High contribution of vehicle emissions to fine particulate pollutions in Lanzhou, Northwest China based on high-resolution online data source appointment

Changes in physical and chemical properties of urban atmospheric aerosols and ozone during the COVID-19 lockdown in a semi-arid region

“…Higher reduction in NO 2 than SO 2 indicated higher reduction of vehicular emissions and weak reduction of industrial emissions. NOx reduced by 53.6% at LACMS ( Table S1 ), where vehicular emissions were estimated to be the largest contributor (36.0%) to PM 2.5 in winter ( Wang et al, 2021 ). Significant reductions in gaseous pollutants and PM 2.5 indicated large reductions of anthropogenic emissions during the COVID-19 lockdown in Lanzhou.…”

“…Higher reduction in absorption than scattering was attributed to reduction in primary emissions of both scattering and absorbing species while enhanced secondary aerosols were mainly scattering species. Vehicular emitted EC was the main absorbing species at LACMS during winter ( Wang et al, 2021 ). Thus, the reduction in absorption was mainly caused by reduced vehicular emissions during the lockdown.…”

“…The increase in O 3 concentration increased the oxidation capacity of the atmosphere and thus enhanced the formation of secondary organic/inorganic aerosols, which has been suggested by previous studies based on numerical modelling and observation data (e.g., Chan et al, 2017 ; Wang et al, 2016 ; Huang et al, 2020 ; Kang et al, 2021 ; Le et al, 2020 ; Li et al, 2021 ). The secondary formed inorganic aerosols and most of the organic aerosols were efficient in scattering and inefficient in absorbing the solar radiation, leading to higher SSA of the total atmospheric aerosols ( Deng et al, 2016 ; Wang et al, 2021 ). In turn, aerosols with higher SSA relatively absorbed less while scattered more solar radiation, which promoted the formation of O 3 ( Liu et al, 2019 ; Ma et al, 2021a ).…”

“…The source apportionment was conducted using the Positive Matrix Factorization (PMF) 5.0 model, technical details are available in a previous study ( Wang et al, 2021 ) and in the Supplementary materials. The tropospheric ultraviolet radiation (TUV) model, which was jointly developed by Madronich and Flocke (1998) to calculate the tropospheric ultraviolet radiation and some of the visible radiation, was also used.…”

“…Lanzhou is a typical valley city in the semi-arid region of northwest China, where coal is the main fuel used for residential heating in winter ( Tan et al, 2017 ). Previous studies suggest that secondary inorganic aerosols (SIAs) in Lanzhou in winter were mainly from photochemical reactions ( Du et al, 2020 ) and motor vehicle emissions were a major contributor to PM pollution in Lanzhou ( Wang et al, 2021 ). A recent study revealed that PM 1 reduced by 50% during the lockdown, mainly contributed by the reduction in secondary species ( Xu et al, 2020 ).…”