On February 25, 2019, the Environmental Protection Agency (EPA) announced that it would neither raise nor lower the National Ambient Air Quality Standards (NAAQS) for sulfur dioxide (SO2) pollution last updated in 2010 under the Obama Administration, concluding that the existing standard was both necessary and sufficient for protecting human health. This means that the current standard of 75 parts per billion of SO2 in the ambient air will remain in place for the foreseeable future.
Sulfur dioxide, a pollutant produced during the burning of coal, oil and gas, is primarily produced by traditional electric power plants, industrial processes, and motor vehicles. A nose, throat and lung irritant, SO2 can cause adverse health effects such as wheezing, shortness of breath and chest tightness, and is especially problematic for asthmatics, children, and the elderly.
EPA is required by Section 109 of the Clean Air Act (CAA) to set NAAQS for six "criteria pollutants," including SO2, at levels that are protective of human health, allowing an adequate margin of safety. On June 8, 2018, the EPA proposed the current action in a proposed rule, for which it received multiple public comments. Health advocacy organizations, including the American Lung Association, had advocated lowering the SO2 NAAQS to 50 ppb, while industry groups such as the American Petroleum Institute had argued that the existing NAAQS were too stringent.
In its final rule enshrining the decision to keep the existing SO2 NAAQS in place, EPA concluded that health effects evidence made available since the review leading to the 2010 NAAQS is consistent with, but does not substantially alter the conclusions of, evidence available in that last review, and "continues to demonstrate a causal relationship between relevant short-term exposures to SO2 and respiratory effects, particularly with regard to effects related to asthma exacerbation in people with asthma."