The vanishing ozone weekday/weekend effect.

Unlabelled: A national analysis of weekday/weekend ozone (O3) differences conducted using 1997-1999 data found that many urban areas experienced at least 5% higher 8-hr maximum O3 concentrations on weekends than on weekdays even though emissions of precursors were significantly lower on weekends. This phenomenon was observed mostly in urban areas in the Northeast, Midwest, and coastal California. A similar analysis using 2008-2010 O3 data shows that this phenomenon has mostly vanished.

Weekday/weekend ozone differences: what can we learn from them?

A national analysis of weekday/weekend ozone (O3) differences demonstrates significant variation across the country. Weekend 1-hr or 8-hr maximum O3 varies from 15% lower than weekday levels to 30% higher. The weekend O3 increases are primarily found in and around large coastal cities in California and large cities in the Midwest and Northeast Corridor.

Analysis of PM Trends in the United States from 1988 through 1995.

Because the U. S. Environmental Protection Agency (EPA) has changed the National Ambient Air Quality Standards (NAAQS) for ambient particulate matter (PM), there is a great deal of interest in determining recent PM trends.