Abstract
Ningbo is a major coastal city in the Yangtze River Delta region, China, with the largest cargo capacity in the world. We conducted a field campaign in Ningbo to measure the impact of the COVID-19 lockdown on air pollutants including NO2, O3 and CO from 21 January to 23 March 2020, using a home-made low-cost sensor package. The average concentrations of NO2, O3 and CO were observed to be 7.2, 37.5 and 648.5 ppb, respectively, during the lockdown. Compared with the previous year, the concentrations of NO2 and CO decreased by 63.1% and 6.9%, while the concentration of O3 increased by 37.9%. The significant reduction of NO2 concentration may be attributed to the reduced emissions of freighters and heavy trucks with lower port cargo throughput, which led to a decrease of NO concentration. The increase of O3 concentration was probably due to the lower titration of O3 by NO. After the lockdown, the concentrations of O3 and NO2 increased by 15.5% and 143.1%, respectively, compared with those during the lockdown. The temporal variations of the concentrations of NO2, O3 and CO measured by the sensor package were coincident with those obtained by the reference apparatus, which proves the sensor package to be suitable for air quality monitoring in field campaigns. This is the first time that a dramatic decrease in NO2 concentration in a coastal city due to a lockdown has been reported.
Highlights
The COVID-19 lockdown was enforced by the Chinese government to prevent the spread of the coronavirus at the beginning of 2020 and included measures such as closingoff management, restricting traffic and closing public places
To verify the reliability of the sensor, five concentration gradients were compared between each sensor and the standard gas produced by the reference apparatus
The dramatic reductions of ambient NO2 concentration were only observed in the coastal city, which was mainly attributed to the reduction of ship-related air pollutants except for industrial and vehicle exhaust emissions
Summary
The COVID-19 lockdown was enforced by the Chinese government to prevent the spread of the coronavirus at the beginning of 2020 and included measures such as closingoff management, restricting traffic and closing public places. The concentrations of NO2 , CO and SO2 in some countries were observed to be decreased and the O3 concentration increased during the lockdown (Table 1). The exhaust emissions from freighters and heavy trucks for cargo transportation were considered to be the major sources of local air pollution in Ningbo [27,28,29]. We conducted a field campaign in Ningbo from 21 January to 23 March 2020 to study the impact of the COVID-19 lockdown on the air quality of the major coastal city using a home-made low-cost sensor package. The year 2019 is the closest year to 2020, and a comparison with 2019 can best reflect the impact of the COVID-19 lockdown on the air quality of Ningbo. We compared the temporal variations of the concentrations of NO2 , O3 and CO during the lockdown with the same period of the previous year and discuss the possible reasons for the variations of air pollutants
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