Sulfur dioxide air quality designations

The U.S. Environmental Protection Agency (EPA) establishes National Ambient Air Quality Standards (NAAQS) to protect human health and the environment. EPA evaluates how each area of the country complies with the standard during the process called “area designations,” also referred to as “air quality designations.”

Nearly all Washington counties comply with the NAAQS for sulfur dioxide (SO2). Ecology is currently collecting ambient air monitoring data for three counties in order to determine whether they meet the standard. Based on the preliminary data, an area in Whatcom County is at risk of violating the standard in 2020.

Federal air quality classifications

Under the federal Clean Air Act, if the air quality in a geographic area meets or is cleaner than the national standard, it is called an attainment area; areas that don't meet the national standard are called nonattainment areas. In some cases, EPA is not able to determine an area's status after evaluating the available information. Those areas are designated "unclassifiable."

If an area does not meet a standard, then the state is required to create and follow a state implementation plan to bring that area back into attainment.

Air quality designation process

In 2010, EPA established a new, lower SO2 standard. EPA evaluates and designates areas within three years of establishing a new standard. When the EPA’s 2010 designation process for SO2 was delayed, a federal court mandated deadlines to complete the process. The area designation process involves collecting relevant air quality data such as emissions, monitoring values, and modeling. States provide a recommendation to EPA on how each area should be designated. EPA considers that recommendation and public comments to make a final determination. If an area is designated as being in nonattainment, the state must meet federally mandated deadlines for fixing the air quality issues. For areas designated as attainment or unclassifiable there are no additional requirements besides ongoing regular monitoring.

Washington areas meeting federal SO2 standards

In Washington, EPA designated 36 counties in December 2017.
  • EPA agreed with our recommendation for 34 counties and designated them as being in "attainment/unclassifiable."
  • EPA designated two counties, Lewis and Thurston, as "unclassifiable," because of limited information.
  • The three remaining counties (Chelan, Douglas, and Whatcom) needed further investigation and were not a part of this round of designations.
In Lewis and Thurston counties, Ecology modeled emissions from the TransAlta coal-fired power plant to demonstrate the area continues to meet the standard. However, the EPA requested additional evaluations to support the proposed attainment designation. Due to resource constraints and the low risk of the area violating the standard, we chose to concur with EPA’s decision to designate the area as "unclassifiable."

Washington areas with ongoing SO2 monitoring

EPA required us to establish new SO2 monitors near facilities that emit more than 2,000 tons of SO2 a year and to collect data for three years (2017-2019). As a result, Ecology began monitoring SO2 concentrations around two aluminum smelters, one located in Whatcom County, and the other located in Chelan County, near the border with Douglas County.

Ecology outlined the siting of the new monitors in the 2016 Annual Monitoring Network Plan and solicited public comments in May-June 2016. You can read our report here:

Monitoring ambient air tells us how much SO2 is in the air at any given moment for a given location. However, advanced modeling and other technical analysis is required to fill in gaps and determine what sources are contributing. In Whatcom County, there are other industrial sources emitting SO2 near the Alcoa Intalco aluminum smelter. Some of these facilities are required to operate SO2 monitors. These monitors are showing lower readings that meet the SO2 standards. Ecology is taking into account all available data and performing technical analyses to pinpoint which sources are contributing to high readings at the SO2 monitors near Intalco.

We received questions about why monitoring SO2 pollution near the aluminum smelter in Malaga, Chelan County, was needed since the plant curtailed its operations starting in 2016-2017. Regulatory requirements do not allow us to postpone monitoring, and the facility may begin operating again. At this time, the monitor near the facility shows that SO2 readings are well below the NAAQS.

SO2 exceedances near Intalco, Whatcom County

The map below shows two monitors in the area of suspected highest concentration of SO2 pollution. 
The location of two air quality monitors outside the Intalco Aluminum smelter near Ferndale. 
Since we began monitoring SO2 pollution near the Intalco aluminum smelter, we recorded several exceedances of the SO2 standard in 2017 and 2018. With repeated exceedances, the area is at risk of violating the federal standard in 2020, which could lead to EPA designating the area as being in nonattainment. However, we believe that the size of the area impacted may be small based on Ecology’s preliminary air quality modeling analysis and lower SO2 readings at the SO2 monitors at the nearby Phillips 66 and BP refineries.

Nonattainment designation requires the state and local agencies to work together and submit a coordinated plan to EPA on how the area will achieve attainment within a defined timeframe. Failing to do so can trigger mandatory sanctions against the state.

Public health impacts

Breathing elevated levels of SO2 causes inflammation and tightening of airways, and can trigger asthma symptoms. SO2 typically dissipates very quickly, but people living or working close to the plant may have been exposed to short-term levels that pose a risk to those with preexisting breathing or health issues. At this time, we have no evidence that elevated levels of SO2 have reached Ferndale or other nearby communities.

We're performing additional analysis and reviewing data from the Phillips 66 and BP SO2 monitors to confirm this. In addition, the Northwest Clean Air Agency recently began operating an SO2 monitor near Eagleridge Elementary School in Ferndale. Information from all of these monitors will be considered in the analysis.

EPA established Air Quality Index (AQI) ratings for SO2 pollution to identify when the air quality becomes unhealthy. The table below provides a summary of number of days in each AQI category in 2017 and in 2018. 

Sulfur dioxide levels recorded near the Intalco facility

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As we analyze the data and model the distribution of potential impacts, we will know more about which areas pose a concern for air quality. Ecology, which oversees air quality permitting for Intalco, and the Northwest Clean Air Agency (NWCAA), which has overall responsibility for air quality in Whatcom County, may collect additional data to better understand the extent of the SO2 impact in the area. EPA will ultimately determine the nonattainment area boundary.

Ecosystem impacts

SO2 can also impair visibility in the form of haze and contribute to acid rain. 

Timeline for area designation

  • Spring 2020: Ecology validates three years of monitoring data
  • Spring-summer 2020: Ecology and NWCAA develop a joint recommendation to EPA on whether the area is meeting the standard. If not, the agencies will recommend a boundary for what parts of the county should be designated as being in nonattainment.
  • September 2020: EPA is expected to propose an area designation and hold a public comment period.
  • December 2020: EPA must finalize the designations.
  • March 2021: Designations become effective. For any nonattainment area, the regulatory “clock” to bring the area back into attainment begins.

Nonattainment designation

If part of Whatcom County is designated as being in nonattainment, Ecology and the Northwest Clean Air Agency will develop a plan to reduce emissions and bring the area back into attainment. This plan will be available for public review before submission to EPA. The plan must demonstrate that the area will meet the federal standard by March 2026 (or within 5 years of the effective date of the nonattainment designation).  

Ecology and Intalco are exploring air pollution control technology solutions to reduce future SO2 emissions from the facility, including investments in emissions reduction technology, such as installing a wet scrubber.

To learn more or follow the progress, sign up to Ecology’s SO2 attainment email list.