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ENV-16-40 Identifying the Influence of Exceptional Events and International Transport: An Overview of When and How to Apply Clean Air Act Provisions for Background Ozone

Susan Kemball-Cook, Ramboll Environ

Format:
Electronic (digital download/no shipping)

Associate Member, International Member, Petrochemical Member, Refining Member - $0.00
Government, NonMember - $35.00

Description:

In October, 2015, the U.S. Environmental Protection Agency (EPA) promulgated a more stringent ozone National Ambient Air Quality Standard (NAAQS) of 70 parts per billion (ppb). The lowering of the standard from 75 ppb to 70 ppb makes it more likely that background ozone due to natural sources (e.g. wildfires, stratospheric ozone) or international transport can cause U.S. ozone monitors to exceed the NAAQS even when local emissions from human activities are minimal. Because background ozone is not controllable, the Clean Air Act (CAA) provides avenues for mitigating regulatory impacts of ozone due to emissions beyond local control. The Exceptional Events Rule states that if an exceedance of the ozone NAAQS can be shown to be caused by an uncontrollable, unusual event such as a wildfire or stratospheric ozone intrusion, the exceedance day may be excluded from the calculation of the monitor’s ozone design value1, potentially lowering the design value and even changing nonattainment status to attainment. If an area is shown to be influenced by transport from outside the U.S., CAA Section 179B may provide relief from some planning requirements and penalties for nonattainment areas where air quality would meet the NAAQS but for foreign anthropogenic emissions. In this paper, we outline methods for screening individual days in order to determine whether they may qualify for exclusion under the Exceptional Events Rule or for application of the Section 179B international transport rules. We present examples of the use of ambient monitoring data, satellite imagery and modeling to identify each type of event. We show how photochemical model ozone source apportionment tools (OSAT) are used to determine the geographic origin of ozone at a specific location and time and to quantify how much of that ozone comes from background ozone and how much from human activities. OSAT can further divide the contribution from human activities into contributions from different emissions categories such as vehicles, electric generating units, oil and gas, etc. We describe how the relevant analyses are assembled into a demonstration package for submission to EPA.

Product Details:

Product ID: ENV-16-40
Publication Year: 2016