Particles from Outdoor Air

Ambient particle pollution is an important source of morbidity and mortality [39, 89-92]. Globally, an estimated 3.2 million deaths per year are attributable to ambient particle pollution [67]. A substantial fraction of people's exposures to particles from outdoor air occurs when people are indoors [49, 50, 93]; thus, climate-related changes in outdoor air particle levels will affect indoor particle exposures. There are numerous mechanisms through which climate change is expected to influence outdoor air particles [94]. For example, higher temperatures will speed the chemical reactions that produce some types of particles and also increase emissions of reactive organic chemicals from vegetation that lead to particles. Higher temperatures will also shift the partitioning toward more gases and fewer particles of other types. Increased overall global precipitation with climate change is expected to remove particles from the air, reducing airborne concentrations. Climate change will also affect winds, frequency of drought which influences wind-blown dust, wildfires, and mixing of pollutants in the atmosphere. One recent analysis predicts that climate change will substantially increase the frequency and duration of periods of air stagnation in much of the world, leading to more frequent periods with high concentrations of particles and other air pollutants [95]. At present; however, there is no consensus about the net effects of climate change on overall levels of ambient particles [10, 94, 96]. Effects are likely to vary regionally [62]. For North America in 2041 to 2050 relative to 1997-2006, Kelly, Makar [62] predicted quite small increases and decreases in particle concentrations. Given the high level of morbidity and mortality associated with outdoor air particles, even small fractional changes in particle levels could have substantial consequences for health. For the U.S., Tagaris et al. [88] projected 4000 deaths per year from climate-related increases in particles, which far outweighed their estimated 300 deaths per year from climate-related increases in ozone.