Abstract
Spraying roads with water on a large scale in Chinese cities is one of the supplementary precaution or mitigation actions implemented to control severe air pollution events or heavy haze-fog events in which the mechanisms causing them are not yet fully understood. These air pollution events were usually characterized by higher air humidity. Therefore, there may be a link between this action and air pollution. In the present study, the impact of water spraying on the PM2.5 concentration and humidity in air was assessed by measuring chemical composition of the water, undertaking a simulated water spraying experiment, measuring residues and analyzing relevant data. We discovered that spraying large quantities of tap or river water on the roads leads to increased PM2.5 concentration and humidity, and that daily continuous spraying produces a cumulative effect on air pollution. Spraying the same amount of water produces greater increases in humidity and PM2.5 concentration during cool autumn and winter than during hot summer. Our results demonstrate that spraying roads with water increases, rather than decreases, the concentration of PM2.5 and thus is a new source of anthropogenic aerosol and air pollution. The higher vapor content and resultant humidity most likely create unfavorable meteorological conditions for the dispersion of air pollution in autumn and winter with low temperature.
Highlights
Numerous severe air pollution events have occurred in China since 2013
The results suggest that both tap water and river water contain sulfate, ammonia, nitrates, and other compounds, and these components are expected to inevitably end up on the road surface or in the air when the two types of water are sprayed on roads
When water was sprayed on roads at air temperatures of 5 to −5 ◦ C (Figure 3). These results indicate that severe air pollution events commonly occurred in autumn and winter because of the low temperatures and high humidity
Summary
Numerous severe air pollution events have occurred in China since 2013. For example, in the Beijing, Tianjin and Hebei (BTH) region, severe air pollution events occurred during21.7 days in January 2013 [1,2,3,4,5,6,7,8]. Numerous severe air pollution events have occurred in China since 2013. In the Beijing, Tianjin and Hebei (BTH) region, severe air pollution events occurred during. (3) They are recurring, and a typical severe air pollution event lasts approximately 6–9 days and can be divided into three stages: an accumulative rising stage (PM2.5 rising from 50 to 200 μg/m3 and humidity reaching 60%, lasting for 3–4 days); the peak stage (sharp increases in the PM2.5 level, sometimes increasing by several times in 1 h and reaching concentrations as high as 700 μg/m3 ; humidity exceeding 80%; lasting for 2–3 days); and a declining stage (featuring a cold wind or rain and decreases in both PM2.5 and humidity, returning to sunny conditions within 1 day). 45% or more of the peak stage formed rapidly within 1–9 h, and approximately 50% of severe air pollution events quickly declined from the sixth pollution level (AQI > 300) to the second pollution level (AQI 51–100) within
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