MEXICO CITY (AP) — Mexico City officials issued their sixth pollution alert of the year Tuesday, but lifted it a few hours later after thunderstorms reduced pollution in the skies above the capital.

Such alerts automatically double from 20 percent to 40 percent the proportion of vehicles not allowed to circulate on a weekday. Normally one-fifth of the vehicles in the city and surrounding suburbs must stay at home each weekday, determined by license plate numbers.

The latest alert was declared Tuesday afternoon after ozone levels rose above 150 percent of acceptable limits. It also restricted activity at some gas stations and factories and banned the burning of solid or liquid materials.

Authorities suspended the alert around 9 p.m. following the rains.

Mexico City issued its first pollution alert in over a decade in March and continued high levels of contaminants have brought five more alerts. The pollution spike is due to seasonal weather patterns and the increasing number of cars in the city.