Radiative Effect of Springtime Biomass-Burning Aerosols over Northern Indochina during 7-SEAS/BASELInE 2013 Campaign

Abstract

The direct aerosol radiative effects of biomass-burning (BB) aerosols over northern Indochina were estimated by using aerosol properties (physical, chemical, and optical) along with the vertical profile measurements from ground-based measurements with integration of an optical and a radiative transfer model during the Seven South East Asian Studies/ Biomass-Burning Aerosols & Stratocumulus Environment: Lifecycles & Interactions Experiment (7-SEAS/BASELInE) conducted in spring 2013. Cluster analysis of backward trajectories showed the air masses arriving at mountainous background site (Doi Ang Khang; 19.93°N, 99.05°E, 1536 m above mean sea level) in northern Indochina, mainly from near-source inland BB activities and being confined in the planetary boundary layer. The PM 10 and black carbon (BC) mass were 87 ± 28 and 7 ± 2 µg m -3 , respectively. The aerosol optical depth (AOD 500 ) was found to be 0.26-1.13 (0.71 ± 0.24). Finer (fine mode fraction ≈0.95, angstrom-exponent at 440-870 nm ≈1.77) and significantly absorbing aerosols (singlescattering albedo ≈0.89, asymmetry-parameter ≈0.67, and absorption AOD ≈0.1 at 440 nm) dominated over this region. BB aerosols (water soluble and BC) were the main contributor to the aerosol radiative forcing (ARF), while others (water insoluble, sea salt and mineral dust) were negligible mainly due to their low extinction efficiency. BC contributed only 6% to the surface aerosol mass but its contribution to AOD was 12% (2 times higher). The overall mean ARF was -8.0 and -31.4 W m -2 at top-of-atmosphere (TOA) and at the surface (SFC), respectively. Likely, ARF due to BC was +10.7 and -18.1 W m -2 at TOA and SFC, respectively. BC imposed the heating rate of +1.4 K d -1 within the atmosphere and highlighting its pivotal role in modifying the radiation budget. We propose that to upgrade our knowledge on BB aerosol radiative effects in BB source region, the long-term and extensive field measurements are needed.

COVID-19's impact on the atmospheric environment in the Southeast Asia region

“…Over SEA, aerosols are mainly from urban and industrial emissions (organics, sulfate, nitrate, ammonium), black carbon from fossilfuel combustion and biofuel burning, volcanic ash, sea salts and dust transported by long distances, while during pre-monsoon extensive forest and vegetation fires occur (Chuersuwan et al, 2008;Hai and Kim Oanh, 2013;Tsai et al, 2013;Kanniah, 2014;Kanniah et al, 2016;Khan et al, 2016;Pani et al, 2018;Dahari et al, 2019). Therefore, aerosols are mixtures of various types creating hybrid particles and rendering their radiative effects highly uncertain (Pani et al, 2016). In addition, trace gases such as sulfur dioxide (SO 2 ), nitrogen oxides (NO x ), ammonia (NH 3 ) and carbon monoxide (CO) are precursors of inorganic (sulfate, nitrate, ammonium and their mixtures, NH 4 NO 3 , (NH 4 ) 2 SO 4 , NH 4 HSO 4 ) and organic aerosols after complex homogeneous or heterogeneous chemical reactions in the atmosphere (Pandolfi et al, 2012;Henschel et al, 2015;Kharol et al, 2018;EPA, 2020).…”

“…Assessing the total amount of columnar aerosol is critical not only for studying its impact on human health but also on solar radiation, cloud condensation processes, and climate change over South and Southeast Asia (e.g. Dumka et al, 2015;Pani et al, 2016Pani et al, , 2018Singh et al, 2020). Since the high pollution levels is a major environmental and health issue in SEA countries, it is essential to understand the degree and the spatial extent of the decrease in air pollutants and aerosols due to restriction measures during the COVID-19 period in spring 2020.…”

Satellite-Surface Perspectives of Air Quality and Aerosol-Cloud Effects on the Environment: An Overview of 7-SEAS/BASELInE

“…Extending from the optical closure modeling (Bell et al, 2013;Pani et al, 2016a) for regional biomass-burning aerosols, Pani et al (2016b) reported, for the first time, a detailed estimation of direct aerosol radiative effect (DARE) near source regions over northern SAP by using in-situ datasets (i.e., ground-based measurement of aerosol physical, chemical, and optical properties) and a radiative transfer model during the spring of 2013 BASELInE campaign. Their results provided strong evidence that biomass-burning aerosols (mainly water soluble and black carbon) enhance the surface cooling (as high as -33.5 W m -2 in 24-hour mean) as well as atmospheric warming (as high as +24.7 W m -2 ), which could significantly influence the diurnally-averaged radiative energetics.…”

Superposition of Gobi Dust and Southeast Asian Biomass Burning: The Effect of Multisource Long‐Range Transport on Aerosol Optical Properties and Regional Meteorology Modification

“…The heating rates due to black carbon were higher than those due to the total aerosols. In a case study of two‐layer heavy smoke long‐range transport, enhanced aerosol radiative efficiency at both surface and lower atmosphere were found with high atmospheric heating rate of 1.3 K/day ( Pani et al, ).…”