Spatial and temporal variations of gaseous and particulate pollutants in six sites in Tibet, China, during 2016–2017

Abstract

Long-term air quality data with high temporal and spatial resolutions are necessary to understand some processes influencing air quality and corresponding environmental and health effects. In this study, spatiotemporal variations of PM 2.5 , PM 10 , SO 2 , NO 2 , CO, and O 3 were investigated over a one-year period (June 2016–May 2017) at six sites of the Tibetan Plateau (TP). The annual mean concentrations of PM 2.5 in all cities except Nagchu were below the Grade II standard (35 µg m –3 ), and the values in Nagri and Nyingchi were even less than the Grade I standard (15 µg m –3 ). PM 10 concentrations showed similar distribution pattern with PM 2.5 . Evident seasonal variations of PM 2.5 , PM 10 , SO 2 , NO 2 , and CO concentrations were observed, with the highest seasonal average value being in winter followed by fall, spring, and summer, in descending order. By contrast, the 8-h O 3 concentration showed an opposite seasonal variation because the O 3 depended on lots of factors such as stratospheric incursions, weather conditions, and intensity of solar radiation. The diurnal trends of PM 2.5 , PM 10 , SO 2 , NO 2 , and CO concentrations in study region generally showed a flat “W” shape with two peaks occurring around noon (10:00–12:00) and midnight (21:00–23:00); these peaks were found to be affected by emission sources and weather conditions. However, the O 3 concentration trends did not significantly differ among the six regions, with the maximum concentration being in the afternoon. In sum, cities on the TP showed slightly higher pollution levels in regions affected by anthropogenic activities such as Lhasa and Nagchu, whereas other cities showed good air quality. Beside long-range transport pollutants from surrounding regions, local emissions (e.g., biomass burning, religious activities) also contributed much to the atmospheric pollutants. This study provides a basis for the formulation of future urban air pollution control measures on the TP.