路透社纽约健康消息 最新研究发现，空气中的臭氧水平只要轻微增长都会对儿童的健康产生不良影响，以致耽误他们的正常学习。空气污染已经成为学生因呼吸系统疾病而缺课的最重要原因。
位于地球大气层上空的天然臭氧可以阻挡太阳紫外线的辐射，对人体有保护作用。然而，逗留在地球表面的“人工臭氧”则是一种伤害性的污染物。这种“人工臭氧”由汽车排放出来的废气在光照作用下发生化学反应生成，被吸入人体后会引起咳嗽、呼吸急促、恶心呕吐等反应，并可造成永久性的肺损害，儿童和老人更容易受到损害。
美国的研究人员对空气中3种最常见的污染物：臭氧、二氧化氮和微尘进行了分析，并将分析结果同1996年上半年中2,081名4年级学生里每天的缺课率进行比较。这些孩子全都居住在洛杉矶附近方圆200英里范围以内。在电话采访中，研究人员针对学生的疾病原因，对所有的医生认为可能导致这种疾病的因素进行了一一记录，最终确定了学生们缺课的确切原因。
结果可以看到，在低于目前允许的空气臭氧水平标准以下的环境中生活的学生的健康正在受到损害。空气中臭氧水平仅仅增加十亿分之二十，因呼吸系统疾病而导致的缺课率就相应地增长83%，伴有咳嗽咯痰的下呼吸道疾病也相应地增长了173%。对另外两种污染物，微尘和二氧化氮的观察中，则没有类似的发现。
美国过敏·哮喘·免疫协会认为，臭氧可以对任何人造成损害，患有哮喘或支气管炎、肺气肿等慢性肺病的人更容易受到侵害。目前臭氧水平最高的几个美国城市包括洛杉矶、亚特兰大、菲尼克斯和休斯顿。美国环境保护局建议通过几人共用一辆汽车、公共交通、鼓励步行或骑自行车的方法来减少臭氧产生。
Air Pollution Linked to School Absenteeism
NEW YORK (Reuters Health) - Even small increases in the levels of the air pollutant ozone may adversely impact the health of children causing them to miss school, a new report suggests.
``We are seeing ill health effects in school children at levels well below the current air quality standard for allowable levels of ozone,‘‘ Dr. Frank Gilliland of the University of Southern California in Los Angeles, told Reuters Health in an interview.
Ozone is produced by a chemical reaction that occurs when sunlight hits air pollutants emitted in automobile exhaust. Breathing air with ozone can cause coughing, respiratory irritation, nausea and permanent damage to the lungs in people of all ages, but children and the elderly are especially vulnerable.
The investigators analyzed daily levels of three common air pollutants--ozone, nitrogen dioxide and fine particles--and compared them with daily absenteeism rates of 2,081 fourth graders during the first 6 months of 1996.
Gilliland‘s team also telephoned the parents‘ homes every time a child was absent from school.
During the telephone interview, the researchers determined the exact reason for the absence. If the reason was due to illness, they recorded all the information pertaining to the sickness, symptoms and outcomes from doctor or hospital visits. All of the children in the study lived within a 200-mile radius of Los Angeles.
As the levels of ozone increased in the air by as little as 20 parts per billion, the researchers saw a corresponding rise in absenteeism due to respiratory illness increase by 83%, explained Gilliland. In addition, the authors documented a corresponding increase of 173% in lower respiratory illness with wet cough.
``This indicates a potentially more serious type of illness involving the lungs, rather than just the nose or the throat,‘‘ Gilliland told Reuters Health.
``Air pollution has turned out to be surprisingly important factor contributing to absenteeism due to respiratory illness,‘‘ he added.
Similar findings for the other two pollutants--fine particles and nitrogen dioxide--were not observed, Gilliland and colleagues note in the January issue of the journal Epidemiology.
While ozone can affect anyone, people with asthma or chronic lung diseases such as bronchitis and emphysema are particularly vulnerable, according to the American Academy of Allergy, Asthma and Immunology.
When produced naturally in the upper atmosphere, ozone acts as protection from the sun‘s ultraviolet rays. But when man-made ozone lingers closer to earth, it is a pollutant that becomes harmful.
The US Environmental Protection Agency recommends car pooling, using mass transit, walking or biking to avoid contributing to ozone levels.
US cities where ozone levels are highest include Los Angeles, Atlanta, Phoenix and Houston.
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