COVID 19 Impact on worldwide NO2 Emission
In order to curb the transmission rate of the deadly virus and to flatten the curve of the spread of COVID-19 most countries have imposed restrictions such as shutting down offices, factories, schools, etc. and canceling all public events so as to avoid the possibility of any mass gathering which was bound to fan the spread even more. Many countries have requested their citizens to stay at home and to implement self-imposed travel restrictions, moving out of their houses only in case of emergencies or to facilitate absolute needs. As an obvious result of such lockdowns, there has been a considerable reduction in the road and air traffic which has further led to a reduction in emission of poisonous gases in the atmosphere due to a reduction in the consumption of fossil fuel and anthropogenic activities. Thus, in the light of this deadly epidemic it can be said that although there have been colossal and long-lasting social and economic impacts, the positive impact on the environment-howsoever temporary in nature-cannot be ignored.
Readings from the Sentinel-5 P from the Satelite imagery released by the European Space Agency clearly show that over the past 7 weeks, the levels of nitrogen dioxide (NO2) over cities and industrial clusters in the USA, Europe, and Asia were remarkably reduced, as evident from a comparison with last year. This decrease shall have several health benefits as NO2 released from automobiles, factories, etc. are a major cause of exacerbation respiratory illnesses such as asthma, bronchitis, and pneumonia and have decreased several thousand deaths related to respiratory deseases caused by the air pollution (Mirabellia et al., 2020; Venter et al., 2020; Annesi-Maesano et al., 2012; Szyszkowicz et al. 2014; Myllyvirta and Thieriot 2020; To et al. 2013; Watt 2006; Studnicka et al. 1997). Global tropospheric NO2 emission has been shown in Fig. 2 and 3 for the same period of the year 2019 and 2020, respectively.
Impact on the United States of America
It is observed that NO2 concentration has decreased by 50% in most parts of the North East, Southeast, and Midwest of the United States(US) during the studied time period (Fig. 4).From Fig. 4 it can be inferred that suspension of industry and activites during these seven weeks leadto reduction in consumption of fossil fuel and as a result it has improved the air quality of the US. Fig. 5 shows daily average NO2 emission of 2019 and 2020 for the North East, South East and Midwest regions of the US for the studied 7 weeks duration and confirms improvement in air quality.
Impact on European Countries
With the rapid escalation of CoVID-19 in Lombardy, Italy, the country which was the first in Europe to become a hotspot of the disease and declared complete lockdown on March 9, 2020, which was followed by Spain on March 14, issuing general confinement and further toughening the measures on 28 March; France declared complete lockdown on March 17 and Germany, rather, opted for strict social distancing measures since March 22, while the UK announced a complete lockdown on March 23 ("Coronavirus: What are the lockdown measures across Europe?" DW; 14.04.2020; and "When did the UK lockdown start and how long will it last? - Heart”; 28.05.2020). Comparing the mean NO2 emissions for the identical months and dates for the year 2019 and 2020 (Fig. 6 & 7) a unique observation is observed in the world context that the patches of highest concentration, of about 200 mol/km2 fell sharply lessthan150. In most of the other countries, although shades of concentrations lightened the kernel spots remained consistent. Declination of European nitrogen oxide emissions is unambiguously portrayed. Highest emission, during the lockdown, is spotted in Antwerp, Belgium followed by southwestern Cologne and Dortmund city of Germany and westerly neighboring Brussel, Netherland. These cities in the cluster, along with London, Paris, and Milan appear to emit the highest emission also during the year 2019. However, London, Paris, and Milan registered a very steep decline of NO2 emission in 2020. The prominent decline is also observed in Barcelona and Madrid of Spain. The precipitous decline could be attributed to the fact that a significant portion of the NO2 emission of most of these high yielding cities derives from traffic (Degraeuwe et al., 2017; Omrani et al., 2020; Ialongo et al., 2020; Ogen, 2020). It is estimated that more than 11,000 deaths have been avoided in Europe due to coal and oil consumption plummet during COVID-19 lockdown (Myllyvirta and Thieriot 2020; Ogen, 2020) .
Impact on India
In India, it's evident from both the figures (Fig. 8 & 9) that a significant and essential drop in NO2 emission is observed all over the country with the atypical exception in few northeastern states, where the subtle increase in the emission concentration is detected (Fig 8 & 9). The highest concentrations, during the lockdown period, are conspicuous to the coal excavated central-eastern sectors, while the industrial belt of Gujrat-Maharashtra appears to indicate reduced NO2 emission by more than 70%. Similar depletion is also observed in the central and southern states where the blistering NO2 concertation zones from 2019 appears mildewed or even nullified. The area in and around Delhi, considered as one of the worst air quality index cities by the World Meteorological Organization, has seen a significant drop in NO2 release. As such, all the hotspots of nitrogen oxides (Ghude et al., 2008, Ghudeet al., 2011) clearly show dramatic declination. The uninhabited or sparsely populated northern regions, quintessentially, show no difference. The temporal shutdown of industries and less traffic explains the considerable decrease, while for the coal-bearing zones, emission may be expected even without anthropogenic interventions. (Reference can be added)
Impact on China
The most subtle change in NO2 concentration, across the globe, is observed in China(Fig. 10). While NO2 emanation drastically declined in most of the industrial and populated cities across the globe, Beijing and its adjacent northern cluster of cities recorded the highest emanation in the world at a time when, almost, the whole world was under a lockdown or restricted public activity. Here, the efficacy of time series evaluation (Fig.11) plays a key role in distinguishing and elucidating the fall in emission. No perceptible variation in NO2 emission could be traced from the uninhabited terrains. In a nutshell, the NO2 emanating sources were actively functioning in China as usual years, as evidenced by the high emissions stemming from industrially captivated Beijing and its neighbored regions, with the remarkable exception of the Hubei province. With this premise, it may be inferred that China, well-nigh, operated its traffic and effluent emanating industries conventionally, diametric to global scenario. Incidentally, the prime reason for the eccentric pattern in global NO2 emission stems from China(Liu et al., 2020b; Ding, et al., 2020).
Further, the Hubei province is studied with supplementary inclusion of November and December 2019 and January to April 2020.
Impact on Wuhan (China)
Even as the scheming decline in NO2 emission is observed in China, the Hubei Province with Wuhan as its capital city, where the CoVID-19 case reportedly emerged for the first time (Lin et al., 2020), however, recorded a sharp fall. Such contrasting variation within similar geographical expanses prompted a localized study of mean NO2 emission in Hubei province. It is evident from the map that in January 2020 lowest ever emission is detected which sluggishly increased over the two months. Now, it is imperative to note that public traffic was suspended within Wuhan city on 23 January (Lin et al., 2020), showing stark inconsistency with the NO2 emission findings as shown in the map (Fig 12) and time-series variation (Fig 13).
Ideally, the declining volume of NO2 for a week could never average out the higher emission of the remaining three weeks to produce the lowest ever emission volume for the entire month of January 2020. However, the emissions were typically high during November and December 2019. The discordant correlation suggests that restriction in public traffic was imposed well before the last week of January, as known widely across the globe.