Refinery 1-hour SO2 NAAQS Non-Attainment SIP Air Quality Modeling Analysis Case Study

摘要

The current 1-hour National Ambient Air Quality Standard (NAAQS) of 75 parts per billion (ppb) for sulfur dioxide (SO2) was promulgated on June 22, 2010. Once a new NAAQS becomes effective, individual States have one year to recommend attainment or non-attainment status based either on ambient air monitoring data or on air quality modeling. In the case of the 1-hour SO2 NAAQS the initial timeline for the designation area status areas was due by June 22, 2011. Within two years of the effective date of the 1-hour SO2 NAAQS, the U.S. EPA was required to approve the States' proposed designations by June 22, 2013. For areas not attaining the 1-hour SO2 NAAQS, States were required to submit State Implementation Plans (SIPs) within 18 months of the determination of non-attainment areas. In the case of the 1-hour SO2 NAAQS, that meant that non-attainment SIPs were to be developed by December 22, 2013. Due to insufficient 1-hour air monitoring information, the U.S. EPA granted a 1-year extension for designating areas as non-attainment, pushing the timeline for development of non-attainment SIPs out by an additional year. During the fourth quarter of 2013 U.S. EPA designated several areas across the country as non-attainment for the 1-hour SO2 NAAQS based on ambient monitoring data. A refinery located in one of the areas designated as non-attainment was identified as the main SO2 emitter in the area. The non-attainment designation was based on 2009-2011 ambient air quality monitoring data from a SO2 monitor located 5 km to the northwest of the refinery (and with an elevation roughly 400 feet (ft) above the refinery). It was noted that the likely cause of the elevated SO2 concentrations at the ambient SO2 monitor was related to SO2 emissions from the refinery combined with inversion conditions. The refinery is located in a river valley, near complex terrain that creates conditions conducive to the formation of inversions, which may see an increased ambient concentration of a pollutant. With the new timeline, the refinery was required to assist the State in the development of a non-attainment SIP to demonstrate how the State proposed to bring the area into attainment for U.S. EPA approval. At that time the refinery contracted AIM Inc. (ALL4) to assist with the SIP process. The State requested that the refinery demonstrate attainment through emissions reductions established through ambient air quality modeling. Given the sensitivity-to meteorological conditions and the local topography, it was imperative to develop an appropriate meteorological dataset to use in the ambient air quality modeling. The refinery was the main SO2 emitter in the non-attainment area, and as such was required to demonstrate attainment through an air quality modeling demonstration. There is more control and flexibility when the air quality modeling demonstration is completed by the refinery as opposed to the State. This way, the refinery could evaluate multiple SO2 reduction strategies to demonstrate the most cost effective and operationally flexible scenarios for attaining the 1-hour SO2 NAAQS. This means that the refinery would also be responsible for the cost associated with the air quality modeling demonstration, and all of the challenges that would arise.