Description
The term “particulate matter” (PM) includes both solid particles and liquid droplets found in air. Many manmade and natural sources emit PM directly or emit other pollutants that react in the atmosphere to form PM. Particles less than 10 micrometers in diameter tend to pose the greatest health concern because they can be inhaled into and accumulate in the respiratory system. Particles less than 2.5 micrometers in diameter are referred to as “fine” particles and are responsible for many visibility degradations such as the “Valley Brown Cloud” in Phoenix (see https://www.phoenixvis.net/). Particles with diameters between 2.5 and 10 micrometers are referred to as “coarse”.

Sources
Fine (PM_2.5)= All types of combustion (motor vehicles, power plants, wood burning, etc.) and some industrial processes.
Coarse = crushing or grinding operations and dust from paved or unpaved roads.

Potential health impacts
PM can increase susceptibility to respiratory infections and can aggravate existing respiratory diseases, such as asthma and chronic bronchitis.

Units of measurement
Micrograms per cubic meter (µg/m³).

Averaging interval
Hourly.

National Ambient Air Quality Standards (NAAQS)
For PM₁₀, 150 µg/m³ for a 24-hour average; for PM_2.5, 35 µg/m³ for a 24-hour average.

Number of Monitors
ADEQ operates a limited EBAM monitor network throughout parts of northern and eastern Arizona. The equipment, maintenance, and operational costs of running the network limit ADEQ to the number of semi-permanent monitors that can be used. A very limited number of additional temporary EBAM monitors are maintained by ADEQ and the Forest Service to be used for special studies, wildfire smoke monitoring, and monitoring related to large prescribed burns.

Placement of Monitors
Monitor locations are chosen based on numerous considerations including the locations of smoke sensitive communities, the frequency of proximate prescribed burns, terrain/drainage areas, any past smoke issues, and various monitor siting and maintenance concerns. The locations of the monitors in the network are temporary and monitors may be moved or their use discontinued in the future as conditions warrant.

What These Monitors are Measuring
In the past, the EBAM monitors were set to measure PM₁₀. This means that they measured for particulates 10 micrometers in diameter and smaller. Due in part to the Wallow wildfire in the summer of 2011, some of the monitors were adjusted to measure for PM_2.5, which is more focused on the smaller particulates related to smoke. In August, 2011, the remaining PM₁₀ monitors in the network were switched over to PM_2.5. While the monitors can still pick up on windblown dust events and other sources of particulates, they are now more geared towards collecting smoke data involving particulates 2.5 micrometers in diameter and smaller. For additional information about particulates and their health impacts, visit the following website: https://www.epa.gov/air/particlepollution/.

Changes to the Color Coding of Graphs
Due to confusion in the public regarding the hourly color coding of graphs, several changes were made to the particulate monitor website. Hourly values in graphs had previously been color coded based off of the EPA 24-hour National Ambient Air Quality Standards (NAAQS). Trying to apply a 24-hour standard to an hourly value was confusing and led some members of the public to believe that their air quality was unhealthy when in fact, based off of national standards, it was not. Both hourly and 24-hour average PM_2.5 values are now listed on the website with two different scales provided for converting the values to categorical air quality values. The 24-hour average values can be compared with the 24-hour NAAQS scaling, while hourly values can now be more appropriately compared to a 1-hour index of PM_2.5 values used by public health officials.

Understanding the AQI
The purpose of the AQI is to help you understand what local air quality means to your health. To make it easier to understand, the AQI is divided into six categories:

Each category corresponds to a different level of health concern. The six levels of health concern and what they mean are:

• "Good" The AQI value for your community is between 0 and 50. Air quality is considered satisfactory, and air pollution poses little or no risk.
• "Moderate" The AQI for your community is between 51 and 100. Air quality is acceptable; however, for some pollutants there may be a moderate health concern for a very small number of people. For example, people who are unusually sensitive to ozone may experience respiratory symptoms.
• "Unhealthy for Sensitive Groups" When AQI values are between 101 and 150, members of sensitive groups may experience health effects. This means they are likely to be affected at lower levels than the general public. For example, people with lung disease are at greater risk from exposure to ozone, while people with either lung disease or heart disease are at greater risk from exposure to particle pollution. The general public is not likely to be affected when the AQI is in this range.
• "Unhealthy" Everyone may begin to experience health effects when AQI values are between 151 and 200. Members of sensitive groups may experience more serious health effects.
• "Very Unhealthy" AQI values between 201 and 300 trigger a health alert, meaning everyone may experience more serious health effects.
• "Hazardous" AQI values over 300 trigger health warnings of emergency conditions. The entire population is more likely to be affected.