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Table 1 Frequency table of PM2.5 concentration by pollution class over the 534-day study period (July 11, 2013–May 31, 2015) in Nanjing, China. Days exceeding PM2.5 of 75 μg m−3 are considered “polluted,” i.e., higher than the national standard according to the Technical Regulation on Ambient Air Quality Index issued by the Ministry of Environmental Protection of People’s Republic of China (http://kjs.mep.gov.cn/hjbhbz/bzwb/dqhjbh/jcgfffbz/201203/W020120410332725219541.pdf)

From: Do green spaces affect the spatiotemporal changes of PM2.5 in Nanjing?

Daily PM2.5 (μg m−3) Pollution class No. of days and proportion (%) during the study period
Total Spring Summer Autumn Winter
0–35 Excellent 92 (17.2) 20 (21.7) 32 (34.8) 27 (29.4) 13 (14.1)
35–75 Good 247 (46.3) 84 (34.0) 51 (20.6) 60 (24.3) 52 (21.1)
Sub total   339 (63.5) 104 (30.7) 83 (24.5) 87 (25.6) 65 (19.2)
75–115 Light 115 (21.5) 23 (20.0) 10 (8.7) 38 (33.0) 44 (38.3)
115–150 Intermediate 43 (8.1) 5 (11.6) 2 (4.7) 17 (39.5) 19 (44.2)
150–250 Heavy 28 (5.2) 2 (7.1) 2 (7.1) 4 (14.3) 20 (71.5)
>250 Very heavy 9 (1.7) 0 (0.0) 0 (0.0) 0 (0.0) 9 (100.0)
Sub total   195 (36.5) 30 (15.4) 14 (7.2) 59 (30.2) 92 (47.2)
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