In the early hours of Tuesday, thousands of residents in northern California, USA, received official warnings to stay indoors due to unhealthy levels of air pollution.
On that day, environmental authorities detected a critical increase in fine particles in areas such as Portola, Chester, and parts of Plumas National Forest.
The AirNow system reported unhealthy air quality at 4:00 a.m. ET in northern California, a pollution affecting health.
In particular, communities east of the Sierra and mountain valleys faced the most adverse conditions of air pollution.
The air quality index (AQI) recorded scores above 150 points, a threshold that triggered preventive measures for sensitive groups and the general public.
In California, air pollution exceeded normal limits
The PM2.5 particles reached concentrations exceeding 55 micrograms per cubic meter in the affected areas.
The Environmental Protection Agency (EPA) warned that these levels can affect even healthy people after several hours of exposure.
The interactive maps from AirNow showed red and purple colors dominating the region.
These shades represent unhealthy and “very unhealthy” air quality, respectively.
Therefore, the EPA recommended avoiding outdoor exercise, modifying physical routines, and rescheduling activities.
“When an unhealthy episode is detected, sensitive individuals should avoid any type of activity outside the home and stay in well-ventilated indoor environments,” the agency stated.
What happened in California and why air pollution levels spiked
The official records indicated that weather conditions kept cold air trapped near the ground.
This phenomenon favored the accumulation of PM2.5 particles from domestic burning, vehicles, and other minor sources.
Experts from the National Oceanic and Atmospheric Administration (NOAA) pointed out: “During thermal inversion events, polluted air does not circulate and pollutants remain concentrated in the lower layers of the atmosphere.”
Unlike previous episodes, this event was not related to large fires.
The main sources were activities associated with winter, agriculture, and weather phenomena that hindered natural ventilation.
Vulnerable groups and protection measures
The authorities identified the following groups as most vulnerable:
- Children and the elderly
- People with lung diseases
- Individuals with pre-existing heart conditions
- Population with chronic respiratory conditions
The NOAA advised checking hourly updates, as air quality can vary depending on air mass movement.
State authorities recommended not opening windows during pollution peaks to minimize the entry of particles.
The EPA manages the AirNow portal, where information is updated hourly.
The maps include reports for municipalities and rural areas, facilitating community and individual decision-making.
According to the latest EPA report, “the risks of PM2.5 are supported by a broad scientific literature on acute and chronic respiratory diseases, the main justification for the issued alert.”
Recent figures showed an increase in visits for mild respiratory conditions at local clinics during the days of higher pollution. However, no mass emergencies were reported.
Monitoring will continue in Portola, Chester, Plumas National Forest, and Sierra Valley until the air quality returns to safe categories according to federal parameters.
