Fig. 3 depicts the details of total confirmed, active, recovered and deceased Covid–19 cases of India as on 5th May 2020. It can be observed that first case of Covid–19 was reported in India on 30th January 2020, however the rapid growth in Covid–19 cases was started in the last week of March and as on 5th May the total cases reached at 49,405. Out of which total active cases were 33571, recovered cases of 14140 and deceases cases of 1694. Thus the trend of Covid–19 pandemic in India is nearly 68% of active cases, and 27% of recovery rate with only 3.4% of fatality rate, which is much lower than many other countries.
3.2 Analysis of air quality index data
There have been some early suggestions that the spread and recovery of Covid–19 may vary with the change of seasons. Primarily it was also appeared to seem that the outbreaks of the new disease due to Covid–19 virus at different parts of the globe has an inclination for cool and dry conditions, though it is worth noting that the cases are found to spread severely in countries with a wide range of climates, including hot humid ones(Qi et al., 2020). Thus we approached to study the present situation of Covid–19 with the air quality in different places of India.The long-term exposure to the polluted air is dangerous for public health (Shaddick et al., 2018; Rovira et al., 2020). Particularly the diseases related with respiratory problems are more likely to be severe for the people living for decades in a region of fine particulate in air(Frontera et al., 2020; de Souza et al., 2018).As a result of fast economic growth and rising fossil fuel use, air pollution is now a major public health issue in the Asia-Pacific region.Therefore the air quality parameters are considered for analysis to find a correlation with total confirmed, activeand deceased Covid–19 casesin different parts of India. In the AQI data, six air pollutants were considered namely PM 2.5, PM10, NO2, SO2, CO, and Ozone. Although the National air quality index of CPCB consider eight pollutants, including particulate matter (PM 2.5, PM 10), sulphur dioxide (SO2), nitrogen dioxide (NO2), carbon monoxide (CO), ozone (O3), ammonia (NH3) and lead (Pb). But, the parameters ammonia (NH3) and lead (Pb) have not included in this study on account of insufficient data in the target cities. The air quality data of six important parameters have been collected for the month of December 2019. In cities with multiple monitoring stations, the arithmetic mean value of air quality parameters of all monitoring stations has been considered.
3.3 Correlation between air quality and Covid–19 cases
On observing and comparing the Fig.1 and Fig.2 one can easily realize that the spread of Covid–19 is not only and significantly associated with the population density in India. That is also a reason, which has driven us to consider the matter of prevailing air quality with Covid–19 spread in different places of India. Initially the Spearman and Kendallcorrelation coefficients between total covid–19 cases with seven AQI values for 25 cities are determined. The obtained coefficientvalues and the significance of each correlation coefficient value (with 95% confidence level and two tail test) are shown in Table 3. As per Spearman correlation test, the total Covid–19 cases are significantly correlated with pollutant AQI like PM 2.5, PM 10, SO2, and overall AQI. Out of them, PM 2.5 AQI has shown highest and most significant correlation (rs = 0.698; P value<0.001) followed by overall AQI (rs = 0.693; P value<0.001). However, the air quality parameters like NO2, CO and Ozone do not have any significant correlation with P value more than 0.005. The Kendall correlation test results also support the spearman correlation results. Similar to Spearman test, Kendall correlation test also indicates PM 2.5 AQI as the most influencing parameter (w = 0.850; P = 0.018) in total Covid–19 confirmed cases in India. The location wise variation between total confirmed Covid–19 cases and PM 2.5 AQI is depicted in Fig. 4. Sufficiently good agreement between total confirmed Covid–19 cases and PM 2.5 AQI can be observed in most of the considered location, resulting to highest correlation between them.
Table 3: The Spearman and Kendall correlation coefficients between air quality index variables with Total Covid-19 confirmed cases in different cities of India
|
AQI variables
|
Total Covid-19 confirmed cases
|
P value
|
Remarks
|
Spearman correlation coefficient (rs)
|
PM 2.5 AQI
|
0.698
|
<0.001
|
Significant
|
PM 10 AQI
|
0.567
|
0.004
|
NO2 AQI
|
0.359
|
0.078
|
Insignificant
|
SO2 AQI
|
0.500
|
0.001
|
Significant
|
CO AQI
|
0.381
|
0.061
|
Insignificant
|
Ozone AQI
|
0.021
|
0.923
|
Overall AQI
|
0.693
|
<0.001
|
Significant
|
Kendall correlation coefficient (w)
|
PM 2.5 AQI
|
0.850
|
0.018
|
Significant
|
PM 10 AQI
|
0.786
|
0.037
|
NO2 AQI
|
0.679
|
0.113
|
Insignificant
|
SO2 AQI
|
0.767
|
0.046
|
Significant
|
CO AQI
|
0.683
|
0.109
|
Insignificant
|
Ozone AQI
|
0.516
|
0.420
|
Overall AQI
|
0.845
|
0.019
|
Significant
|
Secondly the Spearman and Kendall correlation tests between active Covid–19 cases with seven AQI values of 25 locations are calculated, and correlation coefficients with their significance status are shown in Table 4. It is quite clear from both Spearman and Kendall correlation tests that active Covid–19 cases of 25 cities are also significantly correlated with air quality parameters like PM 2.5, PM 10, SO2, and overall AQI. That means active Covid–19 cases correlation coefficients are showing similar trends with the total confirmed Covid–19 cases. However the active Covid–19 case correlation coefficients are slightly lesser than the total confirmed Covid–19 cases. Here also, PM 2.5 AQI is found to be the most significant parameter affecting the active Covid–19 cases in both Spearman test (rs = 0.692; P value<0.001) and Kendall test (w = 0.847; P value = 0.018). PM 10 is found to be as the second most important parameter affecting the active Covid–19 casesby both Spearman (rs = 0.531; P value = 0.006)and Kendall test (w = 0.768; P value = 0.045). Thus it is clear that the particulate mattes have major impact on Covid–19 pandemic, and smaller the particle size higher is the risk factor. Primary gaseous air pollutants like NO2, CO and secondary air pollutants like Ozone do not have any significant impact on the spread of Covid–19 cases. The graphical representation of this close agreement between active Covid–19 cases and PM 2.5 AQI for 25 locations of India is shown in Fig. 5. Thus the importance of PM 2.5 in Covid–19 spread in India is clearly established.
Table 4: The Spearman and Kendall correlation coefficients between air quality index variables with active Covid-19 cases in different cities of India
|
AQI variables
|
Active Covid-19 cases
|
P value
|
Remarks
|
Spearman correlation coefficient (rs)
|
PM 2.5 AQI
|
0.692
|
<0.001
|
Significant
|
PM 10 AQI
|
0.531
|
0.006
|
NO2 AQI
|
0.294
|
0.152
|
Insignificant
|
SO2 AQI
|
0.502
|
0.010
|
Significant
|
CO AQI
|
0.329
|
0.108
|
Insignificant
|
Ozone AQI
|
‒0.083
|
0.693
|
Overall AQI
|
0.684
|
<0.001
|
Significant
|
Kendall correlation coefficient (w)
|
PM 2.5 AQI
|
0.847
|
0.018
|
Significant
|
PM 10 AQI
|
0.768
|
0.045
|
NO2 AQI
|
0.647
|
0.647
|
Insignificant
|
SO2 AQI
|
0.768
|
0.768
|
CO AQI
|
0.656
|
0.140
|
Ozone AQI
|
0.463
|
0.565
|
Overall AQI
|
0.840
|
0.020
|
Significant
|
It is well known that, long-term-exposure to high levels of PM2.5 is associated positively with deaths related to respiratory system. As in case of Covid–19, respiratory problems are considered to be key symptoms, hence there may be a relation between the Covid–19 death cases with the prevailing air quality of any particular area. Hence, the Spearman and Kendall correlations tests were performed between Covid–19 death cases with seven AQI values. Results shown in Table 5 clearly indicate strong correlation between particulate matters with the Covid–19 death cases. PM 2.5 AQI is found to be the most significant air quality parameter related to Covid–19 death cases(Spearman rs = 0.654 and P value <0.001; Kendall w = 0.832, P value = 0.022) followed by PM 10. It means the places in India with higher PM 2.5 concentration in air are experiencing higher deceased cases due to Covid–19 pandemic. The significant correlation between Covid–19 death cases and PM 2.5 AQI can also be observed from the Fig.6 for most of the considered cities in India.
Hence it can be concluded that PM 2.5 is the most critical air quality parameter affecting Covid–19 spread (total confirmed and actives cases) as well as deceased cases in different locations of India as depicted in Fig. 7. Similar results were also reported by few recent studies in USA (Wu et al., 2020; Bashir et al., 2020). Wu et al., 2020 has examined the association between long-term exposure to polluted air and COVID–19 deaths, they found a strong association between elevated PM2.5 and increased COVID–19 death rates. Probably long time exposure to PM 2.5 can reduce the people’s ability to fight against infectious diseases like COVID–19, resulting to higher death cases. Moreover, small size particulate matters can act as a carrier for Covid–19 virus, and resulting to higher spread of Covid–19 in the areas with higher PM 2.5 concentrations in the air.
Table 5: The Spearman and Kendall correlation coefficients between air quality index variables with deceased Covid-19 cases in different cities of India
|
AQI variables
|
Deceased Covid-19 cases
|
P value
|
Remarks
|
Spearman correlation coefficient (rs)
|
PM 2.5 AQI
|
0.654
|
<0.001
|
Significant
|
PM 10 AQI
|
0.610
|
0.001
|
NO2 AQI
|
0.367
|
0.071
|
Insignificant
|
SO2 AQI
|
0.514
|
0.009
|
Significant
|
CO AQI
|
0.435
|
0.030
|
Ozone AQI
|
0.203
|
0.331
|
Insignificant
|
Overall AQI
|
0.657
|
<0.001
|
Significant
|
Kendall correlation coefficient (w)
|
PM 2.5 AQI
|
0.832
|
0.022
|
Significant
|
PM 10 AQI
|
0.811
|
0.028
|
NO2 AQI
|
0.687
|
0.105
|
Insignificant
|
SO2 AQI
|
0.778
|
0.040
|
Significant
|
CO AQI
|
0.713
|
0.081
|
Insignificant
|
Ozone AQI
|
0.611
|
0.208
|
Overall AQI
|
0.832
|
0.022
|
Significant
|
Although results of this study reveal the strong correlation between prevailing PM 2.5 with the Covid–19 spread and deceased cases in Indian cities. However, it is too worth to mention that in addition to air quality, other weather/climatic parameters may play significant roles. Moreover, the societal and human behavioral factors, treatment and health infrastructure, and individual’s health immunity power are the other factors to be considered for a comprehensive analysis.