The state issued fewer ozone air pollution alerts in Maricopa County in 2009.
Since April, the Arizona Department of Environmental Quality issued 31 health watches and six high pollution advisories.
Last year, there were 44 health watches and 11 high pollution advisories for the Phoenix area.
State and county officials say fewer air pollution alerts may be attributed to people driving less, using light-rail and lower June temperatures that kept ozone levels in check.
Health officials say ozone pollution can cause or worsen health problems for people with asthma making it more difficult to breathe when ozone levels rise.
The 2009 ozone reporting period in Maricopa County ended Wednesday.