Particulate Matter Aerosols

The study of atmospheric aerosols is important because of its adverse effects on health, air quality, visibility, cultural heritage, and Earth's radiation balance. Techniques that can help better characterize particulate matter are required to better understand the constituents, causes and sources of particulate matter (PM) aerosols.

Carbon is one of the main constituents of atmospheric aerosols. Radiocarbon (¹⁴C) measurement performed on aerosol particulate matter samples provide a means of quantitatively distinguishing the separate contributions to carbon in the sample from fossil-fuel and non-fossil-fuel-related sources via use of two component end member models to estimate the contributions of major carbon sources. The fossil carbon component is produced primarily from fossil fuel combustion, most commonly assigned to diesel engines and large stationary sources such as coal-fired power plants. The non-fossil component is a mixture of natural processes and anthropogenic activities (i.e. Biomass burning from wild fires, residential wood burning and campfires, secondary organic aerosols (SOA) from vegetation, and food cooking). The method depends on the fact that ¹⁴C is present at a small but measurable, approximately constant, level in living materials, but absent in fossil fuels. The two source categories are often referred to as fossil and biogenic carbon or fossil and contemporary carbon. Regarded as a tracer for "biogenic" sources ¹⁴C is extremely robust, retaining its identity throughout any atmospheric chemical changes.

At CAMS, we have used this capability to increase understanding of the sources of carbonaceous aerosols at National parks and urban sites. The high biogenic carbon content of PM in these studies was generally attributed to SOA whether they were collected at remote, rural or metropolitan sites. We have also found that at rural sites, the fossil component of PM does not vary much with the season while the fossil component of the PM is larger in the winter at the urban sites. We have also found that the fossil component of PM is greater at urban sites than rural sites, but the biogenic component is still usually larger. Most of the variation in PM carbon loading was due to swings in biogenic carbon contribution. We have also applied ¹⁴C source apportionment to the impact of haze in Yosemite National Park in California, USA (see figure) and have correlated an increase in haze with an increase in biogenic PM produced by forest fires hundreds of kilometers away from the sampling site.

Selected References