&Emsp;In this study, we evaluated the variations of air quality in Lanzhou, a typical city inNorthwestern China impacted by the COVID‐19 lockdown. The mass concentration and chemicalcomposition of non‐refractory submicron particulate matter （NR-PM1）were determined by ahigh‐resolution aerosol mass spectrometer during January‐March 2020. The concentration of NR‐PM1dropped by 50% from before to during control period. The five aerosol components (sulfate, nitrate,ammonium, chloride, and organic aerosol [OA]) all decreased during the control period with the biggestdecrease observed for secondary inorganic species (70% of the total reduction). Though the mass concentration of OA decreased during the control period, its source emissions varied differently. OA fromcoal and biomass burning remained stable from before to during control period, while traffic andcooking related emissions were reduced by 25% and 50%, respectively. The low concentration during thecontrol period was attributed to the lower production rate for secondary aerosols.
&Emsp; By using a set of online instruments for mobile measurement, all instruments were calibrated according to standard methods before sampling. For example, the flow rate, size, and ionization efficiency (IE) of HR-ToF-AMS were calibrated according to the procedure described by Jayne et al. (2000). IE calibration uses NH4NO3and (NH4)2SO4to calibrate ammonium and sulfate, respectively. Sulfate is calibrated for IE separately. The CO2monitor is calibrated using high-precision and high-precision CO2standard gas
Experimentally obtained
&Emsp;Good quality of data
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CSTR:11738.11.NCDC.ZENODO.DB3948.2023
10.5281/zenodo.3855067