Recent studies also show that Pb may be a factor in high blood pressure and subsequent heart disease. Lead can also be deposited on the leaves of plants, presenting a hazard to grazing animals. Home heaters and gas stoves also produce substantial amounts of NO2 in indoor settings. Long-term exposures to NO2 may lead to increased susceptibility to respiratory infection and may cause alterations in the lung. Nitrogen oxides also contribute to the formation of acid rain.
Some particles are large or dark enough to be seen as soot or smoke.
Others are so small they can be detected only with an electron microscope. Some particles are emitted directly from their sources, such as smokestacks and cars. Their chemical and physical compositions vary depending on location, time of year, and weather. Inhalable PM includes both fine and coarse particles. These particles can accumulate in the respiratory system and are associated with numerous health effects.