Particulate matter is the general term used for a mixture of particles (solid and liquid) suspended in the air, with a wide range of sizes and chemical compositions. PM2.5 refers to 'fine particles' that have a diameter of 2.5 micrometres (μm) or less. PM10 refers to particles with a diameter of 10 (μm) or less (see Figure 2.1). PM10 includes the 'coarse particles' fraction in addition to the PM2.5 fraction (EEA, 2013).
Diagram putting sizes of PM in context of human hair and beach sand. Taken from U.S. EPA 2010
Cardiovascular and lung diseases, heart attacks and arrhythmia's, central nervous system, systemic autoimmune rheumatic diseases (Bernatsky et al., 2015) and reproductive system effects. Can cause cancer, notably lung cancer (Raaschou-Nielsen et al., 2013) and lead to premature death (EEA, 2013). In the USA it is thought a reduction of 3.9 μg/m³ would prevent 7978 heart failure hospitalisations and save $300million a year (Shah et al., 2013). A study of 367,251 patients in europe found an increased Hazard ratio of 1.07 per 5 μg/m³ (Beelen et al., 2014). In the UK the effect on mortality is thought to be equivalent to 29,000 deaths every year (Defra, 2015). There is no recognised safe level of PM (WHO, 2013).
Affects animals in the same way as humans. Plant growth and ecosystem processes adversely affected. Can cause damage and soiling of buildings and reduces visability (EEA, 2013) (EEA, 2014).
Some PM lead to cooling and others lead to warming. BC is thought to be responsible for around 18% of total positive RF, primarily through darkening the surfaces of snow and ice covered areas. Can alter rainfall patterns (EEA, 2013).
Map showing number of deaths attributed to PM2.5 pollution per million of population in 2011. Original data from EEA, 2014, Figure created by wattsthecost.info