Safety standards of particulate matter (PM) in ambient air in different geographical areas

World Health Organization (2018)20 μg·m−3 (annual)
50 μg·m−3 (24-h)
10 μg·m−3 (annual)
25 μg·m−3 (24-h)
US Environmental Protection Agency50 μg·m−3 (annual)
150 μg·m−3 (24-h)
12 μg·m−3 (annual)
35 μg·m−3 (24-h)
New South Wales Environment Protection Authority (Australia)25 μg·m−3 (annual)
50 μg·m−3 (24-h)
8 μg·m−3 (annual)
25 μg·m−3 (24-h)
UK and EUUK/EU: 40 μg·m−3 (annual)
50 μg·m−3 (24-h)#
UK: 25 μg·m−3 (annual)[30]
Scotland: 18 μg·m−3 (annual)
50 μg·m−3 (24-h)
Scotland: 10 μg·m−3 (annual)

PMx: particles with a 50% cut-off aerodynamic diameter of x µm. #: not to be exceeded more than 35 times a year in the UK; : not to be exceeded more than seven times a year in Scotland.