Table 2.
Overview of summary statistics of hourly PM2.5 concentration for five cities during lockdown period (25 March to 11 May 2020) for each year. n is the number of hourly averaged concentration data points for the above-noted duration after cleaning the data (Section 2.3). We estimated p-value using t-tests based on the hourly PM2.5 dataset for each year and they were found to be statistically significant (p-value <0.0001).
| Cities | Year | 2020 | 2019 | 2018 | 2017 | 2016 | 2015 |
|---|---|---|---|---|---|---|---|
| Chennai | Mean ± SD | 13 ± 10 | 19 ± 13 | 16 ± 12 | 23 ± 10 | 19 ± 11 | 19 ± 12 |
| Med (max) | 11 (95) | 17 (79) | 13 (370) | 22 (63) | 17 (165) | 16 (80) | |
| n | 1084 | 1095 | 1104 | 1063 | 909 | 923 | |
| ΔC1 (%) | – | –32 | –19 | –43 | –32 | –32 | |
| Delhi | Mean ± SD | 40 ± 24 | 84 ± 54 | 71 ± 43 | 84 ± 57 | 85 ± 79 | 68 ± 45 |
| Med (max) | 34 (195) | 71 (519) | 63(286) | 67 (470) | 62 (865) | 55 (395) | |
| n | 1152 | 1150 | 1145 | 1068 | 1150 | 1144 | |
| ΔC (%) | – | –52 | –44 | –52 | –53 | –41 | |
| Hyderabad | Mean ± SD | 31 ± 11 | 42 ± 17 | 54 ± 19 | 68 ± 26 | 52 ± 24 | 53 ± 22 |
| Med (max) | 30 (106) | 39 (137) | 50 (206) | 62 (207) | 49 (228) | 48 (222) | |
| n | 1142 | 1142 | 1066 | 1017 | 1123 | 907 | |
| ΔC (%) | – | –26 | –43 | –54 | –40 | –42 | |
| Kolkata | Mean ± SD | 29 ± 17 | 38 ± 16 | 43 ± 16 | 45 ± 13 | 42 ± 15 | 38 ± 19 |
| Med (max) | 25 (107) | 36 (115) | 40 (138) | 44 (172) | 39 (102) | 34 (129) | |
| n | 1151 | 1149 | 1031 | 1075 | 1121 | 1125 | |
| ΔC (%) | – | –24 | –33 | –36 | –31 | –24 | |
| Mumbai | Mean ± SD | 28 ± 11 | 31 ± 16 | 44 ± 22 | 46 ± 25 | 34 ± 19 | 44 ± 26 |
| Med (max) | 26 (74) | 28 (118) | 39 (195) | 39 (165) | 30 (217) | 38 (377) | |
| n | 1044 | 1141 | 947 | 980 | 977 | 1092 | |
| ΔC (%) | – | –10 | –36 | –39 | –18 | –36 |
1
ΔC = [(C2020 - C201x)/C201X] ×100 is the percent change of average PM2.5 in 2020 against the previous years.