Secondary Standards for Oxides of Nitrogen and Sulfur

EM – September 2022: This month, EM considers some of the challenges for the U.S. Environmental Protection Agency (EPA) during its review of the secondary standards for oxides of nitrogen and sulfur.
by Susan S.G. Wierman

Setting secondary National Ambient Air Quality Standards (NAAQS) to protect the public welfare has posed greater challenges for the U.S. Environmental Protection Agency (EPA) than Congress could have envisioned in 1970. EPA is considering whether to revise the current secondary standards for nitrogen dioxide (NO2) and sulfur dioxide (SO2). Both standards have remained unchanged since 1971, despite evidence they are inadequate to protect sensitive ecological resources.

The articles in this month's issue review the history of the secondary standards for NO2 and SO2, the water quality benefits of recent and forthcoming nitrogen oxide (NOx) emissions reductions, the urgency of additional NOx and SO2 emissions reductions to protect sensitive ecosystems, and advances in monitoring concentrations of total reactive oxides of nitrogen (NOy).

Continue reading the full September 2022 issue of EM.


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