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Even for healthy people, polluted air can cause respiratory irritation or breathing difficulties during exercising or outdoor activities. How you are affected depends on your current health, the pollutant type and its concentration, and the length of your exposure to polluted air. In order to help keep yourself and others healthy please report pollution complaints.

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  • Phil Martien
  • Air Quality Engineering Manager, Planning and Research
  • 415 749-4660


Planning Rules And Research

415 749-4995

CARE Program

415 749-4660

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CARE Program

The Community Air Risk Evaluation (CARE) program was initiated in 2004 to evaluate and reduce health risks associated with exposures to outdoor toxic air contaminants (TACs) in the Bay Area. The program examines TAC emissions from point sources, area sources and on-road and off-road mobile sources co-located with sensitive populations to help focus mitigation strategies. The main objectives of the program are to:
  • Characterize and evaluate potential cancer and non-cancer health risks associated with exposure to TACs from both stationary and mobile sources throughout the Bay Area.
  • Assess potential exposures to sensitive receptors including children, senior citizens, and people with respiratory illnesses.
  • Identify significant sources of TAC emissions and prioritize use of resources to reduce TACs in the most highly impacted areas (i.e., priority communities).
  • Develop and implement mitigation measures - such as grants, guidelines, or regulations - to achieve cleaner air for the public and the environment, focusing initially on priority communities.

Starting in 2009, the CARE program began also evaluating exposures to fine particulate matter (PM) and helping to craft mitigations to reduce these exposures to address the growing evidence that exposure to fine particles has serious health effects.

How will the District achieve these objectives?

The CARE program is an on-going program that encourages community involvement and input. The technical analysis portion of the CARE program is being implemented in three phases that includes an assessment of the sources of TAC and PM emissions, modeling and measurement programs to estimate concentrations of TAC and PM, and an assessment of exposures, health risks, and effective mitigations. Throughout the program, information derived from the technical analyses is used to focus emission reduction measures in areas with high pollutant exposures and high density of sensitive populations.

To assist the District in guiding this program, CARE Task Force members that include representatives from the community groups, business, local governments, health departments, and research institutions meet on an as-needed basis to receive updates, discuss and review recent findings, and provide input on the program direction. Agendas and presentations from past Task Force meetings are available.

In addition to the Task Force, a Cumulative Impacts Working Group consisting of representatives from community groups, business, government, and non-profit organizations were formed in 2009 to discuss potential revisions to the District's Regulation 2, Rule 5: New Source Review of Toxics Air Contaminants and the California Environmental Quality Act (CEQA) Guidelines to ensure adequate health protection and to evaluate cumulative impacts associated with exposure from multiple sources.  The Working Group held focused meetings to discuss possible approaches for reducing cumulative impacts from stationary sources through new or modified regulations. With the successful adoption of amendments to Regulation 2, Rule 5 and updated Significance Thresholds under CEQA, the Cumulative Workgroup members were invited to join the Task Force and continue their strong commitment in guiding and advising the District's CARE activities.  

Phase I and II: Emissions and Modeling

In Phase I, the District developed a gridded emissions inventory of TAC for year 2005 on a one kilometer by one kilometer grid system for the entire Bay Area.  TAC emissions included more than 90 gaseous and particulate compounds from stationary sources such as power plants, refineries, back-up generators, gas stations, and dry cleaners, as well as both on-road and off-road mobile sources such as cars, trucks, construction equipment, locomotives, ships, and aircraft.  Additional detailed description of how the data were processed is provided in reports entitled "Preparation of Emission Inventories of Toxic Air Contaminants for the Bay Area" (dated August 9, 2006) and "Final Documentation of the Preparation of Year - 2005 Emission Inventories of Toxic Air Contaminants for the San Francisco Bay Area" (dated February 15, 2008).

The results of the Phase I analysis indicate that diesel particulate matter (diesel PM) accounts for over 80% of the cancer risk weighted TAC emissions (Figure 1a) and that on-road and off-road mobile sources are responsible for the majority of cancer risk from air toxics (Figure 1b).  The California Air Resources Board (CARB) identified diesel PM as a toxic air contaminant based on its potential to cause cancer and other health problems, including respiratory illnesses, and increased risk of heart disease and even premature death.  Exposure to diesel PM is a health hazard, particularly to children and elderly. Diesel PM consists of fine particles (soot) that are produced from the combustion of diesel fuel from on-road and off-road diesel-powered equipment, such as diesel trucks, construction equipment, locomotives, and ships.  More details on the findings from the Phase I analysis are presented in the Phase I Findings and Recommendations

   Cancer Risk By Pollutant                       

Figure 1a. Cancer Risk Weighted Emissions by Pollutant   


Cancer Risk By Source

Figure 1b. Cancer Risk Weighted Emissions by Source Type

In Phase II of the CARE program, the District performed regional-scale modeling to determine significant sources of diesel PM and TAC emissions locally and identified areas that have disproportionally higher emissions and concentrations of TACs.  The District applied a regional air quality model using the 2005 emission inventory data to estimate excess cancer risk from ambient concentrations.  The modeling yielded estimates of annual concentrations of five compounds that collectively contributed more than 90 percent of the potential cancer risk from TAC emissions: diesel particulate matter, 1,3-butadiene, benzene, formaldehyde, and acetaldehyde.  The concentrations for each compound were multiplied by the corresponding unit cancer risk factor for the compound, as established by the State's Office of Environmental Health Hazard Assessment (OEHHA) to estimate excess cancer risk per million people by grid cell.  Figure 2a shows the cancer risk weighted emissions data while Figure 2b presents the modeled air toxic risks for 2005.

 CARE 2005 Cancer Emissions                                                            

 Figure 2a. Cancer Risk-Weighted Emissions for 2005       

Modeled 1 km Risk for 2005Legend for Modeled 1 km Risk for 2005

Figure 2b.  Modeled Air Toxic Risk for 2005

Impacted Communities

The District used data on TAC emissions and risk to identify impacted communities.  The impacted communities are areas where the District focuses policies and programs to reduce TAC emissions and exposures.  The emissions and concentrations data were combined with locations of sensitive populations and income levels to identify the impacted communities.  Sensitive populations from the 2000 U.S. Census database (see Figure 3) were identified as youths (under 18 years of age) and seniors (over 64 years of age) and were mapped to the same one kilometer grid used for the toxics modeling.  Block-groups from the U.S. Census database were mapped if over 40% of the population in that block group had income below 185% of the federal poverty level (FPL) (see Figure 4).

 Population Under 182                                                                  

Figure 3.  Population Under the Age of 18

Low Income Population

Figure 4.  Population with Income Levels Below the Federal Poverty Level

The highest cancer risk levels from ambient TAC in the Bay Area tend to occur in the core urban areas, along major roadways and adjacent to freeways and port activity.  The District designated areas as being impacted based on the combination of having the highest emission sources, high pollutant concentrations, and high density of sensitive populations (seniors, children, and low income).  Area boundaries were based on major roadways and natural features, such as the coastline.  The CARE program has identified six impacted communities in the Bay Area including Concord, eastern San Francisco, western Alameda County, Redwood City/East Palo Alto, Richmond/San Pablo, and San Jose (see Figure 5).  More details regarding how the impacted communities were determined can be found at the District's Applied Method for Developing Polygon Boundaries for CARE Impacted Communities, dated December 2009.

 2009 Impacted Communities

Figure 5. CARE Impacted Communities

Monitoring and Measurement Studies

The District has partnered with local community groups and governmental agencies to conduct or assist in local monitoring and measurement studies.

West Oakland Health Risk Assessment

In an example of local-scale modeling, the District partnered with the California Air Resources Board, Port of Oakland, and the Union Pacific Railroad to estimate the health risks from diesel exhaust in West Oakland.  The modeling included emissions from sources at the Port of Oakland, the Union Pacific Railyard, and freeways and other sources in the adjacent West Oakland community.  Draft results of the comprehensive Health Risk Assessment (HRA) were made available in March 2008 and take into account emissions generated from:


  • Diesel trucks and buses                                                           
  • Locomotives (cargo and passenger trains)
  • Ships (cargo and cruise)
  • Harbor craft (e.g., tugs, ferries, fishing vessels)
  • Construction equipment
  • Cargo handling equipment
  • Stationary sources
  • Other significant sources of diesel PM

The study determined that the West Oakland community is exposed to diesel PM ambient concentrations that are almost three times higher than the average background diesel PM in the Bay Area. The estimated lifetime potential cancer risk for residents of West Oakland from exposure to diesel PM is about 1,200 excess cancers per million over a 70 year lifespan. On-road heavy-duty trucks are the largest contributor to the overall potential cancer risk levels in the West Oakland community, followed by ships, harbor craft, locomotives, and cargo handling equipment. The final report, fact sheet, and most appendices are available online. 

West Oakland Truck Survey

The health risk assessment showed that residents of West Oakland are exposed to unhealthful levels of diesel PM.  The District has undertaken several studies to reduce the uncertainties in the truck estimates in the health risk assessment and enhance the District's understanding of air pollution throughout the West Oakland community in order to implement the most effective mitigation strategies.

The District partnered with Pacific Institute, West Oakland Environmental Indicators Project, Sonoma Technologies, Inc., and Wiltec to conduct a comprehensive traffic count survey. The objective of the study was to improve the spatial representation of roadway emissions, identify locations and time of idling trucks, and determine the percentage of Port related trucks versus non-Port trucks.  Community members counted trucks at over 36 intersections in West Oakland over a two week period and additional video footage and counts were conducted on I-880, I-580, and I-980 freeways in 2008-2009.  The results indicate that there are significantly fewer trucks on surface streets than assumed in the HRA, but a higher percentage of Port related trucks.  The survey also found fewer trucks traveling along I-980 and I-580 freeways, but higher number of both Port and non-Port trucks along I-880 compared to the HRA assumptions.  The estimated truck traffic along major routes in West Oakland based on the survey are shown in Figure 6.  The results from the West Oakland Truck Survey are available online. 

 Weekday Truck Traffic in West Oakland

Figure 6. Weekday Truck Traffic in West Oakland

West Oakland Measurement Study

The District partnered with Desert Research Institute (DRI) to conduct the West Oakland Monitoring Study (WOMS). The purpose of the study was to collect supplemental air quality monitoring data to evaluate and validate the local-scale dispersion modeling of diesel PM and TACs for areas within and around the Port of Oakland. Additionally, the supplemental monitoring data will be used to characterize pollutant levels in emission hotspots that modeling may not accurately represent. The WOMS was conducted during two seasonal periods of four consecutive weeks in summer 2009 (July-August) and winter 2009/10 (December-January). The West Oakland Monitoring Study includes time-integrated sampling of particulate matter less than 2.5 microns in diameter (PM2.5) mass, organic carbon (OC) and elemental carbon (EC), selected volatile air toxics and related air pollutants (nitrogen oxides (NO) and sulfur dioxide (SO2)) at fixed sampling locations to determine seasonal 24-hour average concentrations, mobile sampling with continuous monitors to determine spatial variations in pollutant concentration relative to emission sources, and collection and analysis of PM samples for chemical speciation and estimates of source contributions of diesel particulate matter and other combustion sources.  Figure 7 shows an example of real time PM measurements collected using the mobile sampling van. These measurements and modeling results will be used by the District to assess population exposures to TAC and associated health risks in the Bay Area. A report on the findings and appendices are presented in "West Oakland Monitoring Study" and Appendices (October 7, 2010). 

 PA Measurements in West Oakland

Figure 7.  Example of Particulate Matter Reading in West Oakland

Mobile Van Monitoring

Look for the District in your community. The District has a mobile sampling van that is being used to collect real time air quality measurements in the Bay Area from temporary events, ambient conditions, and long term construction projects. The van will also be used to assess local air quality and compare it to the District's existing toxic air monitoring network.

Mitigation Strategy

As noted, diesel PM is the most important toxic air pollutant for most of the Bay Area. CARB has adopted numerous regulations to reduce diesel PM emissions. These rules have already reduced cancer and non-cancer risks in West Oakland and other communities affected by diesel PM and will continue to reduce risks in the future.  Even with the adoption of CARB's regulations, the District is committed to further reducing diesel PM in the Bay Area beyond those measures prescribed by CARB. To achieve this objective, the District developed a comprehensive Clean Air Communities Initiative (CACI) that is a multi-faceted approach that utilizes all of the District’s available resources (see Figure 8). The objective of the program is focus risk reduction efforts in the impacted communities (see Figure 5) and to minimize the effects of land use and transportation decisions on cumulative impacts.


Figure 8.  Clean Air Communities Initiative

The program calls for:

  • Conducting outreach within these communities to receive feedback on how best to address and reduce TAC emissions. The District welcomes community participating in Task Force meetings, community meetings, and resource teams. Please visit Task Force Meeting Agendas to hear about upcoming meetings and review agendas and presentations from past meetings.  Visit the District's Community Outreach webpage for more information on District outreach activities.
  • Allocating grants and incentives in the priority communities to achieve the greatest emission reductions from mobile sources and encourage innovative greenhouse gas reduction efforts to improve air quality for the entire Bay Area. In 2009, the District initiated the Community Grant Fund that provided over $250,000 to actively engage and inform the community on ways of reducing air pollution and improving their health. Mobile grant programs include Carl Moyer Program, I-Bond/Goods Movement Bond, TFCA Regional Fund, and TFCA County Program Managers Fund.  Funds from these programs are focused on entities that operate in these priority communities in order to replace and retrofit heavy duty diesel engines with cleaner burning engines. In 2008, the District awarded $3 million in Climate Protection Grants to Bay Area local governments and nonprofits for implementation of innovative projects to reduce greenhouse gas emissions.
  • Developing rules and regulations that would require reduction of TAC emissions from significant sources. The District’s Board of Director adopted amendments in 2010 to Regulation 2, Rule 5: New Source Review of Toxic Air Contaminants that require all risk assessments of new and modified sources of TACs to use age-sensitivity factors that account for the increased susceptibility of infants and children to exposure to carcinogenic compounds.  The District also develops source-specific regulations to reduce emissions from certain industries.  For example, the District is currently developing rules for metal melting and processing and cement manufacturing. 
  • Completing CEQA Guidelines that provides methodologies for evaluating and reducing air quality and public health impacts from projects and plans in the San Francisco Bay Area. The guidelines address a broad range of health and nuisance related effects caused by criteria pollutants, air toxics, odors, and greenhouse gas emissions and provide updated significance thresholds, assessment methodologies, and mitigation strategies for assessing these impacts.  The CEQA Guidelines specifically address localized air pollution exposures that may occur when housing, schools, and other sensitive receptors are located close to sources of air pollution.  As part of the resource tools that support the CEQA guidance, the District provides technical information and assistance to help cities and counties to assess health impacts from and to new development projects, determine if mitigation is required, identify possible mitigation measures, assess the effectiveness of the measure, and assist with local general plans. 
  • Encouraging local jurisdictions to develop Community Risk Reduction Plans (CRRPs) as a proactive approach that is tailored to each community to achieve the greatest reductions in emissions and exposure to TACs and particulates. The District is committed to communicating and assisting local jurisdictions that chose to develop CRRPs by providing technical expertise in developing emission inventories, modeling assistance, and monitoring. The District is colloborating with San Francisco and San Jose in developing pilot CRRPs.   
  • Partnering with local governments and health departments by providing specific information on the sources and emissions of TAC in their area as well as participating in discussion on in-fill developments and land use decisions. 
  • Completing the first multi-pollutant Clean Air Plan that integrates emission reduction measures for ground-level ozone, particulate matter, air toxics, and greenhouse gases.  The Plan identifies numerous measures to reduce emissions in impacted communities.  
  • Ensuring compliance with existing regulations and permit conditions and developing enforcement agreements for CARB diesel regulations. The District has a well trained staff of inspectors that conduct inspections of air pollution sources, verify compliance, investigate breakdowns, document violations, and respond to citizen complaints about air pollution and accidental releases of air contaminants. In addition, inspectors check recipients of grants to ensure that emission control devices are installed properly. 
  • Monitoring TAC concentrations at both the existing routine monitoring network and at special-study sites. The District operates 27 monitoring networks in the Bay Area that provide data on TAC concentrations. The District also performs short term monitoring studies using portable sampling trailers to evaluate local impacts from high emission sources. For example, the District has conducted or assisted in local monitoring studies in West Oakland, Berkeley, San Francisco, and Cupertino. 
  • Conducting regional modeling of TAC concentrations for past, current, and future years. Diesel was responsible for over 80% of the overall cancer risk based on the 2005 inventory; however, with the adoption of CARB’s diesel regulations, diesel emissions will dramatically decline in the coming years. To see the impact the regulations will have on the Bay Area, the District will be modeling emissions for years 2015 and 2020 to see how emissions changes will change regional risk levels.

Phase III

In Phase III, the District is conducting detailed localized assessments of air pollution emissions and population exposure.  These assessments identify localized areas where exposure to TACs and PM is greatest and the sources contributing most to these impacts.  These studies help refine and target the District's mitigation strategies, and also support mitigation strategies implemented by others, including state agencies and cities and counties.  For example, the District will continue to support and assist local jurisdictions preparing Community Risk Reduction Plans and other plans and programs to reduce local exposure to TAC and fine PM.


Last Updated: 9/29/2014