Amongst air pollutants, inhalable and especially respirable particles from anthropogenic sources cause the greatest concern for public health. Particulate matter is a mixture of solid particles and liquid droplets found in the air, also know as soot. Instances of extreme pollution by fine particles in London in the 1930's, 40's, and 50's killed thousands of people and highlighted the importance of addressing this form of air pollution. It is now understood that even at low concentrations fine particles which are inhaled and become imbedded in the lungs are linked to premature death, chronic bronchitis and aggravated asthma. Children with asthma, the elderly and people with cardiovascular or respiratory disease are especially at risk from fine particle pollution. Governments, in the past, regulated against inhalable particles but now regulate a new standard for smaller, fine particles which travel deeper into the lungs and have been linked to premature deaths, chronic bronchitis and aggravated asthma. A significant measure of fine particles result from the combustion of fuel by power plants and diesel trucks and buses, among others. Lorries and buses are responsible for 55% of particulate and 39% on NOx transport emissions. Particulate matter also reduces visibility.
Health effects from air pollution include the following types of diseases or adverse impacts on specific physiological systems: cancer, cardiovascular or blood toxicity, developmental toxicity, endocrine toxicity, gastrointestinal or liver toxicity, immunotoxicity, kidney toxicity, musculoskeletal toxicity, neurotoxicity, reproductive toxicity, respiratory toxicity, and skin or sense organ toxicity.
Chemicals are identified as "recognized toxicants" based on the hazard identification efforts of authoritative national and international scientific and regulatory agencies. To date, such efforts have been focused on only three types of toxicity: cancer, reproductive toxicity, and developmental toxicity. Chemicals are identified as "suspected toxicants" based on reports in the scientific or regulatory literature, or on information abstracted from major toxicological databases. Suspected toxicants possess evidence that they can cause specific adverse health effects, but no authoritative hazard identification is currently conducted by regulatory agencies or scientific organizations for that health effect.
In 1999 the US Environmental Protection Agency (EPA) is adding new fine particle standards (PM2.5) to the existing PM10 standards. The numbers, 2.5 and 10 refer to the particle size measured in microns. The EPA is adding an annual PM2.5 standard set (Fg/m3) The annual component of the standard was set to provide protection against typical day-to-day exposures as well as longer-term exposures, while the daily component protects against more extreme short-term events. The EPA is retaining the current annual PM10 (Fg/m3) and revising the form of the PM10 24-hour (Fg/m3) standard set at 150.
Studies in the United States and in Europe indicate that potentially the largest damage associated with health may result from fine particulate matter (PM10 and PM2.5). Therefore, effective strategies for balancing efforts to control the different environmental problems and the various pollutants should not leave out the health impacts caused by fine particles.
An area where improvements in particulate pollution can be made is in diesel pollution. Buses and trucks can run much more cleanly on natural gas, rather than generating large amounts of diesel particulates which are often discharged at sidewalk level. Gas-powered trucks and buses do cost more - either to retro-fit existing diesel-powered vehicles or to buy new ones. Operators of urban diesel fleets of all kinds should consider replacing or retrofitting existing fleets of commercial diesel vehicles to run on natural gas.
European Environmen Ministers meeting in Brussels, December 1998, anounced a new Directive aimed at slashing particulate emissions by 90% by 2005. The new agreement will mean that new heavy duty vehicles will cut their emissions of: Particulates by 30% by 2000 and then by a further 80% cut on these standards by 2005, through the use of particulate traps which will remove even the smallest particles, which pose the greatest health risk; Oxides of nitrogen (NOx) by 30% by 2000, and on confirmation of the technical feasibility of state of the art technology to be reviewed in 2002, a further 60% by 2008; and Hydrocarbons and carbon monoxide by 30% by 2000 and a further 30% by 2005.
Data on air quality in Europe indicate that population exposure to sulfur dioxide and lead declined substantially in the early 1990s and that these air pollutants have remained of concern in a limited number of cities in the European region. However, the levels and trends of pollution with respirable particulate matter are still of concern, and the ambient levels of nitrogen dioxide and ozone have not improved. The health effects of common air pollutants occur at various concentration levels, including those considered low. Strategies for reducing exposure must not therefore be limited to eliminating extreme cases of high pollution; instead, they should aim at decreasing average exposure levels among the entire population.