You Can Believe Your Eyes: Low Visibility Can Mean Higher Death Rates

  • Share
  • Read Later

Does it look like a bad day to go out for a run? Maybe a little too hazy out there? Here’s a tip: It is. Don’t do it.

A study released today by Hong Kong University and published in the journal Environmental Research has found that lower visibility due to pollution has a direct correlation with increased rates of mortality in Hong Kong. Researchers from the School of Public Health analyzed data on visibility and non-accidental mortality rates between 1996-2006, and found that for every four miles (6.5km) of loss in visibility, the increase in deaths by natural causes goes up 1.13%. Statistcally, that means that about 450 deaths can be associated with poor visibility each year. Between 2007 and 2010 alone, when the average visibility was about 7.8 miles (12.6km), 1200 deaths each year could be associated with poor visibility. (On a clear day, visibility is about 18.6 miles, or 30k. Last week, visibility in Hong Kong hit about 4.3 miles at one point.)

There goes the ‘it couldn’t be as bad as it looks’ mantra that we tell ourselves as we walk out the door every morning. It’s the first study correlating visibility and mortality to be conducted in Hong Kong, though similar studies have been done in other cities. (More on that in a moment.) That’s surprising because the worsening air quality is consistently a huge concern among residents of this otherwise fine city. According to two recent studies, 1 in 4 residents are considering leaving the city due to the bad air quality, and 91% of parents are worried how the it affects their kids’ health. In 1968, residents had to suffer about eight days of pollution-caused murk in a year. By last year, it was 46 days, or about one every week.

Most of the avoidable deaths in the study, according to Dr. Thach Thuan-quoc and one of study’s team members, were due to respiratory and cardiovascular disease. Though global studies have long linked those two diseases with air pollution, and specifically the high presence of particulates and nitrogen dioxide, using visibility as an indicator is a less examined approach. But this and other studies have found, as one would suspect, that visibility directly reflects the concentration of harmful pollutants in the air, and is therefore a useful tool to residents who are already at risk. “Looking out  the window can now function as a reliable way to gauge the danger to one’s health,” Joanne Ooi, CEO of Hong Kong’s Clean Air Network, said in a statement released today.

(See a list of the world’s most polluted places.)

The implications of the study are important, particularly in many parts of Asia. Being able to use visibility has a tool for measuring effects on health is particularly useful in the developing world where, despite the growing need for it, there still isn’t a lot of sophisticated equipment out there monitoring air quality. While residents in high-pollution areas can, as Ooi says, reliably use their own eyes to determine whether or not to overexpose themselves on a given day, scientists or health groups can use visibility data collected from airports and meteorological stations in most parts of the world to study pollutants’ health effects.

A 2009 study about the correlation between visibility and mortality over a year (2004-2005) in Shanghai – surprisingly, the first to be conducted in mainland China — found similar correlations between visibility and a rise in daily death rates in nine Shanghai neighborhoods. The study, authored by Haidong Kan of Fudan University in Shanghai, found that a decrease of 4.9 miles (8k) in visibility was associated with a 2.17% increase in total mortality, with a 3.36% increase in cardiovascular deaths and a 3.06% increase in respiratory related deaths. The group that was most affected was, not surprisingly, in the 65 and older age group. In a 2010 study published in the Indian Journal of Public Health, the association with mortality and  air quality, as measured by visibility, in the Punjab city of Ludhiana was even more significant: “For every 1 km (.6 mile) decrease in visibility at midday, mortality due to natural causes increased by 2.4%,” the study found.

It’s important to note, of course, that people live differently in different places. The level of exposure that somebody in the extremely densely populated spaces of Hong Kong or Shanghai might have every day to pollution might be greater than somebody might in a North American city.  (If you have ever spent a day walking around either, you’ll see what I mean. There is a reason you see people covering their mouths on every corner in Hong Kong as the buses go belching by.)

Both the study’s authors and environmental advocates take the government to task for their less-than-proactive approach to improving Hong Kong’s air quality. Professor Anthony Hedley, the principal researcher of the Hong Kong study, writes that the avoidable deaths uncovered in their data is just “the tip of a massive iceberg of harm to health that this ‘epidemic’ can extend more than 50 years. Air quality is unlikely to improve in the near future because the government refuses to adopt international guidelines for air quality management and health protection.” In a recent review of its Air Quality Objectives, the Environmental Protection Department identified that public health should be a cornerstone of the government’s impending new air quality plan. After the study was released today, the Clean Air Network immediately called for that long-promised plan to be adopted, and for the establishment of a special unit in the government to come up with a cohesive, health-based air quality policy.

Looking out the window of the Time office right now, I can’t say that sounds like a bad idea. I don’t have elderly relatives in this city who suffer from heart or lung disease, but millions do. And hopefully they’re inside.

If you live in Hong Kong and you want to sign up for an email alert to fill you in on the day’s pollution levels, you can do it here at the Clean Air Network.