Vertical Distribution and Columnar Optical Properties of Springtime Biomass-Burning Aerosols over Northern Indochina during 2014 7-SEAS Campaign

Abstract

In this study, the aerosol optical properties and vertical distributions in major biomass-burning emission area of northern Indochina were investigated using ground-based remote sensing (i.e., four Sun-sky radiometers and one lidar) during the Seven South East Asian Studies/Biomass-burning Aerosols & Stratocumulus Environment: Lifecycles & Interactions Experiment conducted during spring 2014. Despite the high spatial variability of the aerosol optical depth (AOD; which at 500 nm ranged from 0.75 to 1.37 depending on the site), the temporal variation of the daily AOD demonstrated a consistent pattern among the observed sites, suggesting the presence of widespread smoke haze over the region. Smoke particles were characterized as small (Ångström exponent at 440-870 nm of 1.72 and fine mode fraction of 0.96), strongly absorbing (single-scattering albedo at 440 nm of 0.88), mixture of black and brown carbon particles (absorption Ångström exponent at 440-870 nm of 1.5) suspended within the planetary boundary layer (PBL). Smoke plumes driven by the PBL dynamics in the mountainous region reached as high as 5 km above sea level; these plumes subsequently spread out by westerly winds over northern Vietnam, southern China, and the neighboring South China Sea. Moreover, the analysis of diurnal variability of aerosol loading and optical properties as well as vertical profile in relation to PBL development, fire intensity, and aerosol mixing showed that various sites exhibited different variability based on meteorological conditions, fuel type, site elevation, and proximity to biomass-burning sources. These local factors influence the aerosol characteristics in the region and distinguish northern Indochina smoke from other biomass-burning regions in the world.

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

“…Compared with results from Sayer et al (2014) and Wang et al (2015), higher values and similar trend in AE 440/870 was seen for BB aerosols over Amazon (≈1.9-2.0) basin, Savanna (≈1.9-2.0) forest, and Australia (≈1.9) followed by Indochina (≈1.7-1.8) and Boreal forests (≈1.4-1.7) of North America and Russia. The SSA440 (as shown in Table 2) Table 2, we can conclude that the optical properties of BB aerosols over northern Indochina are distinct from those over other BB regions by taking everything into account.…”

“…4(d)) varied in between 0.85-0.94 (with a mean 0.89 ± 0.02) over DAK and suggested the dominance of BB aerosols. Wang et al (2015) reported the presence of strongly absorbing (SSA 440 ≈0.88) smoke particles over northern Indochina in 2014 spring. It was also observed that SSA decreases with wavelength (SSA 440 ≈0.89) and SSA 1020 ≈0.84).…”

“…Moreover, some recent studies also emphasized the BB emissions from Indochina region and explained their impact on regional air quality, atmospheric radiation, hydrological cycle, and climate (e.g., Lin et al, 2013;Tsay et al, 2013;Lin et al, 2014;Tsay et al, 2016) by using in-situ measurements (e.g., Chuang et al, 2013b;Wang et al, 2015;Chuang et al, 2016;Hsiao et al, 2016;Khamkaew et al, 2016;Pantina et al, 2016;Sayer et al, 2016), satellite observations (e.g., Hsu et al, 2003;Huang et al, 2011;Campbell et al, 2013;Lee et al, 2016b), remote sensing Reid et al, 2013), and modeling studies (Fu et al, 2012;Loftus et al, 2016) within the 7-SEAS framework. Wang et al (2015) investigated the presence of strongly absorbing (single-scattering albedo ≈0.88 and absorption angstrom exponent ≈1.5) carbonaceous aerosols within the planetary boundary layer (PBL) over northern Indochina in 2014 spring.…”

Characterization of Particulate Matter Profiling and Alveolar Deposition from Biomass Burning in Northern Thailand: The 7-SEAS Study

“…BC is responsible for the importance of BB-derived PM as it can effectively absorb light across the entire solar spectrum and contributes to the warming effect on the radiative budget of the earth (Jacobson, 2001;Wang et al, 2015;Sayer et al, 2016;Pani et al, 2016). Also, BC could play an important role in inhalation toxicity too (Cai et al, 2014).…”

Evaluation of Atmospheric PCDD/Fs at Two High-Altitude Stations in Vietnam and Taiwan during Southeast Asia Biomass Burning

“…Until then, measurements of PCDD/F concentrations in ambient air from this area were very limited or incomplete. Due to climatological wind trajectory direction at high altitudes, long-range regional transports of PCDD/Fs (and other pollutants) via the southwest monsoon can be clearly observed Wang et al, 2015). During the campaign, using data collected at the two high-altitude stations (Fig.…”