Air Quality Monitoring

A clear view of a valley and mountains with bright blue skies A clear view of a valley and mountains with bright blue skies

Left image
Looking toward the Coachella Valley from Keys View on a day with good air quality.

Right image
The view on a day with poor air quality.

Why Monitor Air Quality?

Visitors to Joshua Tree National Park (JTNP) expect clean desert air and beautiful views. But though the park is protected in many ways, air pollution ignores boundaries. Haze often obscures mountain vistas, and in hot weather, ozone concentrations sometimes exceed levels safe for people to breathe. Polluted air also drops nitrogen compounds onto desert soil, where they act like fertilizer, helping invasive plants get a foothold.

The JTNP Air Quality (AQ) Monitoring Program aims to address these issues using monitoring and analysis methods put in place by the National Park Service’s Air Resources Division (ARD). The primary objectives of the JTNP program are to:
  • document current air quality conditions in the park;
  • identify the sources of pollution that affect park air quality;
  • track air quality trends using scientific data;
  • and understand how pollution affects park resources

With the information gained by long-term AQ monitoring, park managers can recommend actions to mitigate the impacts of air pollution.

Where Does the Air Pollution Come From?

Much of the air pollution that reaches JTNP starts as emissions from power plants, factories, and motor vehicles in the densely populated Los Angeles Basin and Coachella Valley. Westerly winds blow these pollutants into the park. Smoke from local and regional wildland fires, dust from construction projects near the park, and automobile exhaust from the growing number of park visitors also contribute to air quality problems at JTNP.

How Do You Monitor Air Quality?

AQ monitoring at JTNP focuses on measuring visibility, gaseous pollutants, and atmospheric deposition. Three automated monitoring stations collect most of the park’s air quality data. The primary station is located south of Black Rock Canyon Campground in the Mojave Desert region of the park, the area most impacted by air pollution.The station began reporting data in 1993. Two additional stations went online later at southern (Cottonwood Visitor Center, 2005) and eastern (Pinto Wells, 2007) sites in the park.

Instruments at the three stations measure ozone (O3), particulate matter (PM), and gaseous pollutants. Other instruments collect meteorological data such as air temperature, precipitation, relative humidity, and wind speed to help monitor climate change.

To maintain the accuracy of monitoring equipment, technicians make weekly site visits and conduct calibration checks. The California Air Resources Board also audits the stations annually.

Trends in Park Air Quality

In general, air quality at JTNP is holding steady or has improved slightly since monitoring began, but air quality remains a serious concern. Here are recent findings for some of the most worrisome pollutants.

Ozone. Ground level ozone, a respiratory irritant, has long been a problem in the northwestern part of the park. Ozone levels at the Black Rock site have improved since monitoring began, declining by 1.135 ppb, on average, each year between 1994 and 2019, possibly because of tighter controls on some industry emissions. Even so, ozone levels at Black Rock exceeded national health standards on 34 days in 2020, mostly during the months May–August. In fact, among the 38 national parks that monitor ozone, only Sequoia National Park routinely records more days exceeding ozone health standards. Exceedances are uncommon at the park's Cottonwood and Pinto Wells stations.

Visibility. The haze that interferes with long-distance views is quantified in units called deciviews. Between 2001 and 2019, visibility at JTNP improved slightly, declining on average 0.10 dv/year. But visibility is still impaired. In 2020 the measured visual range was between 48 and 153 miles; in clean air, park visitors should be able to see 119 to 206 miles.

Particulate Matter. Particulate matter includes solid particles and liquid droplets in the air: dust, smoke, soot, organic chemicals, and dirt in many shapes and sizes. These microscopic droplets and particles can enter the lungs and even the bloodstream. They are also the main cause of reduced visibility.

According to the ARD, particulate matter levels are "good" at JTNP, but with a deteriorating trend from 2011-2020. This change is likely due to development outside the park and wildland fires.

Nitrogen and Sulfur. Airborne nitrogen (N) and sulfur (S) compounds can harm ecosystems by increasing plant nutrients (N) and soil acidity (N & S). In recent years the deposition of nitrates and sulphates in precipitation has decreased, but ammonium (another N compound)and total nitrogen in precipitation are unchanged. Of concern is a likely increase in the dry deposition of nitrogen products; increased nitrogen in the soil may help invasive plant species outcompete native plants, which evolved to thrive in low-N soils. When non-native grasses dry out in late summer, they provide fuel for wildfires, which threaten plants like pinyon pines, juniper trees, and the park's flagship Joshua trees. Fires also further compromise air quality.

Bar chart tracking "number of exceedance days" by year, for the period, 2011-2020. The chart shows a general downward trend over time, with some noise, from 81 days in 2011 to 34 days in 2020.
Number of days each year that ozone levels have exceeded the EPA's National Ambient Air Quality Standards, 2011–2020.

NPS graphic

Management Applications

The JTNP air quality monitoring program shares its findings with park management and the NPS Air Resources Division. These findings steer management actions to mitigate air pollution impacts on biological and wilderness resources in the park.

The park notifies visitors and the general public about air quality through daily forecasts that are posted at visitor venters and entrance stations. Park staff also receive this information daily.

Joshua Tree National Park

Last updated: April 19, 2023