Don't mention PM2.5 - ozone is a new threat

Shanghai Skyline in thick Fog
Official reports show that Beijing's fine particle pollutant (PM2.5) pollution index improved significantly in the first half of this year. I have just hoped for this, and I read a wave of media reports that followed the official so-called another major threat in the air, ground-level ozone (O3). Ozone pollution is mainly caused by the chemical reactions of oxides from automobile exhaust, factory exhaust gases, and smoke containing chemicals with sunlight. Recent media reports and the China National Environmental Monitoring Center have clearly pointed out that this summer, on some hot and sunny days, the highest index of pollutants is often ozone, rather than the usual PM2.5. However, is ozone really more harmful to human health than PM2.5, which has been well studied? If so, do we usually wear masks and indoor air purifiers for any protection?

Most of us have an understanding of ozone through discussions about global warming. It is because of the increasingly thin ozone layer in the upper atmosphere that we are protected from the sun's ultraviolet radiation. But near the ground, ozone is very destructive to our lungs, not only causing short-term and long-term harm but also increasing mortality. The concentration of ozone is always at its highest in the sunny afternoons of summer when the ultraviolet rays emitted by the sun react with the chemicals in the air, especially the toxic fumes from the infamous old diesel trucks. Most active. The World Health Organization's Air Quality Reference Index published in 2005 recommended a safe ozone concentration of fewer than 100 micrograms per cubic meter (8 hours of exposure to a polluted environment). If the ozone concentration is higher than 160 micrograms per cubic meter, it will have an unhealthy effect on children and lung patients who are relatively weak. If the ozone concentration is higher than 240 micrograms per cubic meter, it will be harmful to everyone. The China Environmental Protection Agency's reference index follows the World Health Organization's medium-term goal of 160 micrograms per cubic meter, while the US Environmental Protection Agency's Air Quality Index defines a safe "green area" below 120 micrograms per cubic meter.
In the heatwave in mid-July in Beijing, the ozone concentration in the afternoon often exceeds the three critical values ​​mentioned above—typically above 200 micrograms per cubic meter, up to 299 micrograms per cubic meter. In Los Angeles, the United States, which has long been the most polluted city in the United States, there are often days when the ozone concentration exceeds 200 micrograms per cubic meter, but it is already better than the ozone concentration of more than 400 micrograms per cubic meter decades ago. many. Therefore, although the ozone concentration in Beijing is not as dangerous as PM2.5 (the average PM2.5 concentration in Beijing in 2014 is 86 micrograms per cubic meter, which is much higher than 18 micrograms per cubic meter in Los Angeles), but often Unhealthy range.

Comparison of ozone and PM2.5

When it comes to symptoms, ozone seems to cause adverse reactions faster than PM2.5. When you go out on a hot summer day, you may notice that your eyes are stinging, your head is jumping, your throat is hot, coughing, and you feel a little out of breath. Personally, I am sometimes troubled by these symptoms while riding a bicycle to the clinic, especially during the evening peak hours, because ozone concentrations tend to be the highest at that time. Fortunately, I haven't had any more severe symptoms like asthma attacks, but I'm really worried about the effects of ozone on children, especially those who live on sunny, busy streets with asthma. Not only that, but healthy headaches are also risky. A 2002 survey was thought-provoking, investigating a group of healthy children living in southern California, hazy. Children exposed to outdoor sports are three times more likely to develop asthma than children who remain indoors most of the time due to exposure to ozone pollution.

But which kind of pollutant is more dangerous, is it PM2.5 or ozone? The US Air Pollution Action Plan for schools lists PM2.5 and ozone as pollutants that are equally dangerous for children. Regardless of PM2.5 or ozone, as long as the air quality index exceeds 200 (equivalent to an ozone concentration of 225 micrograms per cubic meter for an 8-hour exposure), the school needs to have all children indoors. For children with asthma, the action plan recommends a tighter critical range of air pollution indicators – 100 to 150.

But does this mean that we should really change some living habits in Beijing? Should we take different countermeasures against the current PM2.5 to deal with ozone?

To be honest, I don't think we need to make the corresponding changes to ozone. Although the World Health Organization's Air Quality Reference Index and a recent survey by the US Environmental Protection Agency show that ozone pollution is positively correlated with mortality and lung disease incidence, in my opinion, long-term data on ozone does not appear to be like PM2.5 is just as worrying. For example, PM2.5 is clearly carcinogenic and officially appears on the World Health Organization's list of carcinogens, but data on ozone does not show a strong correlation between ozone and cancer. In addition, the direct destruction of the heart by PM2.5 has been well documented, and the data on ozone has not established such a definitive correlation.

However, although ozone is not as dangerous as PM2.5 in the long run, short-term symptoms are more likely to plague each of us, especially now in the summer. People at high risk or commuting in environments with high ozone concentrations – including those on buses, taxis and subways – should consider wearing ozone-resistant masks. Even if you are young and healthy, you should consider wearing an ozone-resistant mask once you feel that the symptoms caused by ground-level ozone are serious.

The problem, however, is that most of the masks that deal with PM2.5's carbon-free filter materials have only a limited effect on the tinyer ozone molecules. One study has shown that this type of filter material can only remove one-third of the ozone. The most effective way to remove ozone with a mask is to add a layer of carbon to it. These special anti-Ozone masks were originally designed specifically for welders and are not intended for the average consumer. Welding is an especially dangerous occupation because the high temperatures during welding can produce very high concentrations of ozone, which is more than 12 times that of the US Occupational Safety and Health Administration. Therefore, the incidence of lung disease (including asthma) in welders is much higher than in the general population.

Several carbon masks have been used on the market to take advantage of this special technology. The above study and another updated study show that carbon-containing disposable masks, such as the 3M 9913, which is 90% effective for PM2.5, can remove 98% of ozone when properly used. I think this is still very remarkable. More importantly, studies have also shown that carbon-containing masks stabilize lung function, and carbon-free masks reduce lung function. In addition, the carbon layer of the carbon mask can still filter impurities very effectively after 40 hours of use. This means that office workers like me can bring these masks to and from work, and each mask can be used for at least two weeks. After it is dirty, or in most cases, the rubber band is broken first, you can throw it away.

Indoor air

Little girl with toys wearing a protective maskLittle girl with toys wearing a protective mask is generally only 40% to 50% of the outdoor pollution level, but because our indoor time is much longer than the outdoor time, a study estimate shows that we are exposed. 25% to 60% of the ozone comes from indoors.

Fortunately, the solution to this problem has been adopted by many of us - buy an air purifier. You may have found that a better quality air purifier already includes a layer of activated carbon filter and a layer of HEPA filter, both of which remove PM2.5. Indoor ozone is not as dangerous as PM2.5 and carcinogenic toluene and formaldehyde gases. In China's newly renovated houses, the concentration of similar volatile gases is often high due to the lower cost of furniture, walls and floors. The carbon filter of the air purifier is very effective in removing ozone and these volatile gases.

My bottom line

I have had several serious asthma attacks recently. Although I have recovered now, I am still worried about the recurrence of my condition. In light of a recent series of reports on ozone in the media, I have decided that the only change I need is to wear a carbon mask (also containing N95 material) to work on days with high ozone concentrations. Now whenever I use a mobile phone application that displays a pollution index, I will take a look at the concentration of ozone in addition to the concentration of PM2.5. I am very safe at home because my indoor air purifier contains activated carbon and HEPA filter.

During this summer, I also pay special attention to children and patients with asthma. I want to make sure that they know more about the specific hazards of people in the hot weather. As always, living in Beijing requires a combination of common sense and public health education. For ozone, taking a lot of the same protection strategies as dealing with PM2.5 should keep most people healthy.

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