Long-term trends in inorganic aerosol chemical composition and chemistry at an urban and rural site in the northeastern US.

Atmospheric nitrate and sulfate are major inorganic particulate matter components that impact human and ecosystem health and air quality. Over the last several decades, emissions of the precursor gases, nitrogen oxides (NO = NO + NO) and sulfur dioxide (SO), have dramatically decreased in the US in response to federal regulations. However, the response in concentrations of particulate nitrate (pNO) and sulfate (pSO) have not followed predictions due to complex non-linear chemistry feedbacks that may differ amongst environments (i.