Air Quality Monitoring

Continuous Countywide Outdoor Air Monitoring Smog Particles Learn more

Monitoring Stations

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Continuous Countywide Outdoor Air Monitoring

Ozone, carbon monoxide, nitrogen dioxide, particulate matter, sulfur dioxide and lead can be found in Ventura County’s air. These chemicals, called criteria pollutants, are harmful to our health, materials and agriculture.

That's why the district's Monitoring Division technicians, air quality specialists and meteorologists maintain and operate the sophisticated gaseous pollutant analyzers and particle monitors that determine the type and level of pollutants in the outside air at stations in El Rio (Oxnard), Ojai, Piru, Simi Valley and Thousand Oaks.

These monitoring stations also record near-surface atmospheric data because weather conditions are crucial to the formation and movement of air pollution. Sensors measure relative humidity, ultraviolet and solar radiation, barometric pressure, surface temperature, wind and precipitation. In addition, at the Simi Valley monitoring station, a remote-sensing instrument known as a ceilometer measures cloud height, vertical visibility and potential backscatter signals by aerosols thousands of feet above the surface.

For information about each station including real-time ozone and fine particulate levels, visit the Monitoring Stations page.

The district’s 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 are available on the Air Quality Data and Statistics page. Additional air quality data analysis is available from the district upon request. Air quality data for the entire state can be found on the California Air Resources Board Air Quality Data Statistics page.

Daily air quality, weather and agricultural burn statuses and forecasts for Ventura County are available on this district's forecast page. Local news media also report daily air quality using the Air Quality Index (AQI). Air quality conditions are identified as "Good," "Moderate," "Unhealthy for Sensitive Groups," "Unhealthy" (for all) or "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 falls in the unhealthy range, children, older adults and those with certain health problems should curtail their physical activity. For more AQI-related health guidance, visit the district’s Air Quality Index page.
 

Smog

Smog is measured as ground-level ozone concentration. To measure it, outside air is pulled into an ozone analyzer instrument inside each monitoring station. Inside the instrument, the air sample passes through a tube, where an ultraviolet (UV) light at a certain wavelength shines through it. 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 air sample.

Oxides of nitrogen are also analyzed using complex methods and continuous analyzers.
 

Particles

Microscopic-sized particles in the air we breathe called particulate matter (PM) also cause adverse health effects. The district’s monitors record ambient, or outdoor, particulate mass concentration levels using the principle of beta ray attenuation. Beta rays traverse a path through glass fiber filter tape before being detected. At the beginning of the measurement cycle, the beta ray count across clean filter tape is recorded. Then, an external pump pulls a known volume of PM-laden air through the filter tape, thereby trapping the PM on the filter tape. At the end of the measurement cycle, the beta ray count is re-measured across the PM-laden filter tape. The ratio of the hourly mass of collected PM on the filter tape to the volume of air is used to determine the amount of pollution.

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). The district monitors PM continuously at its five air monitoring stations.

Individual PM particles are too small to be seen, but collectively they are visible — sometimes in haze, smoke, exhaust or windblown dust.
 

Learn more

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 to protect public health and welfare from the adverse effects of pollution.

For more information about monitoring the air or to arrange a tour of the district's lab or forecasting center, call (805) 303-3890.
 

 

 

 

 

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