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Effect of Large-scale Biomass Burning on Aerosol Optical Properties at the GAW Regional Station Pha Din, Vietnam

Category: Optical/Radiative Properties and Remote Sensing

Volume: 19 | Issue: 5 | Pages: 1172-1187
DOI: 10.4209/aaqr.2018.11.0406
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Nicolas Bukowiecki 1, Martin Steinbacher2, Stephan Henne2, Nhat Anh Nguyen3, Xuan Anh Nguyen4, Anh Le Hoang5, Dac Loc Nguyen4, Hoang Long Duong3, Guenter Engling6, G√ľnther Wehrle1, Martin Gysel-Beer1, Urs Baltensperger 1

  • 1 Laboratory of Atmospheric Chemistry, Paul Scherrer Institute, 5232 Villigen PSI, Switzerland
  • 2 Laboratory for Air Pollution/Environmental Technology, Swiss Federal Laboratories for Materials Science and Technology (Empa), 8600 Dübendorf, Switzerland
  • 3 Hydro-Meteorological Observation Center (HYMOC), Vietnam Meteorological and Hydrological Administration (VNMHA), Ministry of Natural Resources and Environment (MONRE), Ha Noi, Vietnam
  • 4 Institute of Geophysics, Vietnam Academy of Science and Technology, Ha Noi, Vietnam
  • 5 Faculty of Environmental Sciences, VNU University of Science, Vietnam National University, Ha Noi, Vietnam
  • 6 Department of Biomedical Engineering and Environmental Sciences, National Tsing Hua University, Hsinchu 30013, Taiwan

Highlights

  • Continuous aerosol in-situ monitoring at a remote site in Northern SE Asia.
  • Biomass burning is identified using aethalometer measurements.
  • Peak influence from biomass burning in March and April.
  • Decreasing biomass burning peak intensities in the last five years measured at this site.
  • In-situ measurements during peak biomass influence are comparable to column measurements.

Abstract

In 2014, Pha Din (1466 m a.s.l.) was established as a Global Atmosphere Watch (GAW) regional station for aerosol and trace gas measurements in northwestern Vietnam. This study presents a five-year climatology of aerosol optical properties derived from nephelometer and aethalometer measurements and a comparison with ground-based remote sensing measurements at the nearby AERONET station Son La. The annual variations of the aerosol measurements at Pha Din are clearly dominated by annually recurring periods with high biomass burning activity in northern Southeast Asia (February–May). During these periods, the majority of air masses arriving at Pha Din originate from the southwest (northern Thailand, Laos and Myanmar). Both the meteorological conditions and the aerosol optical properties are very similar during the individual high biomass burning periods (increased temperature: > 20°C; moderate ambient relative humidity: 60–70%; decreased single scattering albedo: 0.8–0.9; increased absorption Ångström exponent: 1.6–2.0; and scattering Ångström exponent significantly larger than 1). Prior to the biomass burning season (October–January), the meteorological conditions at Pha Din are influenced by the SE Asian monsoon, leading to a frequent transport of air masses from SW China with moderate aerosol loadings. The lowest pollution levels are observed from June to September, which represents the wet season.

Keywords

Aerosol optical properties Biomass burning Black carbon Long-term measurements Global Atmosphere Watch


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