Clean Air Act (United States)

Summary

The Clean Air Act (CAA) is the United States' primary federal air quality law, intended to reduce and control air pollution nationwide. Initially enacted in 1963 and amended many times since, it is one of the United States' first and most influential modern environmental laws. As with many other major U.S. federal environmental statutes, the Clean Air Act is administered by the U.S. Environmental Protection Agency (EPA), in coordination with state, local, and tribal governments. EPA develops extensive administrative regulations to carry out the law's mandates. Associated regulatory programs, which are often technical and complex, implement these regulations. Among the most important, the National Ambient Air Quality Standards program sets standards for concentrations of certain pollutants in outdoor air, and the National Emissions Standards for Hazardous Air Pollutants program which sets standards for emissions of particular hazardous pollutants from specific sources. Other programs

Official source

https://en.wikipedia.org/wiki/Clean_Air_Act_(United_States)

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The influence of foreign vs. North American emissions on surface ozone in the US

As part of the Hemispheric Transport of Air Pollution (HTAP; < a href='http://www.htap.org' target='_blank'> http:// www.htap.org ) project, we analyze results from 15 global and 1 hemispheric chemical transport models and compare these to Clean Air Status and Trends Network (CASTNet) observations in the United States (US) for 2001. Using the policy-relevant maximum daily 8-h average ozone (MDA8 O-3) statistic, the multi-model ensemble represents the observations well (mean r(2)=0.57, ensemble bias = +4.1 ppbv for all US regions and all seasons) despite a wide range in the individual model results. Correlations are strongest in the northeastern US during spring and fall (r(2)=0.68); and weakest in the midwestern US in summer (r(2)=0.46). However, large positive mean biases exist during summer for all eastern US regions, ranging from 10-20 ppbv, and a smaller negative bias is present in the western US during spring (similar to 3 ppbv). In nearly all other regions and seasons, the biases of the model ensemble simulations are < 5 ppbv. Sensitivity simulations in which anthropogenic O-3-precursor emissions (NOx + NMVOC + CO + aerosols) were decreased by 20% in four source regions: East Asia (EA), South Asia (SA), Europe (EU) and North America (NA) show that the greatest response of MDA8 O-3 to the summed foreign emissions reductions occurs during spring in the West (0.9 ppbv reduction due to 20% emissions reductions from EA + SA + EU). East Asia is the largest contributor to MDA8 O-3 at all ranges of the O-3 distribution for most regions (typically similar to 0.45 ppbv) followed closely by Europe. The exception is in the northeastern US where emissions reductions in EU had a slightly greater influence than EA emissions, particularly in the middle of the MDA8 O-3 distribution (response of similar to 0.35 ppbv between 35-55 ppbv). EA and EU influences are both far greater (about 4x) than that from SA in all regions and seasons. In all regions and seasons O-3-precursor emissions reductions of 20% in the NA source region decrease MDA8 O-3 the most - by a factor of 2 to nearly 10 relative to foreign emissions reductions. The O-3 response to anthropogenic NA emissions is greatest in the eastern US during summer at the high end of the O-3 distribution (5-6 ppbv for 20% reductions). While the impact of foreign emissions on surface O-3 in the US is not negligible - and is of increasing concern given the recent growth in Asian emissions - domestic emissions reductions remain a far more effective means of decreasing MDA8 O-3 values, particularly those above 75 ppb (the current US standard).

2009

This study characterizes single-particle aerosol composition from filters collected during the ObseRvations of Aerosols above CLouds and their intEractionS (ORACLES) and CLoud-Aerosol-Radiation Interaction and Forcing: Year 2017 (CLARIFY-2017) campaigns. In particular the study describes aged biomass burning aerosol (BBA), its interaction with the marine boundary layer and the influence of biomass burning (BB) air on marine aerosol. The study finds evidence of BBA influenced by marine boundary layer processing as well as sea salt influenced by BB air. Secondary chloride aerosols were observed in clean marine air as well as in BB-influenced air in the free troposphere. Higher-volatility organic aerosol appears to be associated with increased age of biomass burning plumes, and photolysis or oxidation may be a mechanism for the apparent increased volatility. Aqueous processing and interaction with the marine boundary layer air may be a mechanism for the presence of sodium on many aged potassium salts. By number, biomass burning potassium salts and modified sea salts are the most observed particles on filter samples. The most commonly observed BC coatings are inorganic salts. These results suggest that atmospheric processes such as photolysis, oxidation and cloud processing are key drivers in the elemental composition and morphology of aged BBA. Fresh BBA inorganic salt content, as it has an important role in the particles' ability to uptake water, may be a key driver in how aqueous processing and atmospheric aging proceed.

COPERNICUS GESELLSCHAFT MBH2022

A tighter integration of modeling frameworks for climate and air quality is urgently needed to assess the impacts of clean air policies on future Arctic and global climate. We combined a new model emulator and comprehensive emissions scenarios for air pollutants and greenhouse gases to assess climate and human health co-benefits of emissions reductions. Fossil fuel use is projected to rapidly decline in an increasingly sustainable world, resulting in far-reaching air quality benefits. Despite human health benefits, reductions in sulfur emissions in a more sustainable world could enhance Arctic warming by 0.8 °C in 2050 relative to the 1995–2014, thereby offsetting climate benefits of greenhouse gas reductions. Targeted and technically feasible emissions reduction opportunities exist for achieving simultaneous climate and human health co-benefits. It would be particularly beneficial to unlock a newly identified mitigation potential for carbon particulate matter, yielding Arctic climate benefits equivalent to those from carbon dioxide reductions by 2050.

2022

The influence of foreign vs. North American emissions on surface ozone in the US

2009