Abstract. Hypoxia and adverse health outcomes might be affected by O3 pollution in the highland city of Lhasa. NOx emissions
can amplify the role of volatile organic compounds (VOCs) in the secondary
production of O3 under the conditions of high ultraviolet (UV)
radiation levels and unfavourable dispersion patterns in the Lhasa River
valley. Here, online C2–C11 VOC measurements, accompanied by other
parameters concerning the O3 chemical budget, were first obtained and
employed to identify the key VOC species and key sources of VOCs in terms of the loss rate against OH radicals (LOH), ozone formation potential (OFP), secondary organic aerosol potential (SOAP), and toxicity. Oxygenated VOCs (OVOCs) not only were the most abundant VOCs but also dominated LOH, OFP, and toxicity. Isoprene and anthropogenic VOCs were further identified as precursors of these OVOCs. Aromatics accounted for 5 % of the total VOCs (TVOCs) but contributed 88 % to the SOAP and 10 % to the toxicity. As the primary oxidative intermediates of aromatics were not well characterized
by our measurements, the environmental impact of aromatics could be
underestimated by our data. Source appointment and ternary analysis of
benzene, toluene, and ethylbenzene confirmed the combined contribution of
traffic emissions, solvent usage, and biomass burning. This suggests that
O3 precursors are mainly from sources associated with residents' lives,
except for solvent usage emissions which contribute to aromatics. Preliminary comparisons between source spectrums of transport sector emissions with positive matrix
factorization (PMF)-decomposed ones and our measured ones suggest that vehicle emission patterns of VOCs at high altitude generally follow the ground-level impression. More quantitative data are required to further confirm this point though. Emission reduction strategy analysis for O3 pollution control highlighted multiple benefits of the simultaneous reduction in NOx originating from
diesel vehicle emissions, biomass burning, and background sources
(possibly dominated by incense burning). The notable biogenic emission
contribution to the OFP was also first confirmed in our study, and this
highlights the side effects of the government's pursuit of a greener city.