California Counties Air Quality Ozone Levels & Grades

How is the air you are breathing in California? As a traveler, you may want to consider this question and evaluate the findings before you go. Why? If you have asthma or allergic reactions and are sensitive to fluctuations in air quality, you may need to take the appropriate medicines and treatments with you during your travels. In recent years, California consistently has had the most polluted cities in the U.S., coming in strong in the top 10 each year.

Ozone Concentration Air Quality in California Counties

Good 0.000 – 0.059 ppm

0.060 – 0.075 ppm Moderate (Yellow)
0.076 – 0.095 ppm Unhealthy for Sensitive Groups (Orange)
0.096 – 0.115 ppm Unhealthy (Red)
0.116 – 0.374 ppm Very Unhealthy (Purple)

County	Grade	Wgt. Avg.**	Orange Days	Red Days	Purple Days
Alameda	F	4.8	13	1	0
Alpine	A	0.0	0	0	0
Amador	F	12.0	27	6	0
Butte	F	14.5	39	3	0
Calaveras	F	10.8	28	3	0
Colusa	B	0.3	1	0	0
Contra Costa	F	4.3	13	0	0
Del Norte	A	0.0	0	0	0
El Dorado	F	35.0	82	14	1
Fresno	F	58.8	132	27	2
Glenn	B	0.7	2	0	0
Humboldt	A	0.0	0	0	0
Imperial	F	19.8	58	1	0
Inyo	F	8.3	25	0	0
Kern	F	102.8	228	51	2
Kings	F	36.8	95	9	1
Lake	A	0.0	0	0	0
Lassen	A	0.0	0	0	0
Los Angeles	F	91.5	182	51	8
Madera	F	14.5	39	3	0
Marin	A	0.0	0	0	0
Mariposa	F	24.7	66	4	1
Mendocino	A	0.0	0	0	0
Merced	F	23.8	56	9	1
Modoc	n/a
Mono	A	0.0	0	0	0
Monterey	B	0.3	1	0	0
Napa	C	1.0	3	0	0
Nevada	F	30.5	84	5	0
Orange	F	12.7	35	2	0
Placer	F	24.2	65	5	0
Plumas	n/a	n/a	n/a	n/a	n/a
Riverside	F	126.2	247	77	8
Sacramento	F	42.3	88	22	3
San Benito	F	5.0	15	0	0
San Bernardino	F	136.8	201	121	14
San Diego	F	29.5	81	5	0
San Francisco	A	0.0	0	0	0
San Joaquin	F	10.5	27	3	0
San Luis Obispo	F	23.3	67	2	0
San Mateo	A	0.0	0	0	0
Santa Barbara	F	6.3	19	0	0
Santa Clara	F	4.5	12	1	0
Santa Cruz	A	0.0	0	0	0
Shasta	F	7.5	21	1	0
Sierra	A	0.0	0	0	0
Siskiyou	A	0.0	0	0	0
Solano	F	3.3	10	0	0
Sonoma	A	0.0	0	0	0
Stanislaus	F	19.3	45	6	2
Sutter	F	8.3	22	2	0
Tehama	F	13.2	38	1	0
Trinity	A	0.0	0	0	0
Tulare	F	101.3	243	38	2
Tuolumne	F	16.5	42	5	0
Ventura	F	26.0	75	2	0
Yolo	F	4.5	12	1	0

The Environmental Protection Agency (EPA) has stations throughout the U.S. to measure a variety of chemicals, compounds and particulate matter in the air we breathe. Data from 3 recent years (2007-2009) shows that most California counties failed when it comes to acceptable ozone levels in the air. Unfortunately, counties are big places, and this data doesn't show targeted results for specific cities. It provide county overviews.

The data from the EPA was calculated over 3 years by the American Lung Association experts seeking to identify the number of days that 8-hour daily maximum concentrations occurred . At least 75% of the hourly concentrations (6-8 hours) had to be available for the 8-hour period. In addition, an 8-hour daily maximum average was identified if valid 8-hour averages were available for at least 75% of possible hours in the day.

Air Quality System (AQS) hourly ozone data collected by the EPA was used to calculate the daily 8-hour maximum concentration for each ozone-monitoring site. epa.gov & lungusa.org

**Weighted Average - The grades for ozone and short-term particle pollution are based on a weighted average for each county.

• Assign weighting factors to each category of the Air Quality Index.
• The number of orange days experienced by each county received a factor of 1; red days, a factor of 1.5; purple days, a factor of 2; and maroon days, a factor of 2.5.
• Multiply the total number of days within these categories by their assigned factor--1, 1.5, 2, 2.5 (maroon)
• Divide total by three (3 years measured)
• 1 entire day might get a B grade, and 3 days or more of higher concentrations of ozone in the air gets a an F grade.
  
  

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