Scott Pruitt Nomination and EPA Approach to Interstate Transport Ozone Attainment

At this time there is quite a bit of noise about potential problems if Scott Pruitt is confirmed to head EPA because he would “hamstring EPA’s authority to set nationwide environmental standards”. As I understand it he is proposing to cooperate more with the states. This post describes a particular example where states proposed an alternative approach but in a recent action EPA continues to ignore the alternative proposed. I hope to show why I think that is a mistake. If Pruitt can get EPA to respond to this type of state action I support his nomination.

In my opinion one of the bigger air quality issues is ozone attainment, particularly as it relates to interstate transport. EPA explains that “air transport refers to pollution from upwind emission sources that impact air quality in a given location downwind”.  Emissions of nitrogen oxides (NOX) and Volatile Organic Compounds (VOC) can each undergo chemical reactions in the atmosphere to create ground-level ozone (smog) pollution.

The EPA website for interstate air pollution explains the “Good Neighbor” provision that requires EPA and states to address interstate transport of air pollution that affects downwind states’ ability to attain and maintain ambient standards. One of the reasons that the ozone limit has proved to be particularly difficult to attain is that the standard was recently tightened. In this example, I want to address the recent EPA Notice of Data Availability for the preliminary interstate ozone modeling data for this new limit.

EPA notes that they have completed preliminary interstate ozone transport modeling relevant for the 2015 ozone national ambient air quality standard. We are currently in the public comment period where the Agency is providing an opportunity for public review of this modeling data, including projected ozone concentrations and contributions for 2023, as well as projected emissions, including emissions from the power sector, that were used for this modeling.

In EPA’s approach the modeling projects ozone concentrations in 2023 at individual monitoring locations to determine the state-by-state contribution. EPA used a 2011-based air quality modeling platform which includes emissions, meteorology and other inputs for 2011 as the base year for the modeling and then projected the 2011 base year emissions to the 2023 base case scenario. The modeling domain covers the entire United States with a grid resolution of 12 km. I refer you to the technical support document for details of this modeling analysis.

I think that there are two glaring problems with EPA’s approach: one related to the emissions and one related to the air quality modeling. Both are related to the fact that the current ozone problem is episodic. Peak ozone concentrations only occur during several-day summertime hot and humid periods which also are periods of peak electrical demand.

EPA’s emissions approach goes to great lengths to project future year emissions at the expense of actual observed emissions. EPA uses the Integrated Planning Model, a massive proprietary planning model to project the emissions in future years. Because emissions are dependent upon fuel prices, technology, regulations, and energy use trying to estimate future emissions is a very complex undertaking and can only provide annual or seasonal average estimates. However, the primary concern are the peak periods and this model does not project these extreme periods well.

In order to address that problem the Eastern Regional Technical Advisory Committee was formed to prepare an alternative to the EPA emissions modeling approach. Basically the states and industry collaborated to develop an alternative based on adjustments to observed emission and operating rates. The result was Eastern Regional Technical Advisory Committee Electricity Generating Unit Emission Projection Tool. Importantly, this approach more accurately represents the actual and future emissions during ozone episodes than the EPA approach.  Unfortunately, this alternative approach was not used by EPA for this modeling.

Although EPA’s air quality modeling analysis is an impressive effort it also falls short of what I think is needed. As noted previously, EPA’s ozone projection methodology covers the entire United States on a 12 km by 12 km grid. My primary interest is New York State and the largest interstate impact of New York sources to ozone monitoring stations is downwind of New York City in Connecticut. I am convinced that the complex meteorological conditions during ozone episodes in this situation (land and sea breezes, elevated terrain concerns, and the nocturnal boundary layer structure along the coast) cannot be represented well enough to be accurate using such a coarse grid. Moreover, using that grid means that the many of the emissions are incorporated into the modeling at the same coarse grid resolution and there are indications that leads to further inaccuracies.

There is another problem with EPA’s modeling. They used a base year of 2011. As part of comments I developed to address the previous round of EPA interstate modeling, I compared daily New York electric generating unit emissions and observed ozone levels on an annual basis by running a regression to determine if there was a relationship. Not surprisingly there always was a statistically significant relationship. However what was interesting is that that strength of the relationship has changed recently. Prior to 2014 the regression analysis always indicated that there was a relatively strong relationship but in the last three years the relationship has deteriorated substantially. In order to accurately determine what is causing high ozone today a base year in the last three years is needed when this different regime of the relationship occurred.

I believe that in order to solve the interstate ozone transport problem it is first necessary to understand what is going on. EPA’s preliminary modeling described in their December 2016 Notice of Data Availability will not provide the necessary level of detail to describe the current situation. The Eastern Regional Technical Advisory Committee emissions modeling approach addresses one aspect that needs to be corrected. If Scott Pruitt’s approach to administering EPA would facilitate EPA using this alternative and modeling this problem differently then I believe his nomination should be supported.

Author: rogercaiazza

I am a meteorologist (BS and MS degrees), was certified as a consulting meteorologist and have worked in the air quality industry for over 40 years. Originally I worked for consultants doing air quality modeling work for EPA and then went to work with electric utilities where I was responsible for compliance reporting and analyzed the impact and efficacy of air quality regulations. I retired from working for one utility company full-time in 2010 and then worked part-time for most of the New York utility companies as the Director of an environmental trade association until my full retirement at the end of 2016. Environmental staff in any industry have to be pragmatic balancing risks and benefits and I hope my blog ( reflects that outlook. Jokingly our job description is to bring the companies we represent to the table so that they are not on the menu. Any of my comments on the web or posts on my blog are my opinion only. In no way do they reflect the position of any of my past employers or any company I was associated with.

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