Heavy near-surface PM_2.5 pollution in Lhasa, China during a relatively static winter period

Fairly high near-surface PM_2.5 concentrations were found during relatively static winter conditions within Lhasa - a Tibetan Plateau city normally considered to have a clean atmosphere. The average daily PM_2.5 concentration reached 118 ± 60 μg m^-3 during the study period, was approximately 3.4 times the United States Environmental Protection Agency 24-h standard. PM_2.5 concentration of Lhasa increased from 20:00 until 23:00, which was probably caused by space heating, waste incineration activities and decreased boundary layer at night. Furthermore, we found traditional religious butter lamp lighting of local Tibetan residents during festivals could cause PM_2.5 concentration to reach an alarmingly high level, 240 ± 30 μg m^-3. Therefore, to protect the atmosphere of Lhasa, the government may wish to conduct more complete monitoring and find ways to encourage clean heating and cooking fuels, enforce the supervision on illegal emission activities such as waste incineration, and guide residents to transfer to more environmentally friendly activities during festivals.