The layer presents the ambient NO2 state attainment status of air basins in California. Data from 2011.
Ambient air nitrogen dioxide concentrations are regulated by the state under the California Ambient Air Quality Standards (CAAQS) that apply for outdoor air.  In February 2007, the Air Resources Board established a new annual average NO2 standard of 0.030 ppm and lowered the one-hour NO2 standard to 0.18 ppm, after an extensive review of the scientific literature.  NO2 is a precursor to ozone.  Exposure to NO2 along with other traffic-related pollutants, is associated with respiratory symptoms, episodes of respiratory illness and impaired lung functioning. Studies in animals have reported biochemical, structural, and cellular changes in the lung when exposed to NO2 above the level of the current state air quality standard. Clinical studies of human subjects suggest that NO2 exposure to levels near the current standard may worsen the effect of allergens in allergic asthmatics, especially in children (http://www.arb.ca.gov/research/aaqs/caaqs/no2-1/no2-1.htm)  Oil and gas development activities utilizing hydraulic fracturing are known contributors to elevated concentrations of ambient nitrogen dioxide in the atmosphere.
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