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2003 AIR QUALITY ATTAINMENT PLAN
CHAPTER IV – TRANSPORT OF POLLUTANTS

IV.1     INTRODUCTION

This chapter of the attainment plan addresses air pollution transport, identifies transport couples, and discusses transport mitigation regulations related to the Upper Sacramento Valley. Further, a review of amendments to the transport mitigation regulation is provided, and finally, the relevance of the Central California Ozone Study is discussed.

Synopsis

The California Air Resources Board (ARB or Board) has identified that air pollution is transported from the Broader Sacramento Area (BSA) to the Upper Sacramento Valley (USV), (defined in Section IV.2 below), thus establishing the BSA/USV Transport Couple. The impacts of transported BSA air pollution to air districts in the USV are variable. Transport pollution impacts are classified using the terms Inconsequential, Significant, and Overwhelming, as defined in Section IV.2 below. The California Air Resources Board’s (ARB) most recent assessment, published in March 2001, indicates that all three of these classifications occur in the BSA/USV transport couple region with the latest classification of “inconsequential” added to describe the transport couple assessment for Shasta County.

IV.2          DEFINITIONS AND TERMINOLOGY

Air Basin – an area wherein there are similar meteorological and geographic conditions; also defined by political boundaries; an area in which the air mass is homogeneous; an area usually bounded by topographical features.

Ambient Air Quality Standards - specified concentrations and durations of air pollutants which reflect the relationship between the intensity and composition of air pollution to undesirable effects established by the state board or, where applicable, by the federal government

Broader Sacramento Area (BSA) - includes the Sacramento Metropolitan Air Quality Management District; Yolo-Solano Air Pollution Control District; the portions of the El Dorado County Air Pollution Control District included in 1990 U.S. Census Tracts 306.01, 307, 308.01, 308.02, 308.03, 308.04, 309.01, 309.02, 310, 311, 312, 315.01, and 315.02; and the portions of the Placer County Air Pollution Control District included in 1990 U.S. Census Tracts 203, 204, 205, 206.01, 206.02, 206.03, 207.01, 207.02, 207.03, 208, 209, 210.01, 210.02, 211.01, 211.02, 212, 213.01, 213.02, 214, 215.01, 215.02, 216, 218.01, and 218.02; and that area of the Feather River Air Quality Management District which is south of a line connecting the northern border of Yolo County to the southwestern tip of Yuba County, and continuing along the southern Yuba County border to Placer County.

Couple – a pair of geographic areas, one considered upwind and one considered downwind.

Exceedance – any ozone concentration greater than the ambient air quality standard for ozone.

Extreme Concentration – a concentration that is statistically expected to occur less frequently than once every year.

Inconsequential – an ozone transport impact classification describing a condition when upwind emissions were not transported or did not appear to contribute significantly to a violation of the State ozone standard in the downwind area.  A violation not impacted by transported emissions is considered local and results when the wind flow patterns and atmospheric conditions do not strongly suggest responsibility from an upwind area.  The responsibility of “inconsequential” transport lies with the downwind area.

Mitigation – in air pollution control, mitigation refers to those measures that are taken to prevent or reduce emissions in the atmosphere and may include the adoption and enforcement of local air district rules and regulations to regulate emissions from stationary sources, land-use and transportation control measures achieved through the California Environmental Quality Act (CEQA), and the adoption of state and national regulations to reduce emissions through fuel reformulation and new engine technologies.

Model – a computer-based representation of atmospheric processes used, among others, to develop emission inventories, determine dispersion of pollutants, and predict downwind concentrations and impacted areas.

Overwhelming – an ozone transport impact classification describing a condition when the emissions from the upwind area independently results in a violation of the State ozone standard in the downwind area on any given day.  Significant emission sources in the downwind area were not in the pathway of the air parcel that was transported from the upwind area.  The responsibility for a violation caused by “overwhelming” transport lies with the upwind area.

Particulate Matter - any material, except uncombined water, that exists in finely divided form as a liquid or solid at standard conditions.

Precursor - a directly emitted pollutant that, when released to the atmosphere, forms, or contributes to the formation of a secondary pollutant for which an ambient air quality standard has been adopted.

Profiler – equipment that provides continuous winds aloft measurements using the Doppler shift principle and radar waves.

Reactive Organic Gases - any compound containing carbon, except methane, carbon monoxide, carbon dioxide, carbonic acid, metallic carbides or carbonates, ammonium carbonates, and halogenated hydrocarbons.

Significant – an ozone transport impact classification describing a condition in which the emissions from the upwind area contributed measurably to a violation of the State ozone standard in the downwind area on any given day, but did not “overwhelm” the area.  A violation is considered caused by “significant” transport if the emissions from sources within the downwind area combine with the transported parcel carrying ozone or ozone precursors from the upwind area.  A violation classified as “significant” is considered shared, with responsibility lying with both the upwind and downwind areas.

Transport – horizontal movement of air pollution or air pollution precursors at the earth's surface or aloft.  Vertical movement of air pollution is referred to as mixing.

Upper Sacramento Valley (USV) - includes the Colusa, Butte, Glenn, Tehama, and Shasta County Air Pollution Control Districts, and that area of the Feather River Air Quality Management District which is north of a line connecting the northern border of Yolo County to the southwestern tip of Yuba County and continuing along the southern Yuba County border to Placer County.

IV.3     BACKGROUND

The California Clean Air Act (Act) of 1988 requires each air pollution control and air quality management district (district) in which a State ambient air quality standard for ozone, carbon dioxide, sulfur dioxide, or nitrogen dioxide is exceeded to develop a plan and an emission control program to attain the State standard(s).  The Act recognizes that ozone and ozone precursors can be carried (transported) by winds over long distances and thereby contribute to air quality problems outside the district or air basin where they originated. To address this, the Act requires upwind districts to mitigate the impacts on downwind areas of pollutants emitted in the upwind districts (see section 39610 of the Health and Safety Code).  The Act directs the ARB to assess the impacts of such transport and to establish mitigation requirements for upwind districts. 

In terms of identifying transport couples and assessing the downwind impacts the Act directs the ARB to:

1)      Identify downwind areas affected by transported air pollutants and the upwind air basins or regions that are the sources of the pollutants;

2)      Assess the relative contribution of upwind emissions to downwind ozone concentrations as “overwhelming”, “significant”, “inconsequential”, or some combination thereof, to the extent permitted by available data (Health and Safety Code, section 39610(a) and (b)); and

3)      Update this analysis at least once every three years (Health and Safety Code, section 39610(d)).

In terms of transport mitigation the Act requires that:

Districts within the areas of origin of transported air pollutants shall include sufficient emission control measures in their attainment plans for ozone to mitigate the impact of pollution sources within their jurisdictions on ozone concentrations in downwind areas.  At a minimum, the attainment plans for districts within the Broader Sacramento Area shall conform to the following requirements:

1)      require the adoption and implementation of best available retrofit control technology, as defined in Health and Safety Code section 40406, on all existing stationary sources of ozone precursor emissions as expeditiously as practicable.  At a minimum, the plan shall provide for the adoption of rules that represent best available retrofit control technology for source categories that collectively amount to 75 percent of the 1987 actual reactive hydrocarbon emissions inventory for permitted stationary sources, and 75 percent of the 1987 actual nitrogen oxides emissions inventory for permitted stationary sources, no later than January 1, 1994.

2)      include measures sufficient to attain the state ambient air quality standard for ozone by the earliest practicable date within the Upper Sacramento Valley, except as provided in Health and Safety Code section 41503(d), during air pollution episodes which the state board has determined meet the following conditions:

(A)              are likely to produce a violation of the state ozone standard in the Upper Sacramento Valley; and

(B)              are dominated by overwhelming pollutant transport from the Broader Sacramento Area; and

(C)              are not measurably affected by emissions of ozone precursors from sources located within the Upper Sacramento Valley.

IV.4     IDENTIFICATION AND ASSESSMENT OF TRANSPORT COUPLES

More than one assessment, or transport impact classification, may apply to a transport couple.  The assessments rely on, but are not limited to, exceedance values at any given air monitoring station and meteorological data such as wind speed and direction.  As these parameters vary from day to day, the assessments also vary.  Therefore, while there may be a finding of “inconsequential” transport impacts on one or more violation days, other days may be assessed as “overwhelming” and/or “significant”.  Likewise, an area that is the upwind air basin on one day may be the downwind air basin on another day.

IV.5     TRANSPORT MITIGATION

Transport mitigation has a role in California’s efforts to achieve health-based State ambient air quality standards. For ozone, one of California’s most persistent air quality problems, the California Clean Air Act (Act) specifically recognizes that local air pollution control districts need to mitigate the impact of pollutants that they generate and transport downwind. The ARB has the responsibility to assess the relative transport contribution of air districts and to establish mitigation requirements. State law also directs the ARB to take specific actions to reduce air pollutant emissions from mobile sources, fuels, and consumer products. These statewide measures reduce emissions in all air districts in California.

ARB first adopted transport mitigation requirements for air districts in 1990 based on an analysis of transport relationships between districts. The regulations identified transport couples consisting of an upwind area (source of transported emissions) and a corresponding downwind area (receptor of transported emissions). As required by State law, ARB also determined whether the contribution of transported pollutants was overwhelming, significant, inconsequential, or a combination thereof. The impact of transport on most downwind areas was found to be a combination. Also, some districts were found to be both receptors and sources of transport pollutants. The 1990 regulations established mitigation requirements for upwind areas found to have either overwhelming or significant impacts on downwind areas.

Districts have been implementing the primary mitigation requirement – application of BARCT (Best Available Retrofit Control Technology) for the last decade.

IV.6     THE BROADER SACRAMENTO AREA/UPPER SACRAMENTO VALLEY   TRANSPORT COUPLE                                                                                                                                                                                                                                                                             

ARB’s 2001 report represents the third update to the 1990 assessments. The initial transport assessment was approved by the ARB in August 1990. The first triennial update of the ozone transport assessment occurred in August 1993; the second update was completed in November 1996; and the third update was completed in March 2001. The next update is planned for 2004. ARB staff presented the third triennial update and the summary report to their Board at its April 26, 2001, hearing. The Board adopted the proposed changes to the list of identified transport couples. Only subject matter relative to the NSVAB will be discussed in this chapter.

Prior Transport Assessments

Based on prior assessments, the ARB concluded that historically, the Upper Sacramento Valley (USV) was impacted by “overwhelming”, “significant”, and “inconsequential” transport from the Broader Sacramento Area (BSA).  Based on the 1993 and 1996 assessments, transport from the BSA was found to be “overwhelming” at the following air monitoring sites:

    Chico (Butte County)                 Arbuckle (Colusa County)
    Willows (Glenn County)              Redding (Shasta County)
    Yuba City (Sutter County)           Red Bluff (Tehama County)

Based on the 1990 and 1996 assessments, transport was found to be “significant” at the following air monitoring sites:

    Chico (Butte County)                  Colusa and Arbuckle (Colusa County)
    Willows (Glenn County)               Redding and Anderson (Shasta County)
    Yuba City (Sutter County)            Red Bluff (Tehama County).

Based on the 1990 assessment, transport was found to be “inconsequential” at:

    Redding and Anderson (Shasta County).

In the 1996 assessment, it was found that none of the sites had “inconsequential” transport during the period 1994 through 1996 and therefore, the “inconsequential” transport assessment was removed.

Current Transport Assessment

The ARB determined in their March 2001 report that the ozone exceedances on August 4, 1997, August 19, 1998, and September 24, 1998, at Redding in Shasta County had little or no impact from transport of upwind emissions from the Broader Sacramento Area.  Based on these analyses, the ARB staff recommended re-instatement of the classification of “inconsequential” to the USV. “Inconsequential” transport means that little or no transport impacted the monitor and that the exceedance was due to local emissions. At a public hearing on April 26, 2001, the ARB adopted the amendments to the transport identification regulation as proposed by staff.   

Therefore, in addition to the 1996 transport assessments of “significant” and “overwhelmed”, the transport of pollutants from the BSA was found to be “inconsequential” on the above-referenced dates as measured at the monitoring site at Redding in Shasta County.  The ARB’s findings indicate that Shasta County, as well as the neighboring counties, has a responsibility to reduce emissions to attain the State ozone standard in the USV.

This serves to illustrate that emissions in the Upper Sacramento Valley can, on occasion, cause exceedances of the State ozone standard without a transport component.

IV.7     AMENDMENTS TO THE OZONE TRANSPORT MITIGATION REGULATIONS

At a public hearing on April 26, 2001, the ARB Board of Directors directed ARB staff to initiate a review of the transport mitigation requirements and return with recommendations. One question the Board raised was whether upwind district’s rules are as stringent as those of their downwind neighbors. Another issue was whether upwind areas will continue to meet their mitigation responsibilities, once they have reached California's ozone standard within their own jurisdiction. Currently, nonattainment upwind districts are implementing “all feasible measures” to attain the State ozone standard in their own districts in lieu of complying with a five percent annual reduction in emissions of ozone precursors (H&SC Section 40914). This is reflected in the air quality plans adopted by air districts and approved by ARB. However, there was no mechanism that would require upwind districts to pursue all feasible measures to mitigate transport impacts as they approach or attain the ozone standard in their own districts.

The Board’s direction to revisit the transport mitigation regulations has resulted in the development of new regulatory amendments. One of the new amendments that we will focus on in this chapter involves strengthening the definition and implementation of all feasible measures.

All Feasible Measures

H&SC Section 40914 requires each district that is nonattainment for the State ozone standard to develop and implement an ozone attainment plan. This plan is to include measures that will achieve at least a five-percent annual reduction in district-wide emissions for ozone precursors. If the district cannot achieve the five- percent reduction, and the ARB concurs, the attainment plan may be approved if it includes all feasible measures. The goal is to achieve and maintain the State ozone standard by the earliest practical date.

The implementation of all feasible measures has been the primary mechanism through which districts have achieved the local emission reductions needed to maintain steady progress towards attaining the ozone standard in their own district. Districts prioritize the adoption of rules, based on technical feasibility, economic considerations, and air quality benefits for their district.

The focus of all feasible measures under the Act is on attaining the standard within each district. It does not address the issue of emission reductions needed to mitigate transport impacts or establish a process by which the upwind and downwind districts work together to address emissions under their respective jurisdictions. Some downwind districts have indicated that a mechanism is needed to ensure continued implementation of all feasible measures as upwind districts get close to attaining the ozone standard. Some downwind districts are also concerned that upwind districts may have less stringent rules or lack rules for similar source categories. This creates a perception of inequality, and does not appear to support the concept of a shared responsibility.

ARB’s recommendations are intended to establish a framework by which upwind and downwind districts work together to ensure the implementation of the most effective measures to mitigate transport as expeditiously as possible. The new amendments add a requirement for upwind districts to implement all feasible measures for transport purposes in addition to their own attainment goals, and to institute a timelier implementation process than currently required under State law. Staff also added definitions to clarify the intent and scope of the "all feasible measures" requirements.

The amendments to the Ozone Transport Mitigation Regulations (Title 17, California Code of Regulations, Subchapter 1.5, Article 6, Section 70600 and 70601) were adopted by the ARB Board of Directors on May 22, 2003. These amendments are discussed in greater detail below.

Requirements

ARB incorporated into the transport mitigation regulations a requirement that all feasible measures must be adopted by the upwind district as expeditiously as practicable. The expeditious adoption of all feasible measures is the approach that the districts are taking to comply with the Act. However, adding this requirement to the transport mitigation regulations achieves three objectives. First, it ensures that upwind districts continue to adopt all feasible measures regardless of their ozone attainment status as long as they continue to have a significant or overwhelming transport impact.  Second, it will result in upwind districts taking into account the needs of the downwind districts when prioritizing their rule adoption schedule. Finally, it will support the concept of shared responsibility for air pollution by ensuring that the upwind and downwind districts work together to mitigate emissions under their jurisdiction. This requirement is intended to ensure that affected upwind and downwind districts consult during development of their respective attainment plans to coordinate effective strategies and control measures.

All Feasible Measures Defined

The amendments include a definition of all feasible measures and ozone precursors. The definition of all feasible measures incorporates the definition used in practice by districts and the ARB since the early 1990s. This definition supports the concept that all feasible measures for transport mitigation will continue to be developed and adopted consistent with current implementation of the concept under the Act. That is, in identifying all feasible measures, the districts will continue to take into consideration the same factors they have used in the past when prioritizing rules for adoption. The definition of "ozone precursors" has also be added to the regulation to clarify that the scope of all feasible measures includes both oxides of nitrogen (NOx) and reactive organic gases (ROG) as ozone precursors.

The definitions are as follows:

·        "all feasible measures" means air pollution control measures, including but not limited to emissions standards and limitations, applicable to all air pollution source categories under a district's authority that are based on the maximum degree of reductions achievable for emissions of ozone precursors, taking into account technological, social, environmental, energy and economic factors, including cost-effectiveness.

·        “ozone precursors” means oxides of nitrogen and reactive organic gases.

Amendments to the BSA/USV Transport Couple

ARB’s amended regulation approved by their Board on May 22, 2003, mandates some significant emission reduction requirements on the BSA, including:

1.                  require the adoption and implementation of all feasible measures as expeditiously as practicable.

2.                  require the adoption and implementation of best available retrofit control technology, as defined in Health and Safety Code section 40406, on all existing stationary sources of ozone precursors as expeditiously as practicable.

3.                  require the implementation, by December 31, 2004, of a stationary source permitting program designed to achieve no-net-increase in the emissions of ozone precursors from new or modified stationary sources that emit or have the potential to emit 10 tons or greater per year of an ozone precursor. 

4.                  include measures sufficient to attain the State ambient air quality standard for ozone by the earliest practicable date within the Upper Sacramento Valley and that portion of the Mountain Counties Air Basin north of the Calaveras-Tuolumne County border and south of the Sierra-Plumas County border, except as provided in Health and Safety Code section 41503(d), during air pollution episodes which the state board has determined meet the following conditions:

a.       are likely to produce a violation of the state ozone standard in the Upper Sacramento Valley or that portion of the Mountain Counties Air Basin north of the Calaveras-Tuolumne County border and south of the Sierra-Plumas County border; and

b.      are dominated by overwhelming pollutant transport from the BSA; and

c.       are not measurably affected by emissions of ozone precursors from sources located within the Upper Sacramento Valley or that portion of the Mountain Counties Air Basin north of the Calaveras-Tuolumne County border and south of the Sierra-Plumas County border.

Implementation of these requirements will be through the BSA districts attainment plans.

IV.8     The Central California Ozone Study (CCOS)

As a result of the transport assessments performed over the last decade by way of the aforementioned transport regulations and, more recently, the California Ozone Studies, air quality professionals have developed a basic understanding of the fundamental transport relationships between the various upwind and downwind regions of California.

The California Ozone Studies include the 2000 Central California Ozone Study (CCOS), which extends from Redding in the north to the Mojave Desert in the south, and from the Pacific Ocean in the west to the Sierra Nevada Mountains in the east, and the 1997 Southern California Ozone Study (SCOS).

These studies will be very valuable in updating transport assessments and preparing future clean air plans.  The California Air Resources Board (CARB) and air districts plan to use the results of the CCOS to prepare the demonstration of attainment for the ozone standard for nonattainment areas in central California. The “data gathering” component of the CCOS was conducted during the summer of 2000. Emission inventory development, data analysis and modeling are on-going projects; the entire effort is expected to be completed by 2005.

One goal of the CCOS project is to develop modeled attainment demonstrations required for federal ozone air quality plans. The modeling will also be useful to further refine our understanding of transport relationships in California during selected ozone episodes. ARB staff is working with all the stakeholders to identify approaches for better assessing transport impacts using the study results. These analyses will be included in the 2003-4 SIP development process for districts in the CCOS domain – including the San Francisco Bay Area, San Joaquin Valley, and Sacramento region. A number of CCOS projects are being fast-tracked in order to provide results that can be used in developing attainment demonstrations for these districts. As a part of these analyses, the impact of upwind control strategies on downwind ozone formation will be evaluated.