Effect of meteorological conditions on PM₁₀ concentrations in the middle reaches of the Yarlung Zangbo River, Tibet Plateau

Abstract

Concentrations of airborne particulate matter with a diameter ≤ 10 µm (PM₁₀) strongly affect local, regional, and global environments, human activities, and human health. The Yarlung Zangbo River in the southern Tibet Plateau creates a serious dust hazard, but there are few detailed field measurements of this region’s PM₁₀ emission. To provide more information, we used a laser particle counter to measure PM₁₀ concentrations above grassland floodplains, floodplains with a physical crust, shifting dunes, and shifting sand stabilized by planted trees. We used data from 9 days with a strong dust storm (between February and May 2021) to quantify spatial and temporal differences of PM₁₀ concentration and the effect of meteorological conditions on emission and transport. The daily mean PM₁₀ concentration ranged from 26.9 to 253.3 µg m⁻³ for a mean wind velocity ranging from 2.1 to 9.7 m s⁻¹, and a maximum wind velocity ranging from 4.6 to 14.7 m s⁻¹. Mean hourly PM₁₀ can reach 800 µg m⁻³, and hourly wind velocity, air temperature, relative humidity, and soil temperature all affect PM₁₀, but their effects vary spatially. The hourly mean PM₁₀ concentration increased with increasing mean hourly wind velocity above the shifting sand surface, but we found no significant relationships at the floodplain sites. The hourly mean PM₁₀ reached its maximum at a relative humidity of about 30%, with air temperature and soil temperature about 8 °C. Therefore, forecasting dust storms in the Yarlung Zangbo River basin will require knowledge of the land surface characteristics and the critical values of relative humidity and of air and soil temperatures.