Research Features

Fresh Air for the Future

Today it is a fact of life that the air we breathe can pose a threat to our health and well-being. Many of us who live in major cities check our local air quality index alongside the daily weather as we sip our morning coffee. Images of city skylines rising from a soup of yellow-brown are not an unfamiliar site in world news. For instance, pollution in Beijing was a major story during the 2008 Olympics, where millions of cars were removed from the roads as organizers implemented emergency measures to reduce airborne pollution before athletes and spectators arrived (ref. 1).

Photo on sunset Los Angeles smog

A familiar image of air pollution for Americans — sunset on a smoggy summer day in Los Angeles during the early 1990s. The tallest buldings of downtown and the Los Angeles river are a few landmarks barely visible through the haze. (Image credit: NASA/JPL/Barbara Gaitley)

Concerns over the quality of the air we breathe date back decades in the United States. The Federal Clean Air Act was introduced in 1963, and brought about a series of regulations (particularly with the amendments of 1970, 1977 and 1990) that were meant to control air pollution and protect citizens from airborne contaminants. The current policies that the United States Environmental Protection Agency has in place are expected to prevent 230,000 premature deaths by the year 2020 (ref. 2). But that's just in the United States. Air pollution is a global problem, and countries in every corner of the world are now implementing air quality indices and mitigation strategies to help tackle the issue.

Many strategies for reducing airborne contaminants have been proposed around the globe. Recently, a team of scientists, including members from the NASA Goddard Institute for Space Studies (GISS), examined fourteen specific emission control measures that target two major pollutants: ozone and black carbon (BC). The goal was to determine if, and to what extent, these control measures would affect global premature deaths linked to these two pollutants. The results of their study show that it might not be too late to ensure a breath of fresh air for the future of humankind.

Oh-No Zone

Ozone (O3) is a natural component of our planet's atmosphere. In the stratosphere (the second layer of our atmosphere, which lies just below the mesosphere), ozone makes up what we call the "ozone layer". This natural barrier helps protect the Earth from harmful solar radiation. Ozone is also present much closer to the surface of the planet in the troposphere, a region that includes the air we breathe. Down here in the troposphere, ozone can be a dangerous pollutant.

Diagram showing the layers of the atmosphere

The troposphere is the region of the atmosphere that is closest to the Earth's surface and includes the air we breathe. (Image credit: NASA ESPO/INTEX-NA Educational Outreach)

In the upper layers of the troposphere, ozone acts as a greenhouse gas. It absorbs some of the infrared energy that the Earth emits causing a warming effect that is contributing to the global climate change we're experiencing today. In the lower troposphere, ozone has direct effects on the health of our planet's biosphere. Many studies have shown that ozone can cause respiratory problems for people, linking the pollutant to conditions like asthma, bronchitis and premature death.

Human activities like fossil fuel consumption, rice production, landfills and livestock have caused a major increase in tropospheric ozone on our planet in the past centuries. These activities don't directly produce ozone, but they do produce ozone precursors — like nitrogen oxides, carbon monoxide and methane.

Black Skies

Like ozone, black carbon (BC) has been shown to cause numerous respiratory problems in humans. BC consists of airborne particles left over from the incomplete combustion of gas and biomass. Basically, it's tiny pieces of soot left behind after burning things, and it floats around in the air we breathe long after the fires have been put out and the engines have been turned off. There are natural sources of BC on Earth, but humans also dump a lot of the stuff into the air. It's created by everything we burn, from firewood and coal to forests and diesel fuel, and is produced in both our factories and our households.

Photo of field burning Satellite photo of smoke plumes from field burning

The use of biofuels in developing countries and biomass burning in the tropics have also contributed to increases in tropospheric ozone. In some areas, such as Zambia, the practice of field burning is visible to orbiting satellites. (Image credits: left, NASA; right, NASA/GSFC/MODIS)

With the introduction of various pollution controls in the United States and Europe, much of the BC produced in these regions has been decreasing since the 1950s. Today, most of the human-produced BC in the air comes from developing nations in Asia, Latin America and South America. Unfortunately, this trend of increasing BC production in the developing world shows no sign of slowing down.

Gasping for Breath

In their study, the team of researchers examined the effects that emission control measures could have on the future of Earth's air quality. Specifically, they focused on 14 measures that targeted methane (the ozone precursor) and BC. Using two composition-climate models (models that include trace species in the atmosphere, their chemical interactions with one and other, and the physical processes like winds, radiation and clouds that are important to climate), the researchers examined how decreasing methane and BC concentrations in the air would translate to reducing ozone- and BC-related deaths.

"The model takes as inputs emissions of various pollutants," explains Drew Shindell of the Goddard Institute for Space Science and contributing author on the study. "It then calculates the space and time varying influence of those emissions on the composition of the atmosphere as chemical reactions and various processes — such as rain — remove compounds. Finally, the impact of the composition changes due to the 14 measures on climate is calculated in the model. Health impacts are assessed based on the impact of the measures on surface level pollution."

Photo of diesel exhaust

Diesel exhaust is a prominent source of black carbon emissions. (Image credit: New York State Department of Environmental Conservation)

To decide on the 14 emission control measures that they would examine, the team first looked at emissions policies and recommendations that exist today. They used five emissions scenarios developed for the United Nations Environment Programme (UNEP) and the World Meteorological Organization (WMO). These scenarios included five cases. The first case was based on emissions data in the present day (2005) and the emissions policies that are now in effect (such as automobile emissions standard in the US and Europe). The second included emissions projected for 2030, and incorporated estimates of energy usage from the International Energy Agency and all the emissions policies that have been agreed on so far.

The third, fourth and fifth cases included varying degrees of additional emissions controls that have been suggested, but have not been agreed or implemented as of yet. This ranges from simply improving cooking stove technology to reduce the BC they produce (i.e. not a lot of new controls), to eliminating all high-emitting vehicles and agricultural waste-burning (i.e. very stringent emission controls). After sifting through all of this data, the team arrived at 14 measures ranging from relatively low emission control to very stringent policies affecting methane and BC production.

When the 14 measures were examined using the two climate models, the results were clear. Both models showed that BC and ozone concentrations would change dramatically, and would "substantially affect air pollution-related mortality around the world" (ref. 3).

A Cleaner Future

According to the study, regulations that are currently in place in North America will prevent 100,000 to 800,000 premature BC-related deaths per year by 2030. In East Asia, Southeast Asia and the Pacific, the number of lives saved could be as high as 1.1 million a year. However, the effects in Asia could be off-set (and possibly overtaken) by increasing BC and ozone concentrations in Southwest Asia and Central Asia, where emissions of these pollutants are expected to rapidly increase in the years to come.

When it comes to implementing new emissions measures, the results are brighter. The team estimates that if all the measures they examined were implemented, up to 4.4 million BC-related deaths and 520,000 ozone-related deaths could be avoided each year by 2030. Emissions measures would reduce mortality in all regions of the Earth, and could even reduce the current trend of increasing mortality due to air pollution in areas of Africa and Asia.

In all, up to 8% of all cardiopulmonary and lung cancer deaths among people 30 years or older could be prevented by the emissions controls. However, the researchers expect that these numbers actually underestimate the true benefits of reducing emissions.

"Indoor exposure would also be reduced, and as that currently kills even more people per year. Including indoor exposure would likely greatly increase the benefits of reducing emissions," says Drew Shindell. "There would also be benefits for children and young adults, who are not included in the study as epidemiological data is not available for those age groups."

Implementing emission controls would also have wider benefits beyond human health. When compared to greenhouse gases like carbon dioxide, methane and BC are relatively short-lived. This means that they don't hang around in the atmosphere quite as long. Reducing the concentration of methane and BC production would therefore have more immediate effects, and could lower climate change rates in the near term.

The results of the study are promising, and show that by controlling human-related sources of methane and BC, we still stand a chance at mitigating the harmful effects of these pollutants. Selecting and implementing the right measures today will help slow climate change, and will literally save millions of lives in the not-too-distant future.

Related Links

NASA Ozone Resource Page:


1 Watts, J, 2008: Beijing Olympics: Emergency anti-smog plan announced for 'Greyjing'. The Guardian. 28 Jul 2008. (Linklast verified May 3, 2019).

2 United States Environmental Protection Agency. The Clean Air Act (link last verified May 3, 2019).

3 Anenberg, S.C., J. Schwartz, D. Shindell, M. Amann, G. Faluvegi, Z. Klimont, G. Janssens-Maenhout, L. Pozzoli, R. Van Dingenen, E. Vignati, L. Emberson, N.Z. Muller, J.J. West, M. Williams, V. Demkine, W.K. Hicks, J. Kuylenstierna, F. Raes, and V. Ramanathan, 2012: Global air quality and health co-benefits of mitigating near-term climate change through methane and black carbon emission controls. Environ. Health Perspect., 120, 831-839, doi:10.1289/ehp.1104301.