The air in Humboldt, Del Norte and Trinity County is considered to be in "in attainment" of state and federal ambient air quality standards except for the State's 24-hour PM₁₀ standard for Humboldt County only. The two pollutants of greatest concern in the region are ozone and particulate matter.

Ozone is an invisible pollutant formed by chemical reactions involving nitrogen oxides, reactive hydrocarbons and sunlight. It is a powerful respiratory irritant that can cause coughing, shortness of breath, headaches, fatigue and lung damage, especially among children, the elderly, the ill and people who exercise outdoors.

Particulate Matter is fine mineral, metal, soot, smoke and dust particles suspended in the air. Primary sources of particulate matter in the Eureka area are on-road and off-road vehicles (engine exhaust and dust from paved and unpaved roads), open burning of vegetation (both residential and commercial), residential wood stoves, and stationary industrial sources (factories). For health reasons, we are most concerned with particulate matter less than 2.5 microns in diameter (PM_2.5). Particles of this size and smaller can permanently lodge in the deepest, most sensitive areas of the lungs, and cause respiratory and other health problems. The California Air Resources Board recently concluded that PM_2.5 is far more hazardous than previously estimated.

The District operates four air monitoring stations within its tri-county jurisdiction, and maintains a current Annual Network Plan for Ambient Air Monitoring which explains how air pollutants are monitored within the District.

The North Coast Air Basin is comprised of three air districts, the North Coast Unified AQMD, the Mendocino County AQMD, and the Northern Sonoma County APCD. The North Coast AQMD included Del Norte, Humboldt, and Trinity Counties; the Mendocino County AQMD consists of Mendocino County; and the Northern Sonoma County APCD comprises the northern portion of Sonoma County.

To view Area Designations for the rest of the North Coast Air Basin, and all other Basins in the state, please click here. You will be redirected to the California Air Resources Board Area Designation Maps.