The Mexican government is preparing to tighten vehicle emissions testing starting in July to tackle decreasing air quality.

Mexico City has seen its worst days of severe air pollution in years, and emissions testing is being seen as a solution to potential failures seen recently in restricted driving rules.

Critics assert that the government’s “day-without-a-car” program to keep a fifth of private vehicles off the roads six days a week has not been achieving its air quality goals and has been very unpopular with local residents.

Environment Minister Rafael Pacchiano said that the driving restrictions in place from April through June have helped to reduce emissions, even though two emergencies were declared. During these emergencies, the driving ban was extended to 40 percent of cars, including three days last week. The government had also lowered the pollution threshold for additional restrictions to be imposed.

Pacchiano said vehicles are the principal source of emissions that lead to a buildup of ozone, which can contribute to respiratory problems such as asthma. To enforce the rules that start on July 1, Mexican authorities will step up inspections at testing centers, including random retesting of vehicles.

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Critics of the “day-without-a-car” program say it encouraged people to purchase a second car with a different license plate number, as the ban is based on the last digit on license plates. This development has contributed to increasing traffic levels and higher pollution, they claim.

Pacchiano said the number of cars in the city has tripled to 5.4 million since the program was introduced last year. Newer cars had been exempted from the driving ban, but after the Mexico’s Supreme Court ruled that the exemptions should be based on emissions levels and not the age of the vehicles, many owners of older cars were able to secure the “zero” stickers. Between July and December of last year, 1.7 million vehicles switched to the “zero” sticker, which now account for 70% of the vehicles in the city.

Questions have come up from critics that program may have gone in the wrong direction, and the testing process has been called to question. A number of testing centers have been closed or fined for irregularities.

Critics also say that there are other likely causes of the air pollution problem, especially emissions from trucks and buses. There have also been persistent rumors that state oil company Petróleos Mexicanos, known as Pemex, was importing substandard gasoline from China. Pemex has denied receiving these imports from China.

Government officials are working together on longer-term solutions to the air pollution crisis. These possible measures include requiring all gasoline stations to have vapor recovery systems in place; reducing leakage of liquefied petroleum gas into the atmosphere; and a program to convert public transport vehicles to natural gas.

Wall Street Journal