Clean Air Act Amendments Research Articles

Quantifying US air pollution policy: How political and regional factors influence pollutant mitigation.

Air pollution control in the United States has evolved into a comprehensive policy system spanning from the federal to the state level over time. A unified quantitative analysis of policy intensity can shed light on the policy evolution across different levels, the influence of partisan and regional factors on policy, and the relationships with emissions of major pollutants. By harnessing the policy text of the Clean Air Act (CAA) at the federal level and State Implementation Plans (SIPs) at the state governments (1955-2020), we deployed a Natural Language Processing approach to define a policy intensity index to systematically quantify the US air policy landscape. Our findings highlight that the 1970 CAA amendment carries the most vigorous intensity as it established a holistic control system for the first time. Subsequent years witnessed a general trend of partisan polarization, eventually leading to a graduate convergence between red and blue states. Blue states demonstrated a closer alignment with federal directives and a superior efficacy in pollutant reduction. Regionally, the Northeast displays the highest overall policy intensity, and the West exhibits the highest coordination with the federal benchmarks, making these regions outperform others in air pollution control. Our study not only discusses policy implications for air pollutant reductions considering partisan and regional differences but also provides a novel measurement tool to quantify policies for assessing disparities and synergies.

An environmental justice analysis of air pollution emissions in the United States from 1970 to 2010

Over the last decades, air pollution emissions have decreased substantially; however, inequities in air pollution persist. We evaluate county-level racial/ethnic and socioeconomic disparities in emissions changes from six air pollution source sectors (industry [SO2], energy [SO2, NOx], agriculture [NH3], commercial [NOx], residential [particulate organic carbon], and on-road transportation [NOx]) in the contiguous United States during the 40 years following the Clean Air Act (CAA) enactment (1970-2010). We calculate relative emission changes and examine the differential changes given county demographics using hierarchical nested models. The results show racial/ethnic disparities, particularly in the industry and energy generation source sectors. We also find that median family income is a driver of variation in relative emissions changes in all sectors—counties with median family income >$75 K vs. less generally experience larger relative declines in industry, energy, transportation, residential, and commercial-related emissions. Emissions from most air pollution source sectors have, on a national level, decreased following the United States CAA. In this work, we show that the relative reductions in emissions varied across racial/ethnic and socioeconomic groups.

Trends in precipitation chemistry across the U.S. 1985–2017: Quantifying the benefits from 30 years of Clean Air Act amendment regulation

Acid rain was first recognized in the 1970s in North America and Europe as an atmospheric pollutant that was causing harm to ecosystems. In response, the U.S. Congress enacted Title IV of the Clean Air Act Amendments (CAA) in 1990 to reduce sulfur and nitrogen emissions from fossil fuel burning power plants. This study reports trends in wet-precipitation chemistry in response to emissions reductions implemented as part of the CAA. Trends were calculated for sulfate (SO4), nitrate (NO3) and ammonium (NH4) from 1985 to 2017 at 168 stations operated by the National Atmospheric Deposition Program (NADP); stations were divided into 9 regions across the United States. Trend analyses were conducted for three time periods: Period 1 (1985–1999), Period 2 (2000–2017), and the entire study period (1985–2017). Seasonal and regional Kendall trend analyses reveal significant decreasing trends in mean wet-precipitation SO4 concentrations in all 9 regions during the entire study period. The largest decreasing trends in monthly mean SO4 precipitation-weighted concentrations were measured in the Mid-Atlantic (−1.29 μeq/l/yr), Midwest (−1.15 μeq/l/yr), and Northeast regions (−1.10 μeq/l/yr). The trends in monthly mean NO3 concentrations were not as strong as those for SO4, but all of the regions had significant decreasing trends in NO3 and again the Mid-Atlantic (−0.53 μeq/l/yr), Midwest (−0.44 μeq/l/yr), and Northeast regions (−0.50 μeq/l/yr) had the strongest trends. Trends were steepest during Period 2 for SO4 and NO3, in fact for NO3 86% of the stations had significant decreasing trends during Period 2 while only 8% of the stations had significant decreasing trends during Period 1. The stations with the highest concentrations of SO4 and NO3 at the beginning of the study had the strongest decreasing trends and the relations were stronger during Period 2 than Period 1. For NH4, 22% of the stations had statistically significant increasing trends in concentration during Period 1. The largest increasing trends in wet-precipitation NH4 concentration occurred in the North-Central region during Period 1, Period 2 and throughout the entire study. By comparison, NH4 trends in the Rocky-North and Rocky-South regions were about half as steep and trends in the South-Central and Midwest regions were about one-third as steep.We compared trends in SO4 and NO3 concentrations from NADP stations to emissions of sulfur dioxide and nitrogen oxides, respectively to determine whether there was a relation between emissions and wet-precipitation concentration trends within proximity to NADP stations. There was a statistically significant relation (r2 = 0.62–0.69, p < 0.01) between the trend in SO4 concentrations at individual NADP stations and total and mean sulfur dioxide (SO2) emissions from power plants within a range of 750 km and 1000 km from each station. There were also significant relations between NO3 concentration trends at NADP stations and power plant emissions of nitrogen oxides, but they were not nearly as strong (r2 = 0.18–0.36, p < 0.01) as those for SO4 and were strongest for emissions within a range of 1000 km and 1500 km from each NADP station. Decreases in wet-precipitation SO4 concentrations were more consistent across regions and through time than decreases in NO3 and SO4 trends were more closely linked to stationary emissions sources than NO3 trends. There were statistically significant increases in NH4 wet-precipitation concentrations, as have been reported in previous studies, but this study found that those increases were strongest during Period 1 and were not consistent across the United States. During the first 3 years of the study period, wet-precipitation acidity was dominated by SO4 in 8 of the 9 regions; by 2017 NO3 dominated the acidity of wet-precipitation in 7 of the 9 regions. There has also been a downward shift in the NO3:NH4 ratio of wet-precipitation as the emissions of nitrogen oxides have declined while ammonia emissions have remained essentially constant. This shift has resulted in an increase in wet-precipitation total nitrogen concentrations in 7 of the 9 regions and indicate that efforts to control NH3 emissions will become increasingly important as emissions of nitrogen oxides continue to decline.

Reducing power sector emissions under the 1990 Clean Air Act Amendments: A retrospective on 30 years of program development and implementation

The 1990 Clean Air Act Amendments (CAAA) launched a new era in environmental protection. New provisions created the innovative Acid Rain Program to curtail acid-rain-causing emissions from the electric power sector through an allowance trading program. Success implementing this new type of program led to its expanded use to achieve additional power plant emission reductions in support of the CAAA "Good Neighbor" requirements. As a result, air pollution and its environmental effects have decreased dramatically in the last 30 years. Implementation of power plant regulations under the acid rain and Good Neighbor provisions of the CAAA provides insights into the efficacy of legislative versus regulatory policy and holds valuable lessons for future environmental policy.

Evaluation of the health impacts of the 1990 Clean Air Act Amendments using causal inference and machine learning

We develop a causal inference approach to estimate the number of adverse health events that were prevented due to changes in exposure to multiple pollutants attributable to a large-scale air quality intervention/regulation, with a focus on the 1990 Clean Air Act Amendments (CAAA). We introduce a causal estimand called the Total Events Avoided (TEA) by the regulation, defined as the difference in the number of health events expected under the no-regulation pollution exposures and the number observed with-regulation. We propose matching and machine learning methods that leverage population-level pollution and health data to estimate the TEA. Our approach improves upon traditional methods for regulation health impact analyses by formalizing causal identifying assumptions, utilizing population-level data, minimizing parametric assumptions, and collectively analyzing multiple pollutants. To reduce model-dependence, our approach estimates cumulative health impacts in the subset of regions with projected no-regulation features lying within the support of the observed with-regulation data, thereby providing a conservative but data-driven assessment to complement traditional parametric approaches. We analyze the health impacts of the CAAA in the US Medicare population in the year 2000, and our estimates suggest that large numbers of cardiovascular and dementia-related hospitalizations were avoided due to CAAA-attributable changes in pollution exposure.

Estimating Causal Effects of Particulate Matter Regulation on Mortality.

Estimating the causal effect of pollution on human health is integral for evaluating returns to pollution regulation, yet separating out confounding factors remains a perennial challenge. We use a quasi-experimental design to investigate the causal relationship between regulation of particulate matter smaller than 2.5 micrograms per cubic meter (PM2.5) and mortality among those 65 years of age and older. We exploit regulatory changes in the Clean Air Act Amendments (CAAA). Regulation in 2005 impacted areas of the United States differentially based on pre-regulation air quality levels for PM2.5. We use county-level mortality data, extracted from claims data managed by the Centers for Medicare & Medicaid Services, merged to county-level average PM2.5 readings and attainment status as classified by the Environmental Protection Agency. Based on estimates from log-linear difference-in-differences models, our results indicate after the CAAA designation for PM2.5 in 2005, PM2.5 levels decreased 1.59 micrograms per cubic meter (95% CI = 1.39, 1.80) and mortality rates among those 65 and older decreased by 0.93% (95% CI = 0.10%, 1.77%) in nonattainment counties, relative to attainment ones. Results are robust to a series of alternate models, including nearest-neighbor matching based on propensity score estimates. This analysis suggests large health returns to the 2005 PM2.5 designations, and provides evidence of a causal association between pollution and mortality among the Medicare population.

How did air quality standards affect employment at US power plants? The importance of timing, geography, and stringency.

We examine fossil-fuel power plant employment impacts of new nitrogen oxides (NOx) provisions under Title I of the 1990 Clean Air Act Amendments (CAAAs). These provisions required installation of reasonably available control technology (RACT) for NOx emissions for major stationary sources in the Ozone Transport Region and in more stringently classified ozone nonattainment areas. Standard approaches using nonattainment designation to identify regulatory impacts abstract from important implementation aspects such as when regulatory changes occur, where regulations are in effect, and which specific regulations apply. Omitting these factors can introduce bias by contaminating the control group, leading to underestimation of historical employment impacts and overestimation of projected impacts from tightening regulations. Our results indicate that the new NOx RACT requirements negatively impacted power plant employment. We find no significant impacts on generation, suggesting that installation of pollution controls may have contributed to labor-saving technical change at affected units.

Aluminum toxicity risk reduction as a result of reduced acid deposition in Adirondack lakes and ponds.

In 1990, the US Congress amended the Clean Air Act (CAA) to reduce regional-scale ecosystem degradation from SO x and NO x emissions which have been responsible for acid deposition in regions such as the Adirondack Mountains of New York State. An ecosystem assessment project was conducted from 1994 to 2012 by the Darrin Fresh Water Institute to determine the effect of these emission reduction policies on aquatic systems. The project investigated water chemistry and biota in 30 Adirondack lakes and ponded waters. Although regulatory changes made in response to the 1990 CAA amendments resulted in a reduction of acid deposition within the Adirondacks, the ecosystem response to these reductions is complicated. A statistical analysis of SO4, pH, Al, and DOC data collected during this project demonstrates positive change in response to decreased deposition. The changes in water chemistry also have lowered the risk of Al toxicity to brook trout (Salvelinus fontinalis [Mitchill]), which allowed the re-introduction of this species to Brooktrout Lake from which it had been extirpated. However, pH and labile aluminum (Alim) fluctuate and are not strongly correlated to changes in acid deposition. As such, toxicity to S. fontinalis also is cyclic and provides rationale for the difficulties inherent in re-establishing resident populations in impacted aquatic environments. Overall, aquatic ecosystems of the Adirondacks show a positive response to reduced deposition driven by changes in environmental policy, but the response is more complex and indicates an ecosystem-wide interaction between aquatic and watershed components of the ecosystem.

Who Benefits from Environmental Regulation? Evidence from the Clean Air Act Amendments

Abstract Using geographically disaggregated data and exploiting an instrumental variable strategy, we show that contrary to conventional wisdom, the benefits of the 1990 Clean Air Act Amendments (CAAA) were progressive. The CAAA created incentives for local regulators to target the initially dirtiest areas for cleanup, creating heterogeneity in the incidence of air quality improvements that favored lower-income households. Based on house price appreciation, households in the lowest quintile of the income distribution received annual benefits from the program equal to 0.3% of their income on average during the 1990s, over twice as much as those in the highest quintile.

EVALUATING THE IMPACT OF ENVIRONMENTAL POLICY ON THE TREND BEHAVIOR OF US EMISSIONS OF NITROGEN OXIDES AND VOLATILE ORGANIC COMPOUNDS

AbstractThe nature of this paper is a practical application of a proper time‐series methodology to evaluate policy impacts when there is uncertainty about the data being difference‐stationary (DS) or trend‐stationary (TS). We use this methodology to examine the trend behavior of two air pollutants, nitrogen oxides (NOX) and volatile organic compounds (VOC). In particular, we concentrate on answering two questions. First, were there breaks in the trends of NOX and VOC emissions around the same time environmental policies such as the Clean Air Act Amendments (CAAA) of 1970 were passed? And second, accounting for possible breaks are the US emissions of NOX and VOC TS or DS? Our empirical results show a clear evidence of a trend shift in NOX and VOC emissions at the time the CAAA of 1970 were passed, implying that this policy has been effective in reducing air pollution emissions, as well as additional breaks that correspond to other events and environmental policies before and after 1970. The unit root tests indicate that NOX are DS irrespective of the number of breaks in the trend whereas results for VOC emissions depend on the number of breaks assumed.

Potential Impact of Clean Air Act Regulations on Nitrogen Fate and Transport in the Neuse River Basin: a Modeling Investigation Using CMAQ and SWAT

There has been extensive analysis of Clean Air Act Amendment (CAAA) regulation impacts to changes in atmospheric nitrogen deposition; however, few studies have focused on watershed nitrogen transfer particularly regarding long-term predictions. In this study, we investigated impacts of CAAA NOx emissions on the fate and transport of nitrogen for two watersheds in the Neuse River Basin. We applied the Soil and Water Assessment Tool (SWAT) using simulated deposition rates from the Community Multiscale Air Quality (CMAQ) model. Two scenarios were investigated: one that considered CAAA emission controls in CMAQ simulation (with) and a second that did not (without). By 2020, results showed a 70 % drop in nitrogen discharge for the Little River watershed and a 50 % drop for the Nahunta watershed from 1990 levels under the with-CAAA scenario. Denitrification and plant nitrogen uptake played important roles in nitrogen discharge from each watershed. Nitrogen watershed response time to a change in atmospheric nitrogen deposition was 4 years for Nahunta and 2 years for Little River. We attribute these differences in nitrogen response time to contrasts in agricultural land use and diversity of crop types. Soybean, hay, and corn land covers had comparatively longer response times to changes in atmospheric deposition. The studied watersheds demonstrate relatively large nitrogen retention: ≥80 % of all delivered nitrogen.

The Transitional Costs of Sectoral Reallocation: Evidence From the Clean Air Act and the Workforce*

Abstract This article uses linked worker-firm data in the United States to estimate the transitional costs associated with reallocating workers from newly regulated industries to other sectors of the economy in the context of new environmental regulations. The focus on workers rather than industries as the unit of analysis allows me to examine previously unobserved economic outcomes such as nonemployment and long-run earnings losses from job transitions, both of which are critical to understanding the reallocative costs associated with these policies. Using plant-level panel variation induced by the 1990 Clean Air Act Amendments (CAAA), I find that the reallocative costs of environmental policy are significant. Workers in newly regulated plants experienced, in aggregate, more than $5.4 billion in forgone earnings for the years after the change in policy. Most of these costs are driven by nonemployment and lower earnings in future employment, highlighting the importance of longitudinal data for characterizing the costs and consequences of labor market adjustment. Relative to the estimated benefits of the 1990 CAAA, these one-time transitional costs are small.

When a Negative Externality Turns Positive: An Analysis of Flue-Gas Desulfurization By-Products

Energy and environmental regulations often result in the generation of unforeseen marketable by-products that can reduce costs of compliance. This research evaluates a unique case in which the marketability of by-products produces positive external benefits. Specifically, this paper focuses on flue-gas desulfurization (FGD) gypsum by-product produced by coal-fired electric plants using sulfur dioxide (SO2) scrubbing technology to comply with the emission standards set by the 1990 Clean Air Act Amendment (CAAA). Intuitively, the ability to market FGD gypsum provides incentives for electricity generating plants to operate their scrubbers more efficiently by providing gypsum revenues, and lowering gypsum disposal costs. Increased operating efficiency creates external benefits attributed to reduced SO2 emissions that would otherwise not have occurred. In order to estimate the impact of FGD gypsum marketability on SO2 emissions, a unique longitudinal database is constructed that merges electricity plants’ boiler-level SO2 emissions data from the U.S. Environmental Protection Agency (EPA) with data on scrubber operations and coal quality available from the U.S. Energy Information Administration (EIA). Boiler fixed-effect estimations suggest annual SO2 emissions decline by 3,494 tons as a result of gypsum marketing. This corresponds with a 39% average reduction in SO2 emissions at boilers marketing FGD gypsum. The total benefits associated with the reduced SO2 emissions are estimated between $147.1 billion and $350.6 billion (2011$), or between 0.9% and 2.1% of the total benefits of the U.S. CAA from 1990 to 2010.

Redistribution, Delegation, and Regulators’ Incentives: Evidence from the Clean Air Act

Taking advantage of the structure of the 1990 Clean Air Act Amendments (CAAA), we study the tradeoff between efficiency and equity associated with different levels of discretionary power when delegating regulatory authority to lower levels of government. Exploiting an instrumental variables approach, we provide evidence that the benefits of the 1990 CAAA were highly localized and accrued disproportionately to poorer households. Further, under the current structure of the 1990 CAAA, it costs at most about $1.30 for every $1 worth of air quality improvements transferred from richer to poorer areas, suggesting that the program does not entail a large tradeoff between efficiency and equity.

Did the Clean Air Act Amendments of 1990 really improve air quality?

The degree to which federal policies, such as the Clean Air Act (CAA), actually improve air quality is not fully understood. We investigate what portion of reductions in ambient fine particulate matter (PM2.5) that occurred 1999–2005 can be attributed to sulfur dioxide (SO2) and nitrogen oxide (NOx) emissions reductions from implementation of title IV, phase 2, of the 1990 CAA Amendments. A detailed statistical model links sources and receptors over time and space to estimate the relationship between changes in emissions and observed improvements in air quality. We employ relatively transparent statistical methods incorporating uncertainty bounds to complement point estimates of the complex physico-chemical fate and transport models commonly used to estimate source-receptor relationships associated with long-range emissions transport. Monitor-specific estimates of changes in PM2.5 from changes in emissions from individual power plants are highly significant and mostly of the expected relative magnitudes for distance and direction from sources; and the model performs well on out-of-sample forecasts. Although we observe substantial model uncertainty, using our preferred specification, we estimate that the title IV, phase II emissions reduction policy implemented 1999–2005 reduced PM2.5 in the eastern USA by an average of 1.07 μg/m3, roughly 8 % (standard deviation, 0.11 μg/m3) versus a counterfactual of no change in emission rates per unit of energy input. On a population-weighted basis, the comparable reduction in PM2.5 is 0.89 μg/m3, roughly 6 %. This model presents a practical tool that can be used for policy analysis of air quality.

The distributional effects of pollution regulations: Do renters fully pay for cleaner air?

Changes in housing prices play an important role in determining the incidence of environmental regulations: if the increase in value due to changes in environmental amenities is fully passed forward in the form of higher rental prices, renters may receive no net benefit from the regulations. To estimate the pass-through of the value of an environmental amenity, I exploit the reduction in suspended particulate matter (PM10) due to the 1990 Clean Air Act Amendments (CAAA). Using instrumental variables at varying levels of spatial aggregation I find that the 1990 CAAA led to a significant increase in rents, but the estimated percentage effect is about half as large as that of owner-occupied housing values. Little of this difference is driven by income differences between renters and homeowners; when stratifying by income and comparing the effect of the 1990 CAAA on housing values and rents, point estimates suggest that half of the increase in value is passed on to renters in the form of higher rents. This suggests that pass-through may be incomplete, but landowners still capture much of the value of the air quality regulations.

The Transitional Costs of Sectoral Reallocation: Evidence from the Clean Air Act and the Workforce

New environmental regulations lead to a rearrangement of production away from polluting industries, and workers in those industries are adversely affected. This paper uses linked worker-firm data in the United States to estimate the transitional costs associated with reallocating workers from newly regulated industries to other sectors of the economy. The focus on workers rather than industries as the unit of analysis allows me to examine previously unobserved economic outcomes such as non-employment and long run earnings losses from job transitions, both of which are critical to understanding the reallocative costs associated with these policies. Using panel variation induced by the 1990 Clean Air Act Amendments (CAAA), I find that the reallocative costs of environmental policy are significant. Workers in newly regulated plants experienced, in aggregate, more than $9 billion inforegone earnings for the years after the change in policy. Most of these costs are driven by non-employment and lower earnings in future employment, while earnings of workers who remain with their firm change little. Relative to the estimated benefits of the 1990 CAAA, these one-time transitional costs are small. However, the estimated costs far exceed the workforce compensation policies designed to mitigate some of these earnings losses.

Reassessing the Human Health Benefits from Cleaner Air

Recent proposals to further reduce permitted levels of air pollution emissions are supported by high projected values of resulting public health benefits. For example, the Environmental Protection Agency recently estimated that the 1990 Clean Air Act Amendment (CAAA) will produce human health benefits in 2020, from reduced mortality rates, valued at nearly $2 trillion per year, compared to compliance costs of $65 billion ($0.065 trillion). However, while compliance costs can be measured, health benefits are unproved: they depend on a series of uncertain assumptions. Among these are that additional life expectancy gained by a beneficiary (with median age of about 80 years) should be valued at about $80,000 per month; that there is a 100% probability that a positive, linear, no-threshold, causal relation exists between PM(2.5) concentration and mortality risk; and that progress in medicine and disease prevention will not greatly diminish this relationship. We present an alternative uncertainty analysis that assigns a positive probability of error to each assumption. This discrete uncertainty analysis suggests (with probability >90% under plausible alternative assumptions) that the costs of CAAA exceed its benefits. Thus, instead of suggesting to policymakers that CAAA benefits are almost certainly far larger than its costs, we believe that accuracy requires acknowledging that the costs purchase a relatively uncertain, possibly much smaller, benefit. The difference between these contrasting conclusions is driven by different approaches to uncertainty analysis, that is, excluding or including discrete uncertainties about the main assumptions required for nonzero health benefits to exist at all.

Comparison of the Effects of the US Clean Air Act and of Smoking Prevention and Cessation Efforts on the Risk of Acute Myelogenous Leukemia

We used 2 approaches based on published information to compare the impacts on leukemia incidence and benzene exposure of the 1990 US Clean Air Act (CAA) amendments and smoking prevention and cessation efforts. We extrapolated leukemia mortality related to community air pollution levels and to cigarette smoking from data from the US Environmental Protection Agency and the US Surgeon General. We also estimated relative decline in total exposures to benzene (a known human leukemogen) owing to the CAA amendments and to smoking prevention and cessation efforts. We estimated that because of the CAA, there will be approximately 300 fewer leukemia deaths in the United States during the period 2000 through 2020. During the closest comparable period (1987-2007), we estimated that decline in cigarette smoking led to 7120 fewer leukemia deaths, of which 1282 to 3702 were attributable to benzene. Similarly, the decline in smoking led to about a tenfold greater decrease in total-population benzene exposure than did the 1990 CAA amendments. Both the CAA and smoking cessation activities contribute to a decrease in leukemia incidence. Smoking cessation activities have had a greater effect in the past.

US Environmental Regulation and FDI: Evidence from a Panel of US-Based Multinational Firms

This paper measures the response of US-based multinationals to the Clean Air Act Amendments (CAAA). Using a panel of firm-level data over the period 1966–1999, I estimate the effect of regulation on a multinational's foreign production decisions. The CAAA induced substantial variation in the degree of regulation faced by firms, allowing for the estimation of econometric models that control for firm-specific characteristics and industrial trends. I find that the CAAA caused regulated multinational firms to increase their foreign assets by 5.3 percent and their foreign output by 9 percent. Heavily regulated firms did not disproportionately increase foreign investment in developing countries. (JEL F23, K32, L51, Q52, Q53, Q58)