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District Adopts Wood Burning Regulation

Particulate Matter Overview

What is particulate matter

The dangers of PM

PM conditions in the Bay Area

Efforts to reduce PM

What you can do

More information

What Is Particulate Matter (PM)?
Particulate matter (referred to as PM) consists of very small liquid and solid particles suspended in the air, and includes particles smaller than 10 microns in diameter (PM 10 ) as well as finer particles smaller than 2.5 microns in diameter (PM 2.5 ). Particles with a diameter between 2.5 and 10 microns are sometimes referred to as "coarse particles". The following figures illustrate how very small these particles are.

Ambient PM is made up of particles that are emitted directly, such as soot and fugitive dust, as well as secondary particles that are formed in the atmosphere from reactions involving precursor pollutants such as oxides of nitrogen, sulfur oxides, volatile organic compounds, (NOx, SOx, and VOC), and ammonia. Secondary PM and combustion soot tend to be fine particles (PM 2.5 ), whereas fugitive dust is mostly coarse particles.

Directly-emitted particles come from a variety of sources such as cars, trucks, buses, industrial facilities, power plants, construction sites, tilled fields, unpaved roads, stone crushing, and burning of wood.

Other particles are formed indirectly when gases from burning fuels react with sunlight and water vapor. These particles are an indirect product from fuel combustion in motor vehicles, at power plants, and in other industrial processes. Many combustion sources, such as motor vehicles and power plants, both emit PM directly and emit pollutants that form secondary PM. Ammonium Nitrate and Ammonium Sulfate are the principal forms of secondary PM.

The District has conducted an analysis of fine PM in the Bay Area. The study uses ambient PM measurements and emissions data to determine the major PM sources and their approximate contributions to Bay Area PM concentrations. On winter days when the Bay Area experiences peak ambient PM concentrations, the largest single source of PM2.5 is wood burning, followed by ammonium nitrate and motor vehicles. A copy of the report is available here

The dangers of PM
PM causes adverse impacts in terms of public health, visibility, atmospheric deposition, and aesthetic damage. Certain types of PM also contribute to climate change.

Human Health

When we inhale, we breathe in particles that are in the air. The air and the particles travel into our respiratory system (the airway and lungs). The particles can stick to the sides of the airway or travel deeper into the lungs. The deeper particles go, the worse the effect. Smaller particles can penetrate deepest and therefore cause the greatest harm. Particles vary in terms of their size, chemical composition, and source. Some types of PM, such as diesel PM (emissions of particulate matter from diesel engines), are especially harmful.

Health effects can result from both short-term and long-term exposure to PM pollution. Exposure to particulate pollution is linked to increased frequency and severity of asthma attacks and even premature death in people with pre-existing cardiac or respiratory disease. Those most sensitive to particulate pollution include infants and children, the elderly, and persons with heart and lung disease.

Many scientific studies have linked short-term exposure to PM to a series of significant health problems, including:

•  aggravated asthma

•  increases in respiratory symptoms like coughing and difficult or painful breathing

•  chronic bronchitis

•  decreased lung function

•  heart attack

•  premature death

In 1998 the Air Resources Board took action to classify diesel PM as a toxic air contaminant. ARB estimates that diesel PM emissions are responsible for about 70 percent of the total risk from ambient air toxics. Increased incidence of lung cancer is among the risks associated with long-term exposure to diesel PM.

Visibility impairment
PM is the major cause of reduced visibility (haze) in the United States , including both urban and rural areas. PM reduction programs are underway in cities as well as places like the Grand Canyon and the Great Smokey Mountains National Parks where millions of tourists come every year to take in the views.

Atmospheric deposition

The smaller particles are lighter; they stay in the air longer and travel farther. PM 10 particles can remain in the air for minutes or hours while PM 2.5 particles can stay in the air for days or weeks before settling as deposition on surfaces. PM 10 particles can travel as little as a hundred yards or as much as 30 miles. PM 2.5 particles may travel hundreds of miles before settling out. The effects of PM deposition include:

•  making lakes and streams acidic

•  changing the nutrient balance in coastal waters and large river basins

•  depleting the nutrients in soil

•  damaging sensitive forests and farm crops

Aesthetic damage
Certain types of PM, such as soot, can stain and damage stone and other materials, including culturally important objects such as historic buildings, monuments, and statues. Cleaning these landmarks is expensive and time-consuming.

Climate Change

Particulate matter may also play an important role climate change. Some types of PM may heat the atmosphere, while other particles may have a cooling effect, as described below. Climatologists are working to try to better understand the sum of the effects of the varying types of PM on global climate change.

PM containing black carbon (often referred to as “soot”) is created by incomplete combustion of fossil fuels or biomass. Black carbon is a major component of diesel PM, which is a recognized air toxic contaminant, and may have a warming effect on the atmosphere.

According to the Intergovernmental Panel on Climate Change’s (IPCC) Fourth Assessment Report (Climate Change 2007: The Physical Science Basis...), black carbon absorbs solar radiation very effectively, and may contribute to climate change. When black carbon accumulates on snow or sea ice, it may decrease the ability of the surface to reflect sunlight and increase the rate of snowmelt.

The IPCC’s Fourth Assessment Report states that overall, man-made particulates together (but excluding the effect of black carbon on snow or ice) create a net cooling effect. Some of these particulates, such as those containing sulfate, scatter sunlight back to space, thus cooling the atmosphere. Regardless of their impact on the climate, however, man-made particulates are still harmful to human health.

PM conditions in the Bay Area

The Air District currently attains the national air quality annual and 24-hour standards for coarse particulate matter (PM 10 ), and the national air quality annual standard for fine particulate matter (PM 2.5 ). However, the Air District is in nonattainment of the 24-hour standard for PM 2.5. U.S. EPA lowered the 24-hour PM 2.5 standard from 65 µg/m 3 to 35 µg/m 3 in 2006. EPA issued attainment status designations on December 22, 2008, designating the Bay Area as nonattainment for the 35 µg/m 3 PM 2.5 standard. The Air District is required to submit an attainment plan to U.S. EPA within three years of the effective date of the designation that demonstrates attainment of the new national 24-hour PM 2.5 standard within five years of the effective date of the designation. President Obama has ordered a freeze on all pending federal rules; therefore, the effective date of the designation is unknown at this time.

The Bay Area's attainment status is shown below. Currently the Bay Area, like virtually all of California, is classified as nonattainment for the more stringent State PM 10 standard.  The Bay Area, like most urban areas and the Central Valley, is also classified as nonattainment for the State PM 2.5 standard. California’s standards are the most health-protective standards in the nation and are designed to provide additional protection for the most sensitive groups of people. According to ARB, attainment of California 's standards will prevent premature deaths, reduce the incidence of asthma, and avert millions of lost work-days per year.


California Standard
Bay Area Status CA Standard National Standard

Bay Area Status

Nat. Standard

  PM10 - Annual 20 Nonattainment None N/A
  PM10 - 24-hour 50 Nonattainment 150 Attainment
  PM2.5 - Annual 12 Nonattainment 15 Attainment
  PM2.5 - 24-hour None N/A 35 Nonattainment

State and National particulate matter ambient air quality standards. The levels of the standards are expressed in micrograms per cubic meter (µg/m3). Status of Bay Area Region with respect to the State and National particulate matter standards. Based on air monitoring data available as of June 2007.

Efforts to reduce PM

The District implements a number of regulations and programs to reduce PM emissions. These include rules limiting direct PM emissions from open burning of agricultural and non-agricultural waste, controlling dust from earthmoving and construction/demolition operations, limiting emissions from various combustion sources such as cement kilns and furnaces, and reducing PM from activities that generate dust or smoke. In addition, the District also enforces rules that limit indirect PM precursor emissions such as NOx and SO2 from power plants, industrial facilities, and other combustion sources, and volatile organic compounds (VOCs) from petroleum refineries, coatings and solvents, product manufacturing, fuel storage, transfer and dispensing activities, and many other industrial and commercial facilities.

The District is currently working to enhance its efforts to reduce PM emissions from a variety of sources, including charbroilers, and stationary internal combustion engines.

On July 9, 2008, the Bay Area Air Quality Management District Board adopted Regulation 6, Rule 3: Wood-burning Devices to reduce the harmful emissions that come from wood smoke.  Regulation 6, Rule 3 makes it illegal to burn wood or firelogs in household fireplaces and woodstoves when the Air District issues a wintertime Spare the Air health advisory. Regulation 6, Rule 3 also bans the sale and installation of non-EPA-certified wood-burning devices in new construction or re-models, among other stipulations.

Wood-Burning Programs

The District administers programs that deal specifically with emissions from wood-burning appliances such as fireplaces, wood stoves and heaters.  These programs include:

  •  Wintertime Spare the Air alerts that notify Bay Area residents, via email or tex messages, not to burn wood on cold, stagnant winter evenings that create conditions for increased PM levels.
  • The model wood burning ordinance that cities and counties could adopt to further reduce wood smoke impacts in their community.
  •  Financial incentives in specific locations within the Bay Area for residents to remove non-EPA certified wood-burning devices and install EPA certified devices and to replace wood-burning fireplaces with natural gas fireplaces.
  •  The District conducts an annual wintertime survey on the days after a wintertime Spare the Air advisory in order to better understand the public’s attitudes and behavior with respect to wood-burning.

Reducing PM Emissions from Mobile Sources

Motor vehicles are a major source of PM emissions, especially diesel PM which has been classified by the Air Resources Board as a toxic air contaminant.  The Air Resources Board adopted a Diesel Risk Reduction Plan (DRRP) in October 2000. To implement the DRRP, ARB has adopted a series of regulations to require cleaner diesel fuel, to restrict idling of diesel engines, and to reduce emissions from both old and new on-road and off-road diesel engines.

To reduce PM emissions from mobile sources, the Air District implements a variety of incentive programs that help fleet operators offset the cost of purchasing low-emission vehicles, re-powering old polluting heavy duty diesel engines with cleaner, lower-emission engines, and installing emission control devices that reduce particulates and NOx. These incentives are available for a wide variety of on-road and off-road equipment. In addition, one program focuses specifically on school buses. The District also operates a vehicle buy-back program to provide financial incentives to remove the oldest, most polluting light-duty ehicles from our roadways.

SB 656 / PM Implementation Schedule

In 2003 the California Legislature enacted Senate Bill 656 (SB 656, Sher), codified as Health and Safety Code (H&SC) section 39614.  SB 656 seeks to reduce public exposure to PM 10 and PM 2.5 and to make progress toward attainment of State and national PM 10 and PM 2.5 standards. SB 656 required ARB, in consultation with local air quality management districts (air districts), to develop and adopt a list of the most readily available, feasible, and cost-effective control measures that could be used by ARB and air districts to reduce particulate matter. The bill requires the ARB and air districts to adopt implementation schedules for appropriate ARB and air district measures. Finally, no later than January 1, 2009, the ARB must prepare a report describing actions taken to fulfill the requirements of the legislation as well as recommendations for further actions to assist in achieving the State PM standards. The bill requirements sunset on January 1, 2011, unless extended. For more information about SB 656 and to view related documents, see

To comply with SB 656, the Air District reviewed the list of 103 potential PM control measures prepared by the Air Resources Board and developed a Particulate Matter Implementation Schedule which was adopted by the District’s Board of Directors on November 16, 2005.

SB 656 Particulate Matter Implementation Schedule and Response to Comments



Here are a few things individuals, businesses, and other organizations can do immediately to reduce PM emissions and the potential impacts of particulate matter:
  • Reduce motor vehicle use on days with poor air quality.
  • Avoid using your wood stove and fireplace on days that have poor air quality.
  • Avoid using leaf blowers and other dust-producing equipment.
  • Drive slowly on unpaved roads and other dirt surfaces.
  • Get involved with air quality improvement programs in your community.
  • Avoid vigorous outdoor physical activity on days that have poor air quality.
  • If you own or operate an industrial source of PM10, comply with local rules that apply to your operation. Work with local agencies, like the Bay Area Air Quality Management District, to develop strategies that will further reduce PM10 emissions.


For more information about particulate matter, please see these additional websites:
· Information on SB 656
· EPA's PM standard attainment designations for the Western U.S.
· California's PM studies
· California's PM monitoring programs
· General particulate matter information at ARB
· General particulate matter information at EPA
· Health effects of PM
· CARB SB656 factsheet (pdf)
· SB 656 Particulate Matter Implementation Schedule (pdf)
· SB 656 Appendix B Response to Comments (pdf)

Contact: Greg Tholen, Senior Environmental Planner, (415) 749-4954 

Updated August 21, 2008

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