Abstract
Nearly 40 years of aerosol optical thickness (AOT) climate data record (CDR) derived from NOAA operational satellite Advanced Very High Resolution Radiometer (AVHRR) observation over the global oceans is used to study the AOT changes due to the COVID-19 lockdown over the surrounding coastal oceanic areas of 18 megacities in the coast zone (MCCZ). The AOT difference between the annual mean AOT values of 2020 with COVID-19 lockdown and 2019 without the lockdown along with the 2020 AOT annual anomaly are used to effectively identify the AOT changes that are a result of the lockdown. We found that for most of the 18 MCCZ, the COVID-19 lockdowns implemented to contain the spread of the coronavirus resulted in a decrease between 1% and 30% in AOT due to reduced anthropogenic emissions associated with the lockdowns. However, the AOT long-term trend and other aerosol interannual variations due to favorable or unfavorable meteorological conditions may mask AOT changes due to the lockdown effect in some MCCZ. Different seasonal variations of aerosol amount in 2020 relative to 2019 due to other natural aerosol emission sources not influenced by the lockdown, such as dust storms and natural biomass burning and smoke, may also conceal a limited reduction in the annual mean AOT due to the lockdown in MCCZ with relatively loose lockdown. This study indicates that the use of long-term satellite observation is helpful for studying and monitoring the aerosol changes due to the emission reduction associated with the COVID-19 lockdown in the surrounding coastal oceanic areas of MCCZ, which will benefit the future development of the mitigation strategy for air pollution and emissions in megacities.
Highlights
The coronavirus disease 2019 (COVID-19) pandemic, which affects the whole world, began in 2020 and has continued into 2021, causing a global public health and human life disaster that is unprecedented in this century [1,2]
Negative aerosol optical thickness (AOT) changes are anticipated as the lockdown consequence because anthropogenic pollution emissions are reduced due to reduced human activities during the lockdown period
40 years of AOT climate data record (CDR) derived from National Ocean and Atmospheric Administration (NOAA) Advanced Very High Resolution Radiometer (AVHRR) operational satellites observation over the global oceans is used to study the AOT changes due to the COVID-19 lockdown over the surrounding coastal oceanic areas of 18 megacities in the coast zone
Summary
The coronavirus disease 2019 (COVID-19) pandemic, which affects the whole world, began in 2020 and has continued into 2021, causing a global public health and human life disaster that is unprecedented in this century [1,2]. Air quality in urban and ambient suburban areas of these cities was altered unexpectedly to a different extent [7,8,9,10,11,12,13,14], especially in the megacities, which are normally influenced by heavy anthropogenic pollution due to active human activities (e.g., construction, transportation, energy generation, industrial production, and others) and pollution can be transported hundreds and even thousands of miles away under favorable meteorological conditions [15,16,17,18,19]. We define a megacity as a large urban agglomeration with a population exceeding 10 million inhabitants The majority of these urban megacities are located in a coastal zone or a zone with a distinct coastal influence [20], and are called Mega Cities in the Coastal Zone (MCCZ) hereafter.
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