A new study has found that over two million deaths occur each year as a direct result of air pollution. Just last year, the Organization for Economic Cooperation and Development (OECD) issued a report that estimated the number of premature deaths from exposure to particulate matter (PM) is likely to more than double to 3.6 million in 2050, mostly in China and India. Premature deaths linked to ground-level ozone is also likely to be highest in China and India in 2050. The countries of North America, of Europe, Japan, Australia, and New Zealand though are not off the hook. According to the OECD report, they "are likely to have one of the highest ozone-related mortality rates in terms of number of deaths per million inhabitants --- second only after India --- due to the much greater aging of the population in these regions."

In any discussion of pollution, scientists most often point to airborne particulate matter and ozone. PM consists of a mixture of solid and liquid particles suspended in the air and continually varies over time and area in both size and chemical composition. "Bad" ozone, also known as ground level ozone, is not emitted directly into the air, but is created by chemical reactions between oxides of nitrogen and volatile organic compounds in the presence of sunlight. Motor vehicle exhaust, gasoline vapors, emissions from industrial facilities and electric utilities, and chemical solvents are among the sources of oxides of nitrogen and volatile organic compounds. These, then, are the essential components of pollution.

What Does Death By Air Pollution Look Like?

Unfortunately, many things.

As expected, studies have consistently shown an association between particulate matter air pollution and rising numbers of deaths from respiratory disease. The American Heart Association reports that "environmental air pollutants that include carbon monoxide, oxides of nitrogen, sulfur dioxide, ozone, lead, and particulate matter ... are associated with increased hospitalization and mortality due to cardiovascular disease, especially in persons with congestive heart failure, frequent arrhythmias, or both." And recent European studies have indicated that particulate matter contributes to lung cancer incidence.

Although air pollution is a major environmental health problem affecting everyone worldwide, the most vulnerable are the elderly, the poor, especially those in developing nations, and children. In particular, children experience the negative effects of air pollution most immediately as asthma.

Childhood Asthma

Asthma is a reversible obstructive lung disease that causes wheezing, breathlessness, chest tightness, and coughing. Asthma can be life-threatening when improperly managed. It is a chronic inflammatory condition and is caused by increased reaction of the airways to various stimuli. About one in 12 people (about 25 million) in the U.S. have asthma, and the numbers are increasing every year, according to the Centers for Disease Control and Prevention. The number of people diagnosed with asthma grew by 4.3 million from 2001 to 2009, and many of the faces behind these statistics are children.

Currently, 9.5 percent of all children have asthma. In particular, from 2001 through 2009, asthma rates rose the most among black children — almost a 50-percent increase. Many different factors have been associated with asthma, including genetic makeup, environmental tobacco smoke, dust mites, and cockroach allergens. Several studies have identified ozone and particulate air pollution as exacerbating elements among children afflicted with asthma. For years, researchers have linked air pollutants to increased acute respiratory illness, increased incidence of respiratory symptoms and infections, episodes of longer duration, and lowered lung function among children.

Not only is asthma on the rise in the U.S. but it is also becoming more widespread in other industrialized nations. During the 1980s, the prevalence of childhood asthma increased nearly 40 percent.

Rates and Reasons

Respiratory rates slow as we age; infants take anywhere from 30 to 60 breaths per minutes, toddlers 24 to 40, preschoolers 22 to 34, six to 12 year olds 18 to 30, adolescents 12 to 16 and adults eight to 20. Because of their faster rates, children breathe a proportionately greater volume of air than adults and so inhale more pollutants per pound of body weight. A child's physiological vulnerability is also increased by the fact that children are generally more vigorous than adults and often inhale more deeply. Their height and habits (playing on the ground, crawling, rolling) make them more likely to be exposed to pollutants or aerosols that are heavier than air; such pollutants tend to concentrate in a child's breathing zone nearer the ground. A final reason increasing children's vulnerability is the fact that they have narrower airways and their lungs are still developing.

Irritation caused by air pollutants, then, could significantly obstruct the airways of a young child while only producing a slight response in an adult.

Along with asthma, data gathered by a researcher suggest air pollutants may be associated with a variety of adverse health effects in children, including increased death rates in very severe pollution episodes and an increased risk of acute respiratory illness. Increased sickness rates, along with decreased lung function, as indicated by kindergarten and school absences, have also been observed among children subjected to air pollution.

While the effects on children can be studied, the vulnerability of another group has not yet been precisely quantified or understood.

Fetal Exposure

Findings reported by researchers from Columbia University indicate that carcinogens in ambient air can be transferred transplacentally from the mother to the fetus. The study conducted in Poland included 160 mothers and 160 newborns. The newborns who had been exposed to a variety of environmental toxicants showed decreased birthweight, length, and head circumference. "These results document ... that the fetus is more sensitive to genetic damage than the mother," stated the authors.

Finally, a study published last month finds perinatal exposure to air pollutants may increase the risk for autism spectrum disorder (ASD). Researchers from the Harvard School of Public Health estimated the link between levels of hazardous air pollutants at the time and place of birth and the number of cases of autism spectrum disorder in children who participated in the Nurses' Health Study II (325 cases of ASD out of a total population of 22,101). They found perinatal exposure to the highest quintile amounts of diesel, lead, manganese, mercury, methylene chloride, and overall measure of metals to be significantly associated with ASD when compared with the lowest quartile of perinatal exposure: the ratios ranged from 1.5 (the mothers in the highest level of exposure to overall metals had a one-and-a-half-times increased risk of giving birth to a child who developed ASD when compared to mothers in the lowest level of exposure) to 2.0 (the mothers in the highest level of exposure to diesels and mercury were two times as likely to give birth to a child who developed ASD when compared to the mothers in the lowest level of exposure).

For most pollutants, the researchers found the association to autism spectrum disorders were stronger among boys (279 cases) than girls (46 cases) and significantly different according to sex for each pollutant.

Sources: Roberts AL, Lyall K, Hart JE, et al. Perinatal Air Pollutant Exposures and Autism Spectrum Disorder in the Children of Nurses' Health Study II Participants. Environmental Health Perspectives. 2013.

Perera FP. Study of Effects of Environmental Pollution on Women and The Developing Fetus. Environmental Health Perspectives. 1994.

Raaschou-Nielsen O, Andersen ZA, Beelen R, et al. Air pollution and lung cancer incidence in 17 European cohorts: prospective analyses from the European Study of Cohorts for Air Pollution Effects (ESCAPE). The Lancet Oncology. 2013.