Clear The Air News Blog Rotating Header Image

July 2nd, 2009:

Frequently Asked Questions on Fine Particles (PM2.5)

Massachusetts Department of Public Health

What is particulate matter?
Particulate matter, which is also known as particle pollution or PM, is a complex mixture of extremely small particles and liquid droplets. Particle pollution is made up of a number of components, including chemicals, metals, and soil or dust particles. The size of the particles is directly related to their potential for causing health problems. Particulate matter is grouped into three size categories: PM10, PM2.5, and ultrafine particles. Particles that are 10 micrometers or less in diameter (PM10) are of the most concern because they can pass through the nose and throat and enter the lungs. Fine particles, also known as PM2.5, are 2.5 micrometers in diameter and smaller. Ultrafine particles are smaller than 100 nanometers. Currently air quality regulations exist for PM10 and PM2.5.

What is PM2.5?
PM2.5 refers to “fine” particulate matter that is 2.5 micrometers in diameter and smaller; in comparison, the average human hair is about 70 micrometers. Particulate matter is primarily the result of fuel combustion or formed from chemical reactions of gaseous pollutants in the atmosphere. Fine particles can be a local pollutant but also are considered regional pollutants because they can be suspended in the atmosphere for long periods of time and transported over long distances. Fine particles are also the major cause of haze or reduced visibility.

Why is PM2.5 an important public health issue?

Why is the Massachusetts Department of Public Health tracking PM2.5 as a public health issue in the state?

Where does PM2.5 come from?

Who is likely to be affected by exposure to PM2.5, and why?

How can I reduce my exposure to PM2.5?

How is attainment of the PM2.5 National Ambient Air Quality Standard (NAAQS) determined using monitoring data?

Are there differences between the calculations for determining NAAQS attainment and the EPHT air quality indicator for PM2.5?

How is the air quality measure (number of days exceeding the daily PM2.5 NAAQS) calculated?

What are limitations of the data?

Where can I get additional information on fine particles?
You can get the above answer on:

Socioeconomic disparities in air pollution-associated mortality

Elsevier Inc. – 26 November 2007


This study aimed to determine whether individuals with lower socioeconomic status (SES) were more susceptible to the acute effects of ambient air pollution than those with higher SES. We included 24,357 Hong Kong Chinese aged 30 or above who died of natural causes in 1998. Information on individual socioeconomic characteristics was obtained by interviewing proxy informants with a standardized questionnaire in all four death registries. Individual SES was indicated by three measures: type of housing, occupational group and education attainment. Poisson regression was performed to assess the short-term effects of ambient air pollution measured by PM10, NO2, SO2 and O3 on mortality for each SES group. The differences in the effects between SES groups were estimated by the interaction between air pollution and SES. We found that PM10 and NO2 were associated with greater risk of mortality on people living in public rental housing than in private housing. The effects of all four pollutants were significantly greater in blue-collar workers than the never-employed and white-collar groups (p<0.05). However, we found no compelling evidence of effect modification by education attainment. Our results provide new evidence on the role of individual’s SES as effect modifiers of the short-term effects of air pollution on mortality. The reduction of risks associated with air pollution for socially disadvantaged populations should be a high priority in public health and environmental policies.

More information on: