Effect of meteorological conditions on PM.sub.10 concentrations in the middle reaches of the Yarlung Zangbo River, Tibet Plateau

Concentrations of airborne particulate matter with a diameter [less than or equal to] 10 [micro]m (PM.sub.10) 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 PM.sub.10 emission. To provide more information, we used a laser particle counter to measure PM.sub.10 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 PM.sub.10 concentration and the effect of meteorological conditions on emission and transport. The daily mean PM.sub.10 concentration ranged from 26.9 to 253.3 [micro]g m.sup.-3 for a mean wind velocity ranging from 2.1 to 9.7 m s.sup.-1, and a maximum wind velocity ranging from 4.6 to 14.7 m s.sup.-1. Mean hourly PM.sub.10 can reach 800 [micro]g m.sup.-3, and hourly wind velocity, air temperature, relative humidity, and soil temperature all affect PM.sub.10, but their effects vary spatially. The hourly mean PM.sub.10 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 PM.sub.10 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.