India has been one of the most polluted countries in the world with 6 cities in the top 10 polluted cities in the world as of 2019.Thus monitoring and assessing Air Quality is very important. So it is really necessary to quantify the impact of lockdown on Air quality and study it spatially in order to track its sources.

As per a study conducted every year approximately 1.2 million people died due diseases caused by air pollution. Thus a study like this was conducted so that it could help monitor and assess the causes.

According to National Ambient Air Quality Standards for India (NAAQS), a standardized index (Air Quality Index) is produced for the whole country of India based on the concentrations of various air pollutants such as – SO2, NO2, CO, O3 , PM2.5 , PM10 , NH3 and Pb. The concentration and effects of NH3 and Pb is not much when compared with other pollutants. Thus, for our current analysis we have chosen SO2, NO2, CO, O3 ,PM2.5 and PM10 pollutants. To quantity its impact on human health, the number of deaths due to various respiratory diseases were analyzed during the lockdown period.

Data Collection

SO2, NO2, CO and O3 were collected from Sentinel 5P dataset with spatial resolution of 7x3.5 km2 using Google Earth Engine. Sentinel-5 Precursor is a satellite launched on 13 October 2017 by the European Space Agency (ESA) to monitor air pollution. Javascript based coding was used to filter, extract and process satellite data on Google Earth Engine. As the PM2.5 and PM10 data is not available in Sentinel 5P, ground-monitoring stations were used for the same using Central Pollution Central Board (CPCB) portal. The data was collected for India as the analysis is also focused on the same.

Map Generation

QGIS software of version 3.12 was used for generation of maps for all the air pollutants for 5 phases i.e.

Before lockdown : 01 March 2020 to 07March

lockdown 1 : 25 March 2020 to 14 April

lockdown 2 : 15 April 2020 to 03 May

lockdown 3 : 04 May to 17 May

lockdown 4 : 18 May 2020 to 31 May

Geospatial Analysis

Firstly the changes in number of deaths due to various diseases caused by Air pollution was observed and statistical inferences are derived . Further analysis and change detection for SO2, NO2, PM10 and PM2.5 is carried out using Zonal Statistics tool from QGIS for identifying hotspot.

The changes in concentrations of all the previously mentioned pollutants are analyzed according to various phases of lockdown and are justified with the norms of lock down.

A) Sulphur Dioxide (SO2)

Sources : Sources include coal based electricity generation, industrial processes such as extracting metal from ore, natural sources such as volcanoes, and locomotives, ships and other vehicles and heavy equipment that burn fuel with high sulphur content.

Health Impact of SO2: A major consequence of increased sulphur dioxide in the atmosphere is acid rain where sulphur dioxide mixes with rainwater to create sulphuric acid rain.

HOTSPOT 1: Villupuram, Cuddalore, Vridhachalam (Tamil Nadu)

HOTSPOT 2: Singrauli (M.P), Sonbhadra (U.P), Surguja (Chhattisgarh)

(Maps are attached in the story map)

Observations regarding SO2

· The location of coal power plants were almost at the hotspots identified on SO2 map, giving an indication of possibility of coal combustion being an primary source for SO2.

·  A gradual decrease is observed in the values of SO2 at Hotspot1 till the 3rd lockdown.

·  A sudden increase in values may be the resultant of the relaxations given at Hotspot1.

·  A gradual decrease is also observed in values of SO2 at Hotspot2 till the 2nd lockdown, along with a sudden fluctuation in values in 3rd and 4th lockdown.

· Change in SO2 (Before lockdown to 4th lockdown): -46.08% at hotspot1 and -50.14% at hotspot2. 

B) Nitrogen Dioxide (NO2)

Sources :

It is produced from burning of fossil fuels,vehicle, making nitric acid, welding and using explosives, refining of petrol and metals, commercial manufacturing, and food manufacturing.

Health Impacts :The main health effect of nitrogen dioxide is on the respiratory system. Inhalation of nitrogen dioxide by children increases their risk of respiratory infection and may lead to poorer lung function in later life.

Looking at the hotspots in the map of NO2 (before the lockdown), the coal-based power plants were plotted there and is shown in the figure below.

HOTSPOT 1: Delhi, Ghaziabad and Gautam Buddha Nagar (U.P), Faridabad (Haryana).

HOTSPOT 2: Sidhi and Sonbhadra (M.P), Korba, Bilaspur, Raipur, Durg, Janjgir, Rajgarh, Jangir-Champu, Jharsuguda and Sambalpur (Chhatisgarh).

HOTSPOT 3: Bankur, Bardhhaman and Birkhum (West Bengal), Jamtara, Dhanbad and Bokara (Jharkhand)

(Maps are attached in the story map)

Observations regarding NO2 :

·  The location of coal power plants were almost at the hotspots identified on NO2 map, giving an indication of possibility of coal combustion being an primary source for NO2.

·  A gradual decrease is observed in the values of NO2 at Hotspot1 in the 1st lockdown, while the values kept increasing slowly till the 4th lockdown.

·  A gradual decrease is also observed in values of NO2 at Hotspot2 till the 2nd lockdown, along with a minor increase in values at 3rd and 4th lockdown, leading to higher value at 4th lockdown than values at before lockdown.

·  A gradual decrease is also observed in values of NO2 at Hotspot3 till the 3rd lockdown, along with a minor fluctuation in values in 3rd and 4th lockdown.

·   Change in NO2 (Before lockdown to 4th lockdown): -17.64% in hotspot1, 5.74% in hotspot2 and -22.77% in hotspot3.

C) Ozone (O3)

Source : It is created by chemical reactions between oxides of nitrogen (NOx) and volatile organic compounds (VOC). This happens when pollutants emitted by cars, power plants, industrial boilers, refineries, chemical plants, and other sources chemically react in the presence of sunlight

Health Impacts : Ozone in the air we breathe can harm our health. People most at risk from breathing air containing ozone include people with asthma, children, older adults, and people who are active outdoors, especially outdoor workers.

As Data available for Ozone is a continuous layer data hotspots cannot be identified hence a temporal study for years 2019 and 2020 is done.

(Maps are attached in the story map)

Observations Regarding O3 :

· An increasing trend is observed in India in both the years i.e. 2019 and 2020, as there is an increase in ozone in the indian subcontinent.

· As the levels of NO and NO2 has decreased in lockdown, the level of O3 has increased.

· But, as the level of NO2, NO has increased due to the relaxations given from 3rd lockdown, the level of O3 has shown a reducing trend in 2020 compared to the level of O3 in 2019.

· Change in O3 (Before lockdown to 4th lockdown): 6.7% in 2019, while -0.87% in 2020.

D) Carbon Monoxide (CO)

Sources :Other than incomplete combustion from vehicles, the major component of the CO anthropogenic emissions comes from biofuel use, which contributes 41% to the total anthropogenic emissions. The contributions from industrial, transportation and power plants sectors are estimated as 30%, 28%, and 1%, respectively. 

Health Impacts :The continuous exposure to the vehicular exhaust can lead to the symptoms of chronic CO intoxication, lower respiratory tract disorders such as cough, shortness of breath and pain with inspiration, blurry vision, difficulty in concentration, and confusion.

As Data available for CO is a continuous layer data hotspots cannot be identified hence a temporal study for years 2019 and 2020 is done.

(Maps are attached in the story map) 

Observations Regarding CO :

·  As the major sources of CO i.e. vehicular incomplete combustion and biomass burning has reduced due to lockdown, a decrease in the value of CO is observed in year 2020 while there was an increase in CO in year 2019.

· In 2020, a minor increase is seen in the 4th lockdown, as the possible result of the given relaxations.

· Even though the values at the end of 4th lockdown are higher in 2020 than in 2019, the percentage decrease is higher in 2020 compared to 2019.

· Change in CO (Before lockdown to 4th lockdown): -4.22% in 2019, while -4.64% in 2020.

E) PM2.5 and PM10

The air quality ground monitoring stations are situated in a clustered pattern, so we have used the interpolation within the particular clustered area rather than interpolating it for the whole India. So, as shown in the story map, four major cities like Delhi, Mumbai, Bangalore and Kolkata were selected, as they also have a good number of monitoring stations within the city.

(i) PM2.5

Sources : fine particles primarily come from car, truck, bus and other operations that involve the burning of fuels such as wood, heating oil or coal and natural sources. Some indoor sources of fine particles are tobacco smoke, cooking and operating fireplaces and fuel-burning space heaters. 

Health Impacts : Exposure to fine particles can cause short-term health effects such as eye, nose, throat and lung irritation, coughing, sneezing, runny nose and shortness of breath. Scientific studies have linked increases in daily PM2.5 exposure with increased respiratory and cardiovascular hospital admissions, emergency department visits and deaths.

Observations Regarding PM2.5:

· Before the lockdown, the value of PM2.5 was recorded highest for Delhi, while Bangalore had the lowest value.

· Till the 2nd lockdown, the values for PM2.5 for all cities have drastically decreased.

· After the 2nd lockdown, the value in Mumbai, Delhi and Bangalore have increased at a slower pace compared to Delhi.

· At the end of 4th lockdown, Delhi still has the highest value while Kolkata has the lowest values.

· Change in PM2.5 (Before lockdown to 4th lockdown): -83.28% in Kolkata,

-46.85% in Delhi, -54.93% in Mumbai while -38.86% in Bangalore.

(Graphs and maps are attached in Story Map)

(ii) PM10

Sources : . PM10 includes dust from construction sites, landfills and agriculture, wildfires and brush/waste burning, industrial sources, wind-blown dust from open lands, pollen and fragments of bacteria.

Health Impacts: Particles in the PM10 size range are commonly present in air and may be drawn into the body with every breath. In the lungs particles can have a direct physical effect and/or be absorbed into the blood. The specific effect of particles depends on their composition, concentration and the presence of other pollutants such as acid forming gases. 

Observations regarding PM10 :

· Before the lockdown, the value of PM10 was recorded highest for Delhi, while Kolkata had the lowest value.

· Till the 2nd lockdown, the values for PM10 for all cities have drastically decreased.

· After the 2nd lockdown, the value in Mumbai and Delhi increased while in Kolkata and Bangalore it decreased at a slower pace.

· At the end of 4th lockdown, Delhi is still leading (even more than the before lockdown values) while Kolkata had the lowest values.

· From the graph, we can compare the percentage change in PM10 values, which is as follows:

Change in PM10 (Before lockdown to 4th lockdown): -80.53% in Kolkata, 13.42% in Delhi, -63.281% in Mumbai, while -49.58% in Bangalore.

(Graphs and maps are attached in Story Map)

Visualization

The results in the form of maps , graphs and all the statistics are represented as a story map and a dashboard.

Inferences

For the said lockdown period in India, we have inferred the change in the concentration of the air pollutants at their respective hotspots. (Refer the figure below) To understand and analyze the impact of change in air quality on human health, the number of deaths caused due to various respiratory diseases were taken into account.Even though the number of respiratory diseases have increased, the rate of increase has drastically reduced during the lockdown period. This can be directly linked with the reduction in the concentrations of air pollutants at their respective hotspots. (Refer our story map).

Data regarding concentration of SO2, NO2, CO and O3 was collected from Sentinel 5P dataset with spatial resolution of 7x3.5 km2 and extracted and using Google Earth Engine. Sentinel-5 Precursor is a satellite launched on 13 October 2017 by the European Space Agency to monitor air pollution.

Link to story map : https://arcg.is/1uTH4K

Link for So2 , No2 ,CO , Ozone datasets :- https://developers.google.com/earth-engine/datasets/catalog

Link for PM2.5 and PM10 datasets :- https://app.cpcbccr.com/ccr/#/caagmdaashboard-all/caagmlanding

Other Resources :

1.Source of SO2 : https://www.downtoearth.org.in/news/air/india-emits-the-most-sulphur-dioxide-in-the-world-66230

2.Source of NO2 : https://www.mfe.govt.nz/air/specific-air-pollutants/nitrogen-dioxide#:~:text=The%20main%20source%20of%20nitrogen,commercial%20manufacturing%2C%20and%20food%20manufacturing.

3.Source of O3 : https://www.epa.gov/ground-level-ozone-pollution/ground-level-ozone-basics#:~:text=Ozone%20can%20be%20%E2%80%9Cgood%E2%80%9D%20or,ultraviolet%20radiation%20from%20the%20sun.&text=Ozone%20occurs%20both%20in%20the%20Earth's%20upper%20atmosphere%20and%20at%20ground%20level.

4.Source of O3 : https://cfpub.epa.gov/airnow/index.cfm?action=gooduphigh.index#:~:text=The%20troposphere%20generally%20extends%20to,harmful%20ultraviolet%20(UV)%20rays.

5.Impact of CO: https://pubmed.ncbi.nlm.nih.gov/29033981/

https://www.researchgate.net/publication/341040665_Effect_of_lockdown_amid_COVID-19_pandemic_on_air_quality_of_the_megacity_Delhi_India

6.Source of CO: https://agupubs.onlinelibrary.wiley.com/doi/full/10.1002/jgrd.50134#:~:text=It%20is%20found%20that%20the,and%20southern%20India%20(22%25).

Impact of CO: http://www.ipublishing.co.in/ijesarticles/fourteen/articles/volfive/EIJES51015.pdf

7.Source of PM2.5 : http://www.npi.gov.au/resource/particulate-matter-pm10-and-pm25#:~:text=Natural%20sources%20of%20PM10,storms%2C%20pollens%20and%20sea%20spray

8.Source of PM10: https://ww2.arb.ca.gov/resources/inhalable-particulate-matter-and-health#:~:text=PM10%20also%20includes%20dust%20from,pollen%20and%20fragments%20of%20bacteria.

9.Impact of PM10: http://www.npi.gov.au/resource/particulate-matter-pm10-and-pm25#:~:text=Natural%20sources%20of%20PM10,storms%2C%20pollens%20and%20sea%20spray

https://www.bbc.com/future/article/20200427-how-air-pollution-exacerbates-covid-19

Lockdown time intervals

Available at : https://en.wikipedia.org/wiki/COVID-19_pandemic_lockdown_in_India

10.Shagun Kapil (August 2019), “India emits the most sulphur dioxide in the world:, DownToEarth

Available at: https://www.downtoearth.org.in/news/air/india-emits-the-most-sulphur-dioxide-in-the-world-66230

11.“Nitrogen dioxide”, Ministry foe the Environment, New Zealand

Available at: https://www.mfe.govt.nz/air/specific-air-pollutants/nitrogen-dioxide#:~:text=The%20main%20source%20of%20nitrogen,commercial%20manufacturing%2C%20and%20food%20manufacturing.

12.“Ground-level Ozone”, Environmental Protection agency, United States.

Available at: https://www.epa.gov/ground-level-ozone-pollution/ground-level-ozone-basics#:~:text=Ozone%20can%20be%20%E2%80%9Cgood%E2%80%9D%20or,ultraviolet%20radiation%20from%20the%20sun.&text=Ozone%20occurs%20both%20in%20the%20Earth's%20upper%20atmosphere%20and%20at%20ground%20level.

13.“Good Up High Bad Nearby - What is Ozone?”, AirNow.

Available at : https://cfpub.epa.gov/airnow/index.cfm?action=gooduphigh.index#:~:text=The%20troposphere%20generally%20extends%20to,harmful%20ultraviolet%20(UV)%20rays.

14.Amit Kumar Gorai , Paul B Tchounwou, Gargi Mitra (2017), “Spatial Variation of Ground Level Ozone Concentrations and its Health Impacts in an Urban Area in India”, PubMed

Available at: https://pubmed.ncbi.nlm.nih.gov/29033981/

15.Susanta Mahato, Swades Pal, Krishna Gopal Ghosh (April 2020), “Effect of lockdown amid COVID-19 pandemic on air quality of the megacity Delhi, India”, ResearchGate

Available at: https://www.researchgate.net/publication/341040665_Effect_of_lockdown_amid_COVID-19_pandemic_on_air_quality_of_the_megacity_Delhi_India

16.Rajesh Kumar, Manish Naja, G. G. Pfister, M. C. Barth, G. P. Brasseur (January 2013), “Source attribution of carbon monoxide in India and surrounding regions during wintertime”, Advancing Earth and Space Science

Available at: https://agupubs.onlinelibrary.wiley.com/doi/full/10.1002/jgrd.50134#:~:text=It%20is%20found%20that%20the,and%20southern%20India%20(22%25).

17.Vibhor Sood , Shivani Sood, Pajesh Bansal, Umesh Sharma, Siby John (2014), “Traffic related CO pollution and occupational exposure in Chandigarh, India”, IJES

Available at: http://www.ipublishing.co.in/ijesarticles/fourteen/articles/volfive/EIJES51015.pdf

18.“Particulate matter (PM10 and PM2.5)”, Department of Agriculture, Water and the environment, Australian Government.

Available at: http://www.npi.gov.au/resource/particulate-matter-pm10-and-pm25#:~:text=Natural%20sources%20of%20PM10,storms%2C%20pollens%20and%20sea%20spray

19.“What is Particulate Matter 2.5 (PM2.5)?”, Eurpean Tech Serv NV.

Available at: https://etserv.be/glossary/particulate-matter-2-5-pm2-5/#:~:text=There%20are%20about%2025%2C000%20microns,the%20end%20of%20this%20sentence.

20.“Inhalable Particulate Matter and Health (PM2.5 and PM10)”, Air Resources Board, California.

Available at: https://ww2.arb.ca.gov/resources/inhalable-particulate-matter-and-health#:~:text=PM10%20also%20includes%20dust%20from,pollen%20and%20fragments%20of%20bacteria.