Air Microbiome and Pollution: Composition and Potential Effects on Human Health, Including SARS Coronavirus Infection

Table 1

Recommendations and thresholds.

	WHO recommendations	EU thresholds	Chinese Ministry of Environmental Protection	United States EPA
PM2.5	10 μg/m^3 annual average	25 μg/m^3 annual average	35 μg/m^3 annual average	35 μg/m^3 averaged over 24 hours
	25 μg/m^3 24-hour maximum		75 μg/m^3 daily average
PM10	20 μg/m^3 annual average	40 μg/m^3 annual average	70 μg/m^3 annual average	150 μg/m^3 averaged over 24 hours
	50 μg/m^3 daily average	50 μg/m^3 daily average	150 μg/m^3 daily average
NO2	40 μg/m^3 annual average	40 μg/m^3 annual average	40 μg/m^3 annual average	53 parts per billion (ppb) annual mean
	200 μg/m^3 1-hour maximum	200 μg/m^3 1-hour maximum	80 μg/m^3 daily average; 200 μg/m^3 1-hour average
O3	100 μg/m^3 8-hour maximum	120 μg/m^3 8-hour average	160 μg/m^3 8-hour average; 200 μg/m^3 1-hour average	0.070 parts per million (ppm) averaged over 8 hours
SO2	20 μg/m^3 daily average	125 μg/m^3 daily average	60 μg/m^3 annual average; 150 μg/m^3 daily average	0.5 ppm averaged over 3 hours
	500 μg/m^3 10-minute maximum	350 μg/m^3 1-hour maximum	500 μg/m^3 1-hour average

Numbers in parentheses are the maximal numbers of allowed exceedances per year. Values applying for urban areas are shown. Stricter standards are required for special regions such as national parks. Numbers are according to the WHO [1], the EU [2], the Chinese Ministry of Environmental Protection [5], and the United States Environmental Protection Agency (EPA, values retrieved from https://www.epa.gov/criteria-air-pollutants/naaqs-table).