In May, the government said that air quality levels in Mexico City and its surrounding areas were the worst in 14 years.
Cap-and-trade systems put limits on companies' greenhouse gas emissions. Firms that produce emissions below their cap are able to sell their excess allowances to other businesses polluting above their limit.
A gasoline spill, caused by an illegal pipeline tap, polluted the creek and river of Paso Guayabo in the municipality of Matías Romero.
The Metropolitan district of Cuajimalpa presents 144 ozone points, well over the tolerable levels.
A new report will be issued Wednesday morning.
The traffic restriction will continue until 10:00 p.m.
The contingency is activated when the levels reach over 150 points.
Up to 145 IMECA points were measured in the municipality of Naucalpan.
Ozone, a key component of smog, reached almost 1.8 times acceptable limits.
The air quality exceeded the tolerable levels in six different locations.