The air around the Twin Cities and Rochester is pretty bad this week, thanks to a combination of heat, pollution, high barometric pressure and low winds.

And now, courtesy of the Minnesota Pollution Control Agency (MPCA), there is a website that can tell you just how bad.

The MPCA's new Air Quality Index website provides current air quality conditions for nearly the entire state, along with maps, graphs, and daily and monthly data summaries for 25 cities and five different air pollutants.

The information is especially important for people with health conditions that are made worse by smog and other types of air pollution.

The MPCA issued an alert Sunday because of high ozone levels, which in the Twin Cities topped out at 104 on the air quality index — a red alert.

By Monday, levels had dropped into a normal range, but ozone tends to peak between noon and 9 p.m. as temperatures rise, and state pollution officials said they expected the levels to creep back up later in the day.

The smog alert didn’t prevent paddlers and swimmers from enjoying Lake Calhoun on Monday.

Ozone can be of particular risk to people with respiratory or cardiovascular conditions, children, the elderly and people who spend long periods of time outside for work or exercise. High ozone levels can cause difficulty breathing, discomfort, coughing or sore throats. It can aggravate asthma and even cause heart attacks in susceptible people.

Ozone is produced on sunny days, when temperatures climb above 90 degrees, by a chemical reaction between small particulates from cars, engines, wood burning and small motors and other air pollutants. High air pressure and low winds allow pollutants to be trapped and build up over the course of the day. It can also be made worse by wildfire smoke carried into Minnesota from hundreds of miles away. This week, fires in Canada are contributing to the problem.

Cassie McMahon, air quality research analyst for the MPCA, said the website was created to help vulnerable people avoid problems and to encourage others to do what they can to reduce pollution. During alerts, vulnerable people should avoid exercising outdoors. Others should try to drive less, skip the back-yard fire and the use of gasoline-powered tools such as lawn mowers and leaf blowers.

McMahon said that in other metropolitan areas, making detailed information about air quality available to the public has been shown to make a difference, both among those who are vulnerable and among people's behavior in general.

Josephine Marcotty • 612-673-7394