OK, so when I flew into Mexico earlier this month I was astounded to see the brownish murk as my plane descended into the Valley of Mexico. The horizon disappeared, the mountains were invisible. After landing, the sky had a strange greyish tinge that persisted even when you looked straight up. My eyes watered. It was awful.
Back to the 1990s, I thought! The government declared a smog emergency, ultimately taking most cars off the road. By the time I flew out on the morning of Saturday, May 7th, the sky had gone back to a normal blue and you could see the mountains. Ozone levels had dropped from almost twice the safe limit (0.11 ppm) to “only” 2% above.
But it took heroic measures. The cutback on the number of cars in circulation was herculean.
Naturally, I wanted to see if things were really back to the 1990s. How bad was this smog emergency in historical perspective? Sadly, the data wasn’t easily available in one place. So I decided to get it. And after much looking, I managed to put together a complete series on the average maximum daily ozone reading for the Zona Metropolitana del Valle de México (ZMVM). That is to say, it takes the highest reading from all five metropolitan sectors for every day, then averages that across all the days of the month. The data from 1992 to 2010 (save 2003) are from INEGI, with the caveat that they changed the calculations in 2006 in a way that I do not fully understand. The data from all the other years are taken from hourly readings downloaded from the Atmospheric Monitoring Board of the D.F. government. I had to write some annoying Excel code to extract the data that I wanted, so I wouldn’t bet the bank on it having no errors.
Caveats aside, the numbers give a good idea of the trend:
Air quality has deteriorated markedly in the last three years, with spikes in May 2013, March 2014, April 2015 and ongoing for this year. But ... things are still better than they were when I left to work with Uncle Sam in 2002. And that despite an almost threefold increase in the number of motor vehicles in the metro area since then.
I was told several competing (but not necessarily exclusive) hypotheses. The obvious one is that the number of vehicles on the roads has finally outrun the decrease in smog per car. A complimentary one notes that congestion has markedly gotten worse with the increase in the number of vehicles ... and idling cars pump out more smog. Finally, the D.F. mayor decided to allow any car that could pass the smog check to get the coveted permission to hit the road every day of the week. It used to be that only newish cars could qualify; once the car got past a certain number of years, you could only drive it four weekdays out of five. That reform meant both that older cars could legally put out 25% more smog ... and, of course, some cars that should not have passed the smog check did with a little baksheesh.
And then there is the climate change hypothesis, but that is really a worry for the future.
But the future is coming fast. Even if things aren’t really back to the 1990s, it is clear that the government is going to have to do something fairly soon. The roads may be becoming saturated, but there is still lots of room for the number of vehicles on the road to increase. Traffic isn’t going to get better. And 2016 isn’t a fluke: as the data show, things have been getting worse for three years now.