Why is this important?

Ozone in the upper atmosphere is necessary for our survival. Chemicals from car exhaust and some industries can react with sunlight to produce ground level ozone and smog, which are harmful to health. Severe smog can cause acute symptoms, such as shortness of breath and throat irritation. Even at lower levels, smog aggravates asthma and breathing problems, and slows plant growth.

What is the measure?

The charts summarize progress made toward meeting state ambient air quality standards.

How are we doing?

In May 2006, a new, more restrictive state 8-hour ozone standard was adopted. This standard, set at 0.07 ppm (parts per million), is intended to provide further protection for the public. Regulations require that all air districts attain these new standards at the earliest practical date.

However, the county is classified as "nonattainment" for this standard because we emit only a small percentage of the total emissions affecting our air quality. Pollutants generated and rising from the Central Valley are a critical factor in the county’s failure to meet the standards, and one over which we have no control. The state recognizes this by designating Tuolumne County as an Overwhelming Transport Area (see note at bottom of page), which does not require any regulatory action being implemented.

Another challenge is balancing air quality goals with the need to reduce wildfire risks through prescribed burning. Short-term exposure to smoke from prescribed burns is one of the trade-offs for reducing flammable forest fuels that could otherwise create extremely high levels of pollution from wildfires.

Note: Criteria For Assessing Whether an Ozone Nonattainment Area is Affected by Overwhelming Transport: Rural areas that demonstrate that transport of ozone and/or precursors into the area is so overwhelming that the contribution of local emissions to observed 8-hour ozone concentration above the level of the NAAQS is relatively minor and that emissions within the area do not significantly contribute to ozone concentrations measured in other areas (40 CFR 51.904). A rural area that is effected by ozone carried in from another area may be classified as an "Overwhelming Transport Area."

Days Tuolumne County Exceeded the
New California 8-hour Ozone Standard

Source(s): http://www.arb.ca.gov/adam/cgi-bin/db2www/adamtop4b.d2w/start http://www.arb.ca.gov/adam/php_files/aqdphp/sc8start.php
http://www.arb.ca.gov/adam/php_files/aqdphp/sc8display.php

Note: In 2006, the state standards changed from a 1 hour to an 8 hour measure, with the acceptable ozone concentration changing from .09 parts per million (ppm) to .07 ppm 2007 data is preliminary and subject to change