San Francisco Bay Area 2004 State Implementation Plan Revision Project

The Bay Area Air Quality Management District (BAAQMD or District) is responsible for monitoring ambient air quality within the nine San Francisco Bay Area counties (Bay Area or SFBA), and for developing and enforcing emission control plans for those pollutants that have violated the National Ambient Air Quality Standards (NAAQS) and the California Ambient Air Quality Standards (CAAQS) within its jurisdiction.  Based upon historical air quality measurements within the Bay Area “airshed”, the U.S. Environmental Protection Agency (EPA) has designated the SFBA as being in non-attainment of the federal 1-hour ozone standard.  Over the years, the BAAQMD has developed and submitted several implementation plans to control ozone in the Bay Area.  These plans have been effective in reducing ambient ozone levels, and since 1995 the Bay Area 1-hour ozone design value has been reduced to near the federal standard.  On April 22, 2004, the EPA determined that the SFBA has attained the 1-hour ozone NAAQS.  The original 1-hour ozone standard has now been effectively replaced by a new and more stringent 8-hour ozone standard, and based upon air quality levels within the SFBA between 2001-2003, the area has been designated as a marginal non-attainment area of the federal 8-hour standard.  Furthermore, the BAAQMD, the California Air Resources Board (CARB) and districts downwind of the SFBA have continued interest in analyzing the role of regional transport of ozone and precursors. 

Given the complexities surrounding the formation and fate of ozone, the development of control strategies to mitigate precursor emissions is always a technically challenging endeavor.  As a result, EPA guidance on ozone SIP development requires that nonattainment areas undertake photochemical computer modeling to understand the idiosyncrasies of their area’s ozone problem, as well as to develop and evaluate ozone response to the various control scenarios under consideration.  Furthermore, EPA and CARB guidance requires the development of a detailed Modeling Protocol that establishes an acceptable methodology to apply and evaluate today’s state-of-the-science photochemical models and to develop various supporting datasets.

Recognizing the need to maintain a current state-of-the-science photochemical modeling capability to address the various on-going regulatory activities within the SFBA and throughout central and northern California, the BAAQMD and their contractors have been developing a photochemical modeling system and supporting database over the past two years.  The data and knowledge base gained as a key sponsor and contributor to the Central California Ozone Study (CCOS) has been essential to this effort.  Integral contributions have been made by several other entities involved in CCOS, including the CARB and their associated contractors at the National Oceanic and Atmospheric Administration and the University of California at Riverside, as well as the San Joaquin Valley and Sacramento Air Districts and their respective contractors.  Given the plethora of modeling efforts conducted by each of these groups stemming from the CCOS 2000 program, the BAAQMD effort has attempted to bring together the best information and modeling approaches possible.  As a result, the research, modeling, testing, and evaluation conducted in this project has been, and continues to be, a rather complex and highly interactive endeavor.

PURPOSE AND GOALS

The original purpose of the current study was to modernize the District’s modeling capabilities to align with the modeling systems to be evaluated by the CARB under the CCOS program, and to use those systems to develop a new photochemical modeling database to support the 2004 Bay Area SIP revision.  With the elimination of the need to submit a 2004 SIP revision for 1-hour ozone, the objectives of the study have shifted slightly, but the overall focus remains the same.

The purpose for this study is divided into two distinct goals:

Immediate and foremost goal:
Provide the District with a photochemical modeling system and technical analyses consistent with CARB to support future Bay Area SIP submittals, including assessment of projected future year ozone levels in the SFBA, examination of local and regional control strategy effectiveness, and analyses of the impact of those strategies on regional ozone throughout central California.

Longer-range goal:
Provide the District with a modern tool base that they can use to build a modeling “climatology”, consisting of many additional historical episodes with which to evaluate local/regional ozone patterns and issues surrounding inter-basin transport.

Pollution does not respect political boundaries.  There is documented air mass flow from the Bay Area into inland areas of the State, and vice-versa.  The Federal Clean Air Act recognizes such transport and addresses the manner in which up- and down-wind areas are interconnected in the regulatory process.  One of the goals of this study is to provide information that should assist in that regulatory assessment.  In addition to air mass and pollutant flow, there are also mobile source emissions that originate within one area but continue as vehicles move to another area.

Both of these phenomena can be addressed from the photochemical modeling system developed in this study.  Pollutant mass transport can be explicitly addressed because the modeling domain used in this study extends well beyond the SFBA, thus accounting for such air mass movement within the modeling system.  The movement of vehicles can be addressed through the use of complex transportation model output results being used in estimating mobile source emissions.  Such transportation models are used by Metropolitan Transportation Commission (MTC) in the San Francisco area, and Sacramento Association of Governments (SACOG) in the Sacramento area.  Alpine Geophysics has developed a California-wide Integrated Transportation Network that facilitates such analyses.

[Home]