Tue, Mar 04, 2014 - Page 8 News List

Totting up every breath you take

By David Roberts and Nick Riesland

Fearsome stories about migrating Indonesian haze, post-Diwali smog in northern India and the return of the “airpocalypse” in China tell of Asia’s recent air-pollution woes. Not confined to Asia, outdoor particulate pollution claims over 3.1 million lives worldwide every year, five times the number of deaths from malaria and slightly less than double the current AIDS death rate.

Airborne pollutants, especially fine particles (smaller than 2.5 microns, or about the width of a strand of a spider’s web), enter deep into the lungs and from there enter the blood stream, causing cardiopulmonary disease, cancer and possibly premature births. Just how significant are these health risks?

Unfortunately, discussion of the subject is often opaque. Poor air quality is often described as reaching a certain air quality index (AQI) level, or as being a certain degree above a particular WHO standard. Yet the general public might better understand the situation if it were framed in terms that compare easily with more familiar hazards.

For instance, the immediate risks of breathing polluted air could be described in terms of the “micromort,” the unit representing a one-in-a-million chance of dying. An average person on an average day faces a risk of roughly one micromort from non-natural causes. This provides a useful starting point for comparison: The risk of scuba diving, for example, is around five micromorts per dive; sky diving is 10 micromorts per jump; and giving birth in the UK is about 120 micromorts. By comparison, breathing in Beijing on its most polluted days equals about 15 micromorts.

However, the more troubling risks from air pollution arise from chronic exposure. This can be expressed in terms of “microlives” — a unit developed by University of Cambridge statistician David Spiegelhalter to describe a person’s cumulative risks over a lifetime. One microlife represents 30 minutes of an average young adult’s expected lifespan. The average person uses up about 48 microlives per day, but lifestyle affects how fast one expends one’s microlives.

Settling in smoggy Beijing will use up an additional two to three microlives per day, implying a reduction in life expectancy of almost three years. Living in Hong Kong or Santiago, Chile, will cost one additional microlife per day, whereas daily life in New Delhi, one of the world’s most polluted cities, costs an estimated four to five microlives.

By comparison, smoking four cigarettes a day will cost the smoker around two microlives, about equivalent to living in Beijing. Yet the aging clock can also be slowed down — 20 minutes of daily exercise will extend life expectancy by two microlives per day (unless done in the smog), and drinking two or three cups of coffee daily saves an additional microlife per day. Furthermore, recent research suggests that some, if not all, of the microlives lost from living in Beijing could be recovered by moving to, say, Vancouver, with its pristine air.

Besides skipping town, one can mitigate at least some of the risks by limiting one’s exposure on particularly hazardous days. If citizens had access to current air-quality data, they could choose to take protective measures, such as minimizing physical exertion, staying indoors (ideally in filtered air), and wearing a mask (an N95-rated mask, at a minimum, not a surgical mask).

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