Particulate Matter Overview
Is Particulate Matter (PM)?
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.
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.
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
increases in respiratory symptoms like coughing and difficult or painful breathing
decreased lung function
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.
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
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.
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.
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.
The District administers programs that deal specifically with emissions from wood-burning appliances such as fireplaces, wood stoves and heaters. These programs include:
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.
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 www.arb.ca.gov/pm/pmmeasures/pmmeasures.htm.
more information about particulate matter, please see these additional
August 21, 2008
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