The World Health Organization (WHO) has published the first ever global air quality guideline standards for fine particles (PM), ozone, nitrogen dioxide and sulphur dioxide and called for world-wide action to reduce air pollution. Several are stricter than similar WHO guidelines for Europe published in 2000. It recommends maximum 20 micrograms per cubic metre (ug/m3) over 24 hours for SO2, compared with 125 ug/m3 previously, and 100 ug/m3 over eight hours for ozone, compared with 120 ug/m3 previously. Also included are detailed guidelines for fine particles, which were previously omitted.
See WHO Press Release