Monday, May 6, 2013

Smog in Santiago

Santiago, Chile: April 30, 2013

Santiago has some of the worst air pollution of any city I've been to. Last week, I took a few pictures from my office that very vividly illustrate the problem here. The first is above, for the next few and some discussion, keep reading.

I work at Cerro Calan, in a small hill on the eastern part of town in the Las Condes sector. My office faces West, which allows me to see the greater part of Santiago on a clear day.
Some days are particular bad (like the photo above) and we can barely see the city or the distant mountains. When there's strong winds or rain, the weather clears out the smog and we get some beautiful views to the city.
A few days after I took the picture above, we got some long anticipated rain:
Santiago, Chile: May 3, 2013

In addition to snow capped mountains (the first of the season) we get to see much better air quality for a few days. Alas, a few hours after I took this picture, the smog started rolling back in.
The problem with Santiago is that it is in a valley between the Andes and the Chilean Coastal Range, has heavy vehicle traffic, and typically has dry weather. Hence, air is trapped within the valley and stays there until rainy or windy weather drive it away.

Air pollution can be measured in various ways, such as the amount of ozone or nitrogen oxides in the air. In Santiago, we get warnings based on the amount of breathable particulate matter. This is denoted as PM10 (MP10 in Spanish), where the 10 represents the maximum size of the particle considered (10 micrometers). There's also an PM2.5 index which consideres even smaller particles. These quantities are measured in micrograms per cubic meter.
The World Health Organization (WHO) recommends PM10 not exceed 50 micrograms per cubic meter in a 24-hour average. For a year, the average should be below 20. Unfortunately, Santiago exceeds these limits.

PM10 values for Las Condes in Santiago. Credit: SINCA

The plot above shows the daily PM10 measurements from 1997 to 2013 for the Las Condes region of Santiago. The blue are historical records, orange are last year's values, and the green are the current year's measurements. At the bottom, you can see the averages for all three color/times. PM10 is above 50 micrograms per cubic meters for Las Condes, on average.

However, my office is in Las Condes. When I look out my window I am facing the rest of Santiago, so how does that fare in comparison?
Unfortunately, it's worse:
PM10 values for Santiago Centro. Credit: SINCA

Above is the same plot, with the same scale, but for the central Santiago area as measured from Parque O'Higgins. On average, PM10 is more like 70 micrograms per cubic meter in the central parts of Santiago. Sure, some days are better, but this is not good for one's health.

You may notice the PM10 levels cycle between high and low regions. In the time axis of the plot, the first two digits represent the year, then the month, and finally the day. The peaks of the PM10 index happen around months 5-7 (May-July, austral Winter) whereas the lowest levels are 6 months later (Nov-Jan, austral Summer).
Smog is produced as sunlight drives chemicals reactions between nitrogen oxides to produce ozone and other compounds. In the Winter, there is a layer of cold air that traps the smoggy air close to the ground. This temperature inversion during Winter prevents the smog from dissipating, an effect further worsened by the topography of Santiago (ie, the surrounding mountains). Hence, while the conditions to produce smog are present year-round (lots of pollutants like cars, trucks, etc, and plenty of sunshine), during Winter the smog can get trapped for several days and grow very bad.

Want to know the current air quality in Santiago? Click here.

Finally, I'll leave you with a pair of pictures that show just how drastically the view from my office can change due to smog:
Santiago, Chile. Left: June 11, 2012, Right: May 18, 2012

1 comment:

  1. I currently live in Quito EC at elevation but with frequent rain and a much smaller population I do not see pollution.
    Still living in Santiago would be excellent.