Warming world is expected to cause increasingly worse air quality for more than half the Earth's population

Monday, June 30, 2014, 11:18 AM - Earlier this year, the World Health Organization released a report stating that an estimated 3.7 million people around the world die prematurely every year due to smog and other outdoor air pollution. According to a new study out of Stanford University, climate change is only going to make those statistics worse, as regions of our atmosphere grow stagnant for longer periods of time, exposing more people to prolonged periods of poor air quality.

Let's face it. Our modern, industrial civilization pumps a lot of pollutants into Earth's atmosphere, even with the environmental regulations we have in place and the successes we've had in reducing or eliminating some of the worst of it (like sulphur dioxide and ozone-depleting CFCs). Most of the time, the weather patterns keep the air moving along at a fast enough pace that any pollutants emitted in a particular region are simply swept along and quickly mixed into the larger volume of the atmosphere. This usually prevents us from being too severely impacted by this pollution. However, once in awhile, weather conditions develop that slow everything down, trapping an area under the same air-mass for days at a time. This happens very easily in valleys, where the topography can prevent proper air flow, but you don't need mountains to get in the way for this to happen. Southern Ontario, southern Quebec and the Maritimes (along with all of the U.S. Northeast) can get socked in under a wide dome of high-pressure that gets trapped in place by the larger circulation patterns in the atmosphere. Southeastern China is prone to this as well. In this situation, the air pollution mixes into the same stagnant air, day after day, driving pollution concentrations up and the quality of the air we're breathing down. The longer the episode lasts, the worse the air quality gets.

This file photo shows the City of Toronto under a blanket of smog.

Air pollution inundates much of Eastern China, including the capital city of Beijing

Eventually, these stagnant weather patterns move on, bringing in some relief for those that suffered under them. However, new research by scientists with Stanford University's School of Earth Sciences and the Woods Institute for the Environment is telling us that we won't be able to count on these stagnant weather patterns moving on quite so often.

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"Since the 1960s, many nations have begun legislation-based initiatives to limit the amount of pollutants that can be emitted into the atmosphere. The U.S. policies have been effective at decreasing concentrations of the six most common pollutants by about 70 percent," Daniel Horton, a postdoc researcher at Stanford University who led the study, said in a press release. "Our new research suggests that global warming could impact some of that effectiveness by increasing the occurrence of stagnation. If so, the pollutants that do exist could accumulate more frequently, increasing the risk of poor air quality."

According to the press release, many studies have been performed that examine how the chemistry of air pollution will be affected by rising temperatures and the resulting increase in water vapour in the atmosphere. This new study, though, by Horton and his colleagues, is one of the few that sought to understand how the warming world will impact the three conditions that are required for stagnant weather conditions to develop:

1. lack of rainfall, which can imply sunny days that increase photo-chemical reactions or conditions where pollutants will not be 'washed' from the air by rain,
2. light or calm winds at the surface, which would keep air pollution very close to where it was emitted, and
3. light winds higher up in the atmosphere, which causes larger weather patterns to move along very slowly.

Using several different climate models together in an 'ensemble' model (which generally has more success in forecasting than each model does on their own), they watched for when all three showed up in an area at the same time.

"All three conditions have to occur simultaneously," Horton said in the press release. "If it doesn't rain on a particular day, but the winds are very strong, a stagnation event is not likely to occur."

Simulating how conditions will change in the case where emissions of carbon dioxide and other greenhouse gases continue unabated, resulting in a 4 degrees C rise in global temperatures by the end of this century, the models tracked along, recording how often the three conditions coincided and how long each stagnation event lasted. Their results showed that 55 per cent of the Earth's population will see increases in stagnation by the end of the century, and although some areas of the world saw less stagnation, 10 times as many people would see increases.

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Those regions expected to see the worst effects of this are in tropical or sub-tropical parts of the world - especially India, Mexico and the western United States - not only due to more stagnation and longer stagnation events, but also due to their large populations. China and nations along the Mediterranean Sea are also at high risk.

According to the report on this research in the journal Nature, there were two aspects that this study didn't include: increasing population and increases in the amount of air pollutants (particulate matter and ozone precursors) being released into the atmosphere. So, as the world population will definitely be increasing by the end of this century - to over 11 billion people - and if greenhouse gas emissions increase these pollutants will also definitely be increasing - as they are also byproducts of burning fossil fuels - these projections are conservative, to say the least.

The overall message from this study is that, although countries have pollution control measures in place, which are effective in the here and now, in the future they will not be enough to protect people. Only by reducing the amount of greenhouse gases emitted, along with reductions and controls on these other air pollutants, can the worst impacts be avoided.

For Canada's part, the federal government and its partners have developed the Air Quality Health Index (AQHI). This tool, which is a measure of local ambient air quality, rates short-term (acute) air pollution exposure levels, and provides health advice on the best times to be active outdoors. Your local air quality conditions and forecast are available here on The Weather Network (tune in at 16 minutes past the hour or click here), and you can learn more about the AQHI from Environment Canada website (click here).

Furthermore, the government has recently introduced new Canadian Ambient Air Quality Standards (CAAQS). Under the Air Quality Management System, Environment Canada and Health Canada have established these air quality standards for fine particulate matter (PM_2.5) and ground-level ozone (O₃) - two pollutants of concern to human health and the major components of smog - to reduce the risk of long-term (chronic) exposure. These new standards, which will come into effect in 2015, are more stringent and more comprehensive than the previous Canada-wide Standards for these pollutants.