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Fig. 2 | Environmental Health and Preventive Medicine

Fig. 2

From: Coal burning-derived SO2 and traffic-derived NO2 are associated with persistent cough and current wheezing symptoms among schoolchildren in Ulaanbaatar, Mongolia

Fig. 2

Comparison of the outdoor SO2 concentrations in each district in each season. District A: box with stripes, district B: mesh box, district C: black box, district D: gray box; Asterisk indicates statistically significant (p < 0.05); air quality standard for the mean annual SO2 concentration: 10 μg/m3 (3.8 ppb)

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