Air Quality Monitoring
Ozone, carbon monoxide, nitrogen dioxide, particulate matter, sulfur dioxide, and lead; these chemicals, called criteria pollutants, are harmful to our health, materials, and agriculture.
That's why the District's Monitoring Division technicians, chemists, and meteorologists continuously maintain and operate the sophisticated gaseous pollutant analyzers, particle collectors, and weather sensors at monitoring stations in Ventura, Piru, Simi Valley, Thousand Oaks, El Rio, and Ojai to determine the type and level of pollutants in the outside air. These monitoring stations also measure relative humidity, ultraviolet and solar radiation, barometric pressure, visibility, surface temperature, winds, and precipitation. Click here to obtain site information for each monitoring station in Ventura County. You will also be able to view real-time ozone and fine particulate levels recorded at each station.
Because weather conditions are crucial to the formation and movement of air pollution, each monitoring station also measures atmospheric conditions. A seventh monitoring station, called an "atmospheric profiler", measures, in three dimensions, temperatures, wind direction, and wind speed up to 6,000 feet above the surface.
Our quality assurance program ensures valid and
representative air pollution and weather data from each
monitoring station. Ventura County’s historical summaries of
pollutant data and air quality trends can be obtained by
Additional air quality data analysis is available from the
District upon request. Air quality data for the entire state
can be found at the California Air Resources Board’s Air
You can access daily air quality, weather, and agricultural burning reports and forecasts on this website under Air Quality Forecast. Local newspapers also publish daily air quality forecasts using the "Air Quality Index" (AQI). More information about the AQI is available on this website under Air Quality/Air Quality Index. Air quality conditions are listed as "Good", "Moderate", "Unhealthy for Sensitive Groups", "Unhealthy" (for all), and "Very Unhealthy". In recent years, Ventura County's worst air quality days have been in the "Unhealthy" range. Local air quality has continued to improve, and the number of days in the unhealthy ranges has been declining.
When air quality exceeds or is forecast to exceed the air quality standards, the elderly, the very young, or those with certain health problems should curtail their physical activity, especially during the afternoon hours.
"Smog" is measured as ground-level ozone concentration. To measure ozone concentrations in the air we breathe, outside air is sucked through long, candy-cane shaped glass tubes, where it moves to the ozone analyzer instrument inside each monitoring station. Inside the instrument, the air sample passes through a tube, where an ultraviolet (UV) light is shined on the air sample. The amount of UV light that passes through the air sample in the tube generates a voltage signal that is proportional to the ozone concentration in the specific air sample.
Carbon monoxide, sulfur dioxide, and oxides of nitrogen are also analyzed using complex methods and continuous analyzers.
Adverse health effects also occur due to microscopic-sized particles in the air we breathe. These are called "particulate matter" (PM). PM is monitored differently than the gaseous pollutants - it is collected on filters and weighed.
Air flows through the PM sampler like a vacuum. Very small particles pass through the intricate tubing and onto uncontaminated, pre-weighed filters. Afterwards, filters are weighed again in the District lab. The amount of PM pollution is determined by the weight of the PM collected on the filter and the volume of air that flowed through the sampler during PM collection.
The District monitors PM at regularly scheduled 24-hour periods. PM is sampled on separate instruments for 2.5 micron and 10 micron sizes. (Ten microns equals about one-seventh the diameter of a human hair).
Individual PM particles are too small to be seen, but collectively they are visible - sometimes in the "haze", in tailpipe smoke, or in windblown dust.
Because certain chemicals contained in PM samples can have health effects of their own, or can contribute to the formation of ozone through atmospheric interaction, some PM samples from certain District monitoring stations are also analyzed at outside laboratories for chemical content.
Just because you can't see air pollution doesn't mean it isn't there. That's why the District keeps a close watch on air quality levels day in and day out - to protect public health and welfare from the adverse effects of air pollution. Rain or shine, the District's Monitoring Division monitors the air we breathe throughout Ventura County's great outdoors.
For more information about monitoring the air or to
arrange a tour of the VCAPCD's lab or forecasting center,
call (805) 662-6959; or
write an e-mail to
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