Atrocious Air

Download the report.

Background

Since the middle of the last century, the United States has witnessed significant changes in air quality, driven by industrialization, technological advancements, regulatory measures, and public awareness. The most important of these interventions was the Clean Air Act of 1963, which served as the first federal legislation addressing air quality concerns. While air quality has significantly improved from the first half of the 20th century, there are growing concerns that climate change impacts are undoing some of the progress the US has made through regulations and policy. This trend has been referred to as a “climate penalty”, whereby changing environmental conditions are inducing negative effects which erase some of the progress made through federal and local regulatory policies. Changes in environmental conditions, such as extreme heat, drought, and wildfires, are contributing to the increase in the levels of specific pollutants (O3 and PM2.5, specifically), often to concentrations above safe levels in much of the country. Even with significant cuts in anthropogenic emissions over the past decades, some research has projected that PM2.5 pollution will increase by as much as 50% over the next 3 decades in the Western United States.

The “climate penalty” is not felt equally across the country, with some of the most dramatic effects seen in recent upticks in PM2.5 from wildfire smoke in the West, and growing pockets of extreme Ozone exposure.  Historic station data from the EPA demonstrates that between 2000 and 2021, in the West, the number of Orange Days has increased by 477%, Red Days by 459%, Purple Days by 318%, and Maroon Days by 381%. In California alone, the average number of Green Days seen across the state has decreased from 136 to 93 (-32%), and the average number of Yellow Days has decreased from 200 to 146 (-27%). Subsequently, the average number of Orange Days has increased from 15 to 55 (+267%), Red Days increased from 10 to 16 (+60%), Purple Days increased from 1 to 17 (+1,600%), and Maroon Days from 3 to 38 (+1,167%).

Using the newly created First Street – Air Quality Model (FS-AQM), this report finds continued exposure as well as climate-related increases in poor air quality due to the growing incidence of wildfires, extreme heat events, and their negative interactions with other environmental and anthropogenic conditions. The results show that there are approximately 14.3 million properties (~10% of all properties) in the US that are estimated to have a week or more (7+ days) of unhealthy air quality days solely from PM2.5 in the current climate conditions. Of those, almost 5.7 million properties (~4%) may experience two or more weeks (14+ days) annually of smoke driven unhealthy air quality days. Some of the most at risk areas include large population centers such as Seattle, San Francisco, and Sacramento. It is important to understand the nature of this hazard, its link to climate, and the growing impact it will have on areas across the US into the future, including the growing negative effects on human health, labor force productivity, and even migration patterns.

Methodology

In order to build the First Street – Air Quality Model (FS-AQM), multiple sources of data were compiled, analyzed, and synthesized to create a single integrated model at a high resolution. The FS-AQM is driven by concentrations of the two pollutants whose variability is most clearly linked to climate change in the scientific literature, PM2.5 (from increasing wildfire smoke) and O3 (changes in air temperature and humidity). The model also includes a baseline level of anthropogenic PM2.5 to account for high levels of risk from anthropogenic sources like high density manufacturing, power plants, automobiles, and other drivers of non-climate related PM2.5 levels. 

In order to project O3 and PM2.5 into the future, the FSF-AQM relied on existing future smoke projections and downscaled Global Climate Models (GCMs). For the projection of PM2.5, the extrapolation requited the application of the ratio of future to current emissions as a multiplier to the daily PM2.5 wildfire concentrations from Childs et al. (2022) to create a representative 2050s time series, and repeated the summation of Orange+ AQI days to estimate the likely number of such days under future climate conditions. The future O3 projections were created by generating mid-century (~2054) O3 weather by statistically adjusting the 2006-2019 GridMET data to reflect the distribution changes between current and future conditions across an ensemble of 12 downscaled GCMs. Modeled projections are corrected by adjusting them with statistical scaling factors derived between current and future model output. This process preserves the underlying variability in the current time series while shifting the overall trend towards a future climate.

National Overview

The First Street – Air Quality Model (FS-AQM) finds that across the United States, over 83 million people, more than 25% of the population, are already exposed annually to air quality thresholds categorized as “unhealthy” by the Environmental Protection Agency’s (EPA) Air Quality Index (AQI). Among those at risk, nearly 10 million may have exposure to “very unhealthy” levels of air quality, and 1.5 million are at risk of experiencing “hazardous” air quality today. The most persistently impacted areas of the country are in the West where we have already seen an increase of nearly 2 times as many poor air quality days today compared to the beginning of the century. Places like California’s Central Valley, the San Francisco metro area, and much of Southern California are all expected to experience poor air quality up to 3 months worth of days in a bad year. In the future, major metro areas like Seattle and Portland are expected to see nearly two additional weeks of poor air quality, primarily due to the increasing occurrence of wildfires in the region. Overall, the increase in exposure is projected to be disproportionately seen in similarly large population centers. Over the next 30 years, the population exposed to “Unhealthy” Red Days is expected to increase by 51%, while the population exposed to “Very Unhealthy” Purple Days and “Hazardous” Maroon Days is expected to increase by 13% and 27%, respectively.