Abstract
The spring 2015 deployment of a suite of instrumentation at Doi Ang Khang (DAK) in northwestern Thailand enabled the characterization of air masses containing smoke aerosols from burning predominantly in Myanmar. Aerosol Robotic Network (AERONET) Sun photometer data were used to validate Moderate Resolution Imaging Spectroradiometer (MODIS) Collection 6 ‘Deep Blue’ aerosol optical depth (AOD) retrievals; MODIS Terra and Aqua provided results of similar quality, with correlation coefficients of 0.93–0.94 and similar agreement within expected uncertainties to global-average performance. Scattering and absorption measurements were used to compare surface and total column aerosol single scatter albedo (SSA); while the two were well-correlated, and showed consistent positive relationships with moisture (increasing SSA through the season as surface relative humidity and total columnar water vapor increased), in-situ surface-level SSA was nevertheless significantly lower by 0.12–0.17. This could be related to vertical heterogeneity and/or instrumental issues. DAK is at ~1,500 m above sea level in heterogeneous terrain, and the resulting strong diurnal variability in planetary boundary layer depth above the site leads to high temporal variability in both surface and column measurements, and acts as a controlling factor to the ratio between surface particulate matter (PM) levels and column AOD. In contrast, while some hygroscopic effects were observed relating to aerosol particle size and Ångström exponent, relative humidity variations appear to be less important for the PM:AOD ratio here.
Highlights
As part of the Seven South-East Asian Studies (7-SEAS) project (Lin et al, 2013; Reid et al, 2013), the Biomassburning Aerosols & Stratocumulus Environment: Lifecycles and Interactions Experiment (BASELInE, Tsay et al, 2013; 2016) was intended to probe physicochemical processes, interactions, and feedbacks related to biomass burning aerosols and clouds during the spring burning season (February–April) in southeast Asia (SEA)
This study presents first results from in-situ aerosol observations made by the COMMIT mobile laboratory at the 2015 Doi Ang Khang (DAK) deployment, together with remotely-sensed aerosol information from the Aerosol Robotic Network (AERONET) Sun photometer and Moderate Resolution Imaging Spectroradiometer (MODIS) data products
Similar albeit weaker correlations are found between insitu surface single scatter albedo (SSA) and surface relative humidity (RH) measured at DAK (R = 0.69 and 0.68 for AETH, 0.65 and 0.49 for Particle Soot/Absorption Photometer (PSAP), at 440 and 675 nm respectively; note these correlations represent all available in situ SSA data, not the small subset where there is a temporal match with AERONET in Fig. 8), suggesting that some of the variability in both surface and column SSA is driven by variability in moisture, and that this is reflected in moisture within the smoke plume as well as the total column
Summary
As part of the Seven South-East Asian Studies (7-SEAS) project (Lin et al, 2013; Reid et al, 2013), the Biomassburning Aerosols & Stratocumulus Environment: Lifecycles and Interactions Experiment (BASELInE, Tsay et al, 2013; 2016) was intended to probe physicochemical processes, interactions, and feedbacks related to biomass burning aerosols and clouds during the spring burning season (February–April) in southeast Asia (SEA). The surface-level relative humidity (not shown) varied generally in the range 20–40% from the start of the deployment until DOY 81 (March 22); from until DOY 89, which coincides with the period of decreased aerosol loading in all the satellite and in-situ data, RH varied between 40–90% (note the RH monitor deployed at DAK caps at 90%).
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