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. To prevent the spread of the COVID-19 epidemic, restrictions such as“lockdowns” were conducted globally, which led to a significant reductionin fossil fuel emissions, especially in urban areas. However, CO2concentrations in urban areas are affected by many factors, such as weather,biological sinks and background CO2 fluctuations. Thus, it is difficultto directly observe the CO2 reductions from sparse ground observations.Here, we focus on urban ground transportation emissions, which weredramatically affected by the restrictions, to determine the reductionsignals. We conducted six series of on-road CO2 observations in Beijingusing mobile platforms before (BC), during (DC) and after (AC) theimplementation of COVID-19 restrictions. To reduce the impacts of weatherconditions and background fluctuations, we analyze vehicle trips with themost similar weather conditions possible and calculated the enhancementmetric, which is the difference between the on-road CO2 concentrationand the “urban background” CO2 concentration measured at the tower ofthe Institute of Atmospheric Physics (IAP), Chinese Academy of Sciences. Theresults showed that the DC CO2 enhancement was decreased by 41 (±1.3) parts per million (ppm) and 26 (±6.2) ppm compared to those forthe BC and AC trips, respectively. Detailed analysis showed that, duringCOVID-19 restrictions, there was no difference between weekdays and weekendsduring working hours (09:00–17:00 local standard time; LST). The enhancementsduring rush hours (07:00–09:00 and 17:00–20:00 LST) were almost twice thoseduring working hours, indicating that emissions during rush hours were muchhigher. For DC and BC, the enhancement reductions during rush hours weremuch larger than those during working hours. Our findings showed a clearCO2 concentration decrease during COVID-19 restrictions, which isconsistent with the CO2 emissions reductions due to the pandemic. Theenhancement method used in this study is an effective method to reduce theimpacts of weather and background fluctuations. Low-cost sensors, which areinexpensive and convenient, could play an important role in further on-roadand other urban observations.

Observed decreases in on-road CO&lt;sub&gt;2&lt;/sub&gt; concentrations in Beijing during COVID-19 restrictions

Observed decreases in on-road CO<sub>2</sub> concentrations in Beijing during COVID-19 restrictions