Particles                                     

It is now generally accepted that the very small particles emitted by combustion and abrasion have a large effect on annual death rates.  In a typical west European and North American population, a modest 10microgramme /m3 increase in the ambient annual average level of PM2.5 is associated with a 6% increase in death rate.  Built up areas where solid domestic fuel combustion is common can easily raise PM2.5 levels by 20 microgramme per cubic metre. 

References:

Long-Term Exposure to Air Pollution: Effect on Mortality (UK Government report)  
http://www.advisorybodies.doh.gov.uk/comeap/pdfs/finallongtermeffectsmort2009report.pdf
Cardiovascular Disease and Air Pollution.  Committee on the Medical Effects of Air Pollution (COMEAP), Dept of Health , UK , 2005
http://www.advisorybodies.doh.gov.uk/comeap/expertreview.htm

Also, read: 

Health Effects Instiute reanalysis of the six citires and american cancer society analsyis 

Journal of the American Medical Association, Arden Pope III et al   (last accessed Feb '09)

New England Journal of Medicine, January 2009, Arden Pope III et al 

World Health Organisation 2005 report   

The reminder of this page is being updated . . . . .

Particulates

Air has tiny solid particles or fine liquid droplets suspended within it often called particulates. Usual concentrations are invisible but high concentrations can be seen as a haze, a mist or smoke especially when accompanied by condensing water vapour.  The large majority are less than a hundreth of a millimetre across and are known as P M tens (PM₁₀ = particle ten m icrometres = 10µm). The fraction of the PM10's which are thought to be the most poisonous are less than 2.5 micrometres across and are called PM2.5's. The smallest of the particulates are the ultrafine particles which are smaller than 0.1µm across (PM0.1) and often contain less than a million molecules. There are many millions of PM10's suspended in each cubic metre of  even clean air. The chemistry of suspended particulate matter is varied and depends upon the source and can contain carbon, nitrates, sulphates, metals, polycyclic aromatic hydrocarbons to name but a few. When coal or wood is burnt, many of the poisonous emissions start as vapour but quickly condense onto surfaces such as the inside surface of chimney stacks or onto the surfaces of the suspended particles. Particles are the main delivery system for many of the inhalable poisons.

Sources       

Natural as fine dust, salt spray etc.. Anthropogenic (man made) primary particles direct from combustion mainly but other sources include quarrying. Also secondary particles formed in the air due to chemical reaction.
 
Health Effects

PM10's are readily inhalable and because of their small size are not filtered and penetrate deeply into the cardiovascular system where they cause damage. Those smaller than 2.5 um penetrate deeper than those closer to 10um. Mainly because of their physical properties, they have a strong association with most types of respiratory illness and even mortality. They also have a strong association with circulatory (heart disease and strokes) disease and mortality. Particles allow many chemicals harmful to human health to be carried to many of our internal organs causing a wide range of illness and mortality including cancer, especially lung cancer, brain damage and damage to the unborn child. 

A list of health effects compiled by the US EPA who state that elevated particulate concentrations have been associated with:

•   increased total mortality;
•   increased respiratory deaths;
•   increased cardiovascular deaths;
•   increased cancer deaths;
•   increased risk of premature births and infant mortality;
•   increased risk of pneumonia;
•   increased risk of postneonatal mortality from respiratory disease and sudden infant death syndrome;
•   increased hospital admissions and emergency room visits;
•   increased hospital admissions, emergency room visits and surgery for respiratory and cardiovascular conditions;
•   exacerbation of asthma attacks, increased bronchodilator use and increased hospital admissions due to asthma attacks;
•   increased pneumonia, bronchitis and chronic obstructive pulmonary disease;
•   increased respiratory symptoms in both the lower and upper respiratory tract;
•   decreased lung function;
•   increased incidences of rhinitis;
•   increased absenteeism and  increased number of days of restricted activity.
  

Size of Health Effects

Long term exposure has been estimated by the UK government to reduce life expectancy by 3.5 days per microgram/m3 averaged over a whole population. Therefore, if four percent of the population are made ill and killed by a lifetime particle exposure of PM10's and if exposure averages 30µgm^-3 then the loss in life years per affected person would be more than ten. The annual number of deaths would be 24 000. Within this group, there would be a minority with a  larger loss in life years. People living in close proximity to a coal or wood fire would have a higher long term exposure, in some cases much higher.
An American study (Pope et al JAMA March 8 2002 Vol 287, No 9) concluded that cities which had higher PM2.5 levels had a higher mortality rate. (Note: a relative risk of 1.0 means no increase in death rate)

* probably an over estimate: 1.08 and 1.24 are probably better figures.
The comparison with smoking illustrates that although air pollution has a large health effect, it is small compared to tobacco smoking. However, the air pollution figures apply to whole populations not just to those exposed as in cigarette smoking. It is highly probable that within those populations, that those exposed to high pollution levels have a higher mortality rate than those exposed to lower levels.

Short term exposure causes death advancement and hospital admissions mainly but perhaps not exclusively in those frail, very elderly or seriously ill. The UK government have estimated the numbers affected as:

Exposure

General annual averages for UK cities are between 15 and 35 ug/m3 but less for many rural areas. Actual exposures vary and for many people are well above ambient levels. Living in the general vicinity of industrial sites, including quarries and combustion power stations will expose you to higher particle pollution. Also living near roads and in areas of domestic combustion activity will expose you to higher than ambient levels. Environmental tobacco smoke can expose you anywhere between 17 and 5000ug/m3 PM2.5's. Being near to roads often means a concentration of up to 15 µg m ^-3 of PM10's above the local background.  In Christchurch, New Zealand, domestic wood heating is common and summer PM10's level are usually less than 20ug/m3 whilst winter ambient levels often rise above 100ug/m3. Indoor air where a domestic fire is burning can make concentrations exceed 1000ug/m3. Biomass smoke from cooking appliances in the developing world often means women and children being exposed to over 5000ug/m3 for several hours per day and the consequent death rate is high, over 2 million a year.

Ref (4) 
  The quantification of the effects of air pollution on health in the United Kingdom: COMEAP,  Department of Health, UK, 1998,  ISBN 0113221029