination of BB aerosol enhancement with cloud
water resulted in a reduction of incoming shortwave radiation at the surface
in SC and the ECS by 5 %–7 % and 2 %–4 %, respectively, which potentially
has significant regional climate implications.