Ambient air monitoring is the systematic, long-term measurement of pollutants in outdoor air to assess local air quality and protect public health.

The Air Monitoring section of the Mojave Desert Air Quality Management District (MDAQMD) is responsible for monitoring ambient (outdoor) air in compliance with the Federal Clean Air Act and California air quality laws.  The California Air Resources Board (CARB) maintains technical information for monitoring stations operated throughout the state, including those within MDAQMD.

Certain pollutants are commonly found in the air and can be harmful to human health when concentrations exceed established levels. In the United States, National Ambient Air Quality Standards (NAAQS) have been established for criteria pollutants, including particulate matter (PM), sulfur dioxide (SO₂), nitrogen dioxide (NO₂), carbon monoxide (CO), ozone (O₃), and lead (Pb).

These standards include both primary and secondary standards. Primary standards are set to protect public health, including sensitive populations such as children, older adults, and individuals with respiratory or cardiovascular conditions.  Secondary standards are designed to protect public welfare, including crops, vegetation, buildings, and visibility. Continuous air monitoring helps determine whether an area is meeting these standards.

MDAQMD operates five air monitoring stations located throughout the District in Barstow, Hesperia, Lucerne Valley, Trona, and Victorville.  These stations collect air quality data 24 hours a day, seven days a week, measuring pollutants such as ozone (O₃), particulate matter (PM₁₀ and PM₂.₅), nitrogen oxides (NOₓ), and hydrogen sulfide (H₂S).  After validation, this data becomes part of the U.S. Environmental Protection Agency’s Air Quality System (AQS), the national air quality database used for regulatory and planning purposes. 

Ambient air monitoring is an essential part of effective air quality management. Monitoring data is used to:

• assess pollution levels;
• provide timely air quality information to the public;
• support implementation of air quality goals and standards;
• evaluate the effectiveness of emission control strategies;
• identify long-term air quality trends;
• support air quality modeling and forecasting; and
• support public health and environmental research.

Monitoring station locations are selected based on population centers, pollution sources, transportation corridors, meteorological conditions, and areas of particular concern such as schools, hospitals, and communities affected by wildfire smoke or windblown dust.  Some stations are also located to measure background air quality away from major emission sources.

Quality assurance systems ensure that monitoring data is accurate, properly recorded, stored, analyzed, and made available to the public.

Particulate Matter (PM₁₀ and PM₂.₅)

Particulate matter (PM) refers to a mixture of solid particles and liquid droplets suspended in the air. These particles vary in size and composition and can come from both natural and human-made sources.

PM₁₀ refers to inhalable particles with an aerodynamic diameter of 10 microns or smaller. For comparison, a human hair is typically about 50 to 100 microns in diameter. Exposure to PM₁₀ can aggravate respiratory illnesses, reduce lung function, and increase the risk of health complications, especially for individuals with existing heart or lung disease.

PM₂.₅ is a subgroup of finer particles with an aerodynamic diameter of 2.5 microns or smaller. Because these particles are much smaller, they can penetrate deep into the lungs and even enter the bloodstream, posing greater health risks. Exposure to PM₂.₅ is associated with more serious health effects, including respiratory and cardiovascular disease, and increased risk of premature death.

Particulate matter may include substances such as carbon, metals, nitrates, sulfates, organic compounds, soil, dust, smoke, and diesel exhaust. Some particles are emitted directly into the air from sources such as construction, unpaved roads, agriculture, and wildfires. Others, known as secondary particles, form in the atmosphere through chemical reactions involving gases such as nitrogen oxides and sulfur dioxide.

PM Program

In addition to monitoring gaseous pollutants, the MDAQMD also monitors particulate matter (PM), which consists of microscopic solid particles and liquid droplets suspended in the lower atmosphere.

Sources of particulate matter include soot, ash, dust, smoke, construction activity, unpaved roads, agriculture, and wildfire events.  Elevated PM levels can affect public health, create haze that reduces visibility, and, in the case of blowing dust or sand, cause property damage from fugitive dust.

Particulate matter is generally classified by particle size. PM₁₀ includes particles with a diameter of 10 microns or smaller, while PM₂.₅ includes finer particles measuring 2.5 microns or smaller.  The smaller the particle, the greater the potential health impact, because finer particles can travel deeper into the lungs and are more likely to affect individuals with asthma, heart disease, and other respiratory or cardiovascular conditions.

Because the Mojave Desert region experiences frequent high wind events and dust-generating conditions, particulate matter monitoring remains an important part of protecting public health and maintaining compliance with state and federal air quality standards.

PM₁₀ and PM₂.₅ Sampling

MDAQMD uses Met One Instruments BAM-1020 monitors to automatically measure and record airborne particulate matter concentrations for PM₁₀ and PM₂.₅.  These instruments use beta attenuation technology to provide continuous, near-real-time measurements of particulate matter in ambient air.

The BAM-1020 works by drawing a measured volume of air through a filter tape, where airborne particles are collected. A small Carbon-14 (C-14) source emits beta particles, which are detected and counted by a sensitive detector.  After the filter collects particulate matter, it is placed between the beta source and the detector. The particles on the filter reduce, or attenuate, the beta particle signal. Attenuation is used to calculate the mass concentration of particulate matter in the air, typically reported in micrograms per cubic meter (µg/m³).

Advancements in monitoring technology have enabled continuous hourly measurement and public reporting of PM levels.  With upgraded instrumentation and support from the California Environmental Protection Agency (CalEPA), MDAQMD can collect and report near-real-time PM₁₀ and PM₂.₅ data to support forecasting, public health notifications, and regulatory compliance.

It's All About the Data

Accurate air quality management depends on reliable data.  Just as weather forecasting relies on continuous meteorological observations, protecting public health from air pollution depends on consistent measurement of atmospheric conditions and pollutant levels.

While the effects of air pollution may not be as immediately visible as severe weather events such as tornadoes or hurricanes, the long-term health impacts can be significant - especially for sensitive populations such as children, older adults, and individuals with respiratory or cardiovascular conditions.

Unlike traditional weather observations, air quality must be measured using specialized instrumentation.  Monitoring equipment continuously collects data on pollutant concentrations, meteorological conditions, and atmospheric movement.  This information is reviewed for accuracy, validated, and submitted to the U.S. Environmental Protection Agency (EPA) for inclusion in national databases used for regulatory planning, research, and public reporting.

Air quality data supports forecasting, public health advisories, exceptional event demonstrations, emissions planning, and atmospheric modeling.  Scientists and air quality specialists use this information to better understand how pollutants move through the atmosphere and how air quality may change over time.

Advancements in technology have enabled near-real-time public reporting.  Reliable instruments, improved communications systems, and online platforms now allow air quality data to be shared quickly and efficiently.  Resources such as EPA’s AirNow provide the public with current conditions, forecasts, and health-based recommendations.

MDAQMD continues to improve data collection and public outreach by supporting near-real-time monitoring, air quality forecasting, and participation in regional ozone mapping and forecasting programs.  As technology advances, access to timely and accurate air quality information helps residents make informed decisions to protect their health.