Particulate Pollution and Associated Health Effects
Particulate pollutants are typically a mixture of organic and inorganic air-borne particles that can occur in either the solid or liquid state. The concentration of PM is not uniform in the atmosphere and varies depending on weather, precipitation levels and level of anthropogenic activities.
International studies based on time series data assessment have confirmed the association between elevated levels of particulate air pollution and a decline in lung function or increase in respiratory symptoms such as cough, shortness of breath, wheezing and asthma attacks. While short term exposure to particulate matter (PM) can induce inflammatory reactions in the respiratory and/or cardiovascular system, long term exposure has been seen to have a direct correlation with substantial reduction in life-expectancy. Inhaled PM can also alter the ability of the lungs to handle bacteria thereby leading to enhanced susceptibility to microbial infections.
Bear in mind that the intensity of the health effect of PM is in fact inversely proportional to its size! The smaller the particle, the more lethal it is. Particles in inhaled air are deposited selectively throughout the respiratory tract at locations determined by their size. Particles with an aerodynamic diameter or particle size of 10m (microns) commonly known as coarse particles – are capable of reaching the upper part of our airway and lungs. Sources of PM10 include wind-blown dust from uncovered soil, pollen spores, traffic produced road dust, mining operations amongst others.
Fine particles that have an aerodynamic diameter of 2.5 m are able to penetrate more deeply into the lung, as far as into the alveolar region, making them more dangerous. Extended exposure to PM2.5 has been known to cause severe cardiovascular & respiratory diseases leading to lung cancer in the more extreme cases. 2 common sources of PM2.5 include burning biomass and combustion of fossil fuels. For example, when cars and trucks burn petrol, they release significant amounts of sulphur dioxide which is oxidized in the atmosphere to form sulphuric acid (H2SO4) which in turn reacts with ammonia (NH3) to produce fine ammonium nitrate particles.
Managing PM pollution from the transport sector has in fact been a top priority among many local governments especially in the developing economies that are faced with rising levels of this silent killer. In this regard, the rampant use of diesel especially for commercial vehicles, that tend to have high trip densities, has come under intense fire. A diesel truck emits 100 times the particle mass, per km drive, as compared to a passenger car with a catalytic convertor. Diesel PM is almost pure carbon. Many studies have established that diesel exhaust cause mutations in chromosomes and is capable of damaging the DNA, triggering cancer in the process.
The dynamic nature of these airborne particles as well as the complexity of their structure containing heterogeneous components with diverse chemical & physical properties implies that different characteristics of PM may be relevant to different health effects. Keeping in view the trans-boundary nature of this problem and the associated health effects, the World Health Organization has published air quality guidelines and interim targets for PM (annual mean and 24 hour mean) to allow countries to identify PM pollution hotspots areas within their geographies.
Reference:
– World Health Organization: Air quality guidelines for particulate matter, ozone, nitrogen dioxide and sulfur dioxide – Global update 2005
– U.S Environmental Protection Agency: www.epa.gov
– Clean Air Initiative www.cleanairnet.org
– Asian Development Bank www.adb.org
– Wikipedia www.wikipedia.org
