According to the European Union directives and Cabinet of Ministers' regulations, the maximum amount of particles with a diameter of up to 10 micrometers (PM10) in the air is 50 micrograms per cubic meter within a 24-hour-period, but the level may be exceeded on up to 35 days annually in Riga.
However, according to the Environment, Geology and Meteorology Center's data, there were 26 days in Riga during in January-April this year when the level was exceeded, and another 12 days thus far in May.
Usually, air pollution is the worst in March and April when weather is dry and sunny. Air quality tends to improve in May, but this year May has been exceptionally sunny and dry.
During the entire 2017, there were 30 days when the maximum amount of PM10 particulate matter in the air was exceeded in Riga, 39 in 2016, and 51 in 2015.