Mexico City officials have issued a pollution alert for the capital and surrounding suburbs after ozone levels reached more than 150 percent of acceptable levels.

The alert triggers a reduction in the number of automobiles allowed to circulate in the city and the suburbs Friday as well as puts restrictions on some commercial and industrial activities.

The metropolis' Environmental Commission says a high-pressure system, weak surface winds and solar radiation have made it difficult for air contaminants to disperse.

It's the 10th such alert issued this year, and it's unusual coming during the summer rainy season when near-daily thunderstorms tend to flush out the smog. However, there was another alert July 8, also during the rainy season.