As searing hot days continue this summer, heatstroke and heat exhaustion have sent record numbers of people to hospitals.

Drink lots of water, stay indoors and use air-conditioning, doctors say. But if you have irritated eyes or a sore throat, or feel dizzy or nauseated after being outside on a hot, windless day, you may be suffering from something totally different.

Chances are you have been exposed to photochemical smog, a form of air pollution that traces its history to the 1970s when Japan’s rapid industrial growth was not only driving an economic boom but also aggravating pollution.

Although the problem is long past its peak and it’s rarely life-threatening, its hazards remain very much real, as witnessed by municipal loud speakers set up in street corners that occasionally blare warnings as soon as dangerous levels of the pollutants are observed.

What is photochemical smog?

It’s a concentrated mass of an atmospheric pollutant called photochemical oxidants, appearing like a white fog shrouding the land when seen from a distance. These are secondary pollutants formed when primary pollutants — nitrogen oxides and volatile organic compounds in exhausts from factories and vehicles running on internal combustion engines — are exposed to strong ultraviolet rays from the sun.

The smog tends to occur on a hot summer day when the sky is clear and there is little wind, as photochemical oxidants need strong sunlight to develop and they are unlikely to concentrate into smog if there is a breeze to disperse them.

PM2.5 (particulate matter of 2.5 micrometers or less), which became a major concern in recent years as it drifted over Japan from China, is similar yet a different type of smog-forming pollutant created from nitrogen oxides and volatile organic compounds as well as sulfur dioxide.

Photochemical smog first became an issue in Japan in the 1970s when the nation’s industry was operating at high capacity and car ownership grew rapidly. While occurrences have decreased since then, they have never ceased and authorities still issue alerts for their potentially serious health effects.

In 2013, the combined number of days in which alerts were issued in prefectures nationwide reached 106, with most of them issued in July and August, according to Environment Ministry statistics. Tokyo topped the frequency ranking, followed by Kanagawa, Chiba and Saitama.

What are the symptoms and how can one avoid being affected?

Typical symptoms exhibited by people exposed to photochemical smog include irritation in the eyes, skin and throat, which can be accompanied by coughs, and reddened skin. In more serious cases, sufferers may feel like pins and needles in hands and feet, and have a headache, dizziness, fever, nausea and breathing difficulty.

Symptoms vary from person to person, but small children, elderly people and people with allergies are said to be more severely affected.

“The best way is to avoid going outside when an alert is on, but if you still become affected and feel irritation in the eye or throat, wash your eyes or gargle with water,” advises Hideka Kimura, director of the Air Quality Management Section at the Tokyo Metropolitan Government.

If symptoms persist or worsen, professional treatment is called for, which may include oxygen inhalation to alleviate breathing problems.

When seeing a doctor, Kimura says it helps to describe the circumstances under which the symptoms started.

An unfounded myth is that photochemical smog can be blocked by wearing an anti-pollen mask. Unlike hay fever, which is believed to be alleviated by wearing a mask to block cedar pollen and other substances that cause it, the smog’s molecules are too fine to be blocked by such masks. But some industrial-grade anti-dust masks are touted as being able to filter out the smog.

What alert system is in place to warn of photochemical smog?

Prefectural governments are responsible for monitoring concentrations of photochemical oxidants in their areas and issue alerts.

The Tokyo Metropolitan Government, for example, has set up instruments to measure the pollutants on the hour at 44 locations. The metropolis is divided into eight blocks, and separate alerts are issued for these blocks.

The metropolitan government issues four levels of alert, depending on the level of observed concentration between 0.1 and 0.4 parts per million.

“(The) graveness of symptoms can vary from person to person, and some people can be affected at the lowest level,” said Kimura of the metropolitan government.

The metro government has never issued the highest level warning.

It urges people to refrain from driving cars when alerts are on in order to limit the release of exhaust.

Are there information sources about photochemical smog alerts available in English?

Unfortunately, officials at the Meteorological Agency, the Environment Ministry and the metropolitan government contacted by The Japan Times said their alerts are only provided in Japanese.

That means non-Japanese-speaking people without immediate help from Japanese speakers are best advised to judge for themselves if conditions may be lining up for photochemical smog.

But as Tokyo gears up for the 2020 Olympics and expects a major increase in foreign visitors, Kimura said: “We’re feeling the need to provide information in not only English, but several other foreign languages.”

Some municipalities, however, do offer information in English, like Tokyo’s Minato Ward. The ward, which has a relatively large percentage of foreign residents, announces photochemical smog alerts in English through loud speakers set up on streets. The municipality also tweets and posts alerts on its website and Facebook page in English, Chinese and Korean.

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