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Air Pollution Is a Killer

Air pollution is a killer. It is responsible for more deaths than better known risk factors, such as alcohol use, physical inactivity, or unsafe sex.

Risk factors don’t usually kill you directly. Almost nobody steps off an airplane in Delhi or Beijing and dies from inhaling a breath of polluted air. Instead, risk factors make it more likely that you will get a disease, and that disease will either kill you or disable you. Using this logic, it is possible to say that all deaths are “caused” by some combination of risk factors, which lead to the specific diseases or events that kill the individual.

Figure 1. Number of deaths worldwide attributable to 17 risk factors. Source: Institute for Health Metrics and Evaluation, 2018.

Public health officials estimate the number of deaths that result from (are caused by) the various risk factors. For instance, if a person has high blood pressure and high blood glucose, and that person dies at age 68 instead of age 78, which was the person’s life expectancy, then that person lost 10 years of expected life. Public health officials try to figure out how many of those 10 lost years were attributable to the high blood pressure, and how many to the high blood glucose. They then assemble that data into a statistic that represents how many deaths per year were caused by each.

Figure 1 shows the number of global deaths per 100,000 in population that are attributable to the most important risk factors. Air pollution is 4th, behind high blood pressure, dietary risk (unhealthy food), and tobacco use. The total number of deaths attributed to air pollution in 2016 was 6.1 million, or 9.6% of all deaths from all risk factors.

The primary diseases to which air pollution contributed were heart disease, stroke, chronic lung disease (including asthma), and respiratory infections. Air pollution was responsible for more deaths than many better known risk factors such as high blood glucose, high cholesterol, alcohol and drug use, malnutrition, and unsafe sex (HIV/AIDS, etc.) In fact, despite all the publicity that unsafe sex gets, only 1.2 million deaths were attributed to it worldwide in 2016. Don’t get me wrong, 1.2 million deaths are a terrible thing, but air pollution kills more than 5 times as many.

Figure 2. Disability-adjusted life years (DALYs) attributable worldwide to 17 risk factors, 2016. Source: Institute for Health Metrics and Evaluation.

Risk factors don’t have to kill you, they can also cause disability. A person with a disability may live for many years before dying, trying to cope with that disability every day of every year. Thus, in public health terms, a disability incurred early in life has somewhat different implications than a disability incurred late in life. The Global Burden of Disease estimates not only the number of people with a disability, but multiplies it by the length of time they will have to live with it. This estimate is called the disability-adjusted life years (DALY). Air pollution is the 5th most important risk factor for DALYs, with malnutrition having vaulted into the lead position. (Figure 2)





Figure 3. Deaths per 100,000 attributable to air pollution, by country, 2016. Source: Institute for Health Metrics and Evaluation.

Figure 3 shows a map of the world onto which the number of deaths per 100,000 from air pollution has been charted. North Korea loses more of its population to air pollution than any other nation, followed by the Central African Republic, Georgia (the country, not the state), and Afghanistan. This may surprise many readers, as we often think of air pollution being a function of industrial emissions in large cities, but in many developing nations, this is not the case. Readers of this blog know that particulate matter is the most dangerous of the 6 criterion pollutants. In developing countries, the people often use fires inside the home for cooking and warmth. The fires are smokey, and the homes are poorly ventilated, resulting in high levels of particulate air pollution. In addition, blowing fine mineral particles play an important role in some desert countries.

The United States has a death burden from air pollution of 32.6 per 100,000: low, but not one of the lowest in the world.

The above data looks at number of premature deaths caused by air pollution. Another way to look at the data is by asking how much air pollution shortens an average person’s life. Just such a study recently appeared (Apte, et al., 2018). Supplementary data associated with that article estimated the average life span in the United States to be 78.8 years, and PM2.5 will take about 4-1/2 months off of the average life expectancy. That was 22nd best in the world. Sweden had the lowest loss of life expectancy from PM2.5, about 1/3 that of the USA, while Bangladesh had the highest, almost 5 times that of the USA.

So, what diseases has air pollution been implicated in? We know from the above that it is known to cause disability and contribute to early death. We know that it contributes to the development of heart attack, stroke, chronic lung disease (including asthma), and respiratory infection. These relationships have been well documented, and are strong. But air pollution has also been implicated in diseases you wouldn’t expect. It has been implicated in a host of neuropsychological conditions, from increased signs of inflammation in the brain, to increased rates of Parkinson’s disease, to reduced IQ, to increased risk of ADHD, to increased rates of autism spectrum disorders, to reduced motor functioning. It has been implicated in hastening cognitive decline late in life. It has been implicated in the development of obesity and type 2 diabetes.

My impression from the studies of air pollution’s relationship to mental functioning, obesity, and diabetes is that their conclusions should not be heavily relied upon, as confounding variables undercut the comparisons the authors try to make. Even when their findings hold up, air pollution seems to play only a small role in most of these diseases. Many of the studies enrolled large numbers of subjects, making it possible to find statistically significant results with small differences of questionable importance. This is sometimes hidden from view by reliance on the relative risk statistic. Relative risk compares the risk in one condition with the risk in another. For instance, suppose 2 people out a million of develop a disease. If people are exposed to air pollution, however, then 3 people out of a million develop the disease. The relative risk is 3/2 = 1.5, or 50% higher. That sounds really significant. But you have added only one case per million people, and in total only 3 people out of a million will get the disease. If you look at it that way, then it doesn’t seem so important. Investigators can make some pretty insignificant results sound mighty important by reporting relative risk and not reporting other statistics. Thus, air pollution may play a role in these conditions, but I think the jury is still out, and we will have to await further study to be sure of how important a role.

Don’t let the fact that air pollution may play rather minor roles in causing diseases such as Parkinson’s, Alzheimers, autism, or diabetes confuse you. It is strongly linked to heart attack, stroke, chronic lung disease, and asthma, and is a significant risk factor worldwide.

This brings me to the end of this update on the Air Quality Index data for 2017. Missouri has made large strides in improving air quality. It is one of the few good news stories I get to report on. It is important that we continue to make progress, however, as air pollution is an important risk factor that causes or contributes to a great deal of death and disability around the planet.


Alderete, Tanya L., Rima Habre, Claudia M. Toledo-Corral, Kiros Berhane, Zhanghua Chen, Frederick W. Lurmann, Marc J. Weigensberg, Michael I Goran, and Frank D. Gilliland. “Longitudinal Associations Between Ambient Air Pollution With Insulin Sensitivity, ß-Cell Function, and Adiposity in Los Angeles Latino Children.” Diabetes, 66, (7), pp. 1789-1796.

Apte, Joshua S., Michael Brauer, Aaron J. Cohen, Majid Ezzati, and C. Arden Pope, III. 2018. “Ambient PM2.5 Reduces Global and Regional Life Expectancy. Environmental Science & Technology Letters. Article ASAP. DOI:10.1021/acs.estlett.8b00360. Data downloaded 8/27/2018 from https://pubs.acs.org/doi/10.1021/acs.estlett.8b00360.

Berhane, Kiros, Chih-Chieh Chang, Rob McConnell, James Gauderman, Edward Avol, Ed Rapapport, Robert Urman, Fred Lurman, and Frank Gilliland. “Association of Changes in Air Quality With Bronchitic Symptoms in Children in California, 1993-2012.” Journal of the American Medical Association. 315. (14), pp. 1491-1501.

Caiazzo, Fabio, Aksay Ashok, Ian A. Waitz, Steve H.L. Yim, Steven R.H. Barrett. 2013. “Air Pollution and Early Deaths in the United States. Part 1: Quantifying the Impact of Major Sectors in 2005.” Atmospheric Environment. 79 pp. 198-208.

Costa, Lucio G., Toby B. Cole, Jacki Coburn, Yu-Chi Chang, Khoi Dao, and Pamela J. Roque. “Neurotoxicity of Traffic-Related Air Pollution.” Neurotoxicology, 59, pp. 133-139.

Dendup, Tashi, Xiaoqi Feng, Stephanie Clingan, and Thomas Astell-Burt. 2018. “Environmental Risk Factors for Developing Type 2 Diabetes Mellitus: A Systematic Review.” International Journal of Environmental Research and Public Health. 15 (78); doi:10.3390/ijerph15010078.

Di, Qian, Lingzhen Dai, Yun Wang, Antonella Zanobetti, Christine Choirat, Joel D. Schwarts, and Francesca Dominici. 2017. “Association of Short-Term Exposure to Air Pollution With Mortality in Older Adults. Journal of the American Medical Association. 318, (24), pp. 2446-2456.
Dockery, Douglas W., Arden Pope III, Xiping Xu, John D. Spengler, James H. Ware, Martha E. Fay, Benjamin G. Ferris, and Frank E. Speizer. 1993. “An Association Between Air Pollution and Mortality in Six U.S. Cities.” New England Journal of Medicine, 329 (24), pp. 1753-1759.

Guxens, Monica, and Jordi Sunyer. 2012. “A Review of Epidemiological Studies on Neuropsychological Effects of Air Pollution.” Swiss Medical Weekly. 141: w13322.

Health Effects Institute. 2018. State of Global Air 2018. Special Report. Boston, MA: Health Effects Institute.

Institute for Health Measurement and Evaluation. GBD Compare/Vix Hub. https://vizhub.healthdata.org/gbd-compare.

Jerrett, Michael, Rob McConnell, C.C. Roger Chang, Jennifer Wolch, Kim Reynolds, Frederick Lurmann, Frank Gilliland, and Kiros Berhane. 2010. “Automobile Traffic Around the Home and Attained Body Mass Index: A Longitudinal Cohort Study of Children Aged 10-18 Years.” Preventive Medicine. 50 (0 1), pp. S50-S58.

Jerret, Michael, Rob McConnell, Jennifer Wolch, Roger Chang, Claudia Lam, Genevieve Dunton, Frank Gilliland, Fred Lurmann, Talat Islam, and Kiros Berhane. 2014. “Traffic-Related Air Pollution and Obesity Formation in Children: A Longitudinal, Multilevel Analysis.” Environmental Health. 13, 49. http://www.ehjournal.net/content/13/1/49.

Miller, Kristin A., David S. Siscovick, Lianne Sheppard, Kristen Shepherd, Jeffrey H. Sullivan, Garnet L. Anderson, and Joel D. Kaufman. 2007. “Long-Term Exposure to Air Pollution and Incidence of Cardiovascular Events in Women.” New England Journal of Medicine. 356 (5), pp. 447-458.

Oudin A, Forsberg B, Nordin Adolfsson A, Lind N, Modig L, Nordin M, Nordin S, Adolfsson R, Nilsson LG. 2016. “Traffic-related air pollution and dementia incidence in northern Sweden: a longitudinal study.” Environ Health Perspectives. 124:306–312; http://dx.doi. org/10.1289/ehp.1408322.

Power, Melinda C., Sara D. Adar, Jeff D. Yanosky, and Jennifer Weuve. 2016. “Exposure to Air Pollution as a Potential Contributer to Cognitive Function, Cognitive Decline, Brain Imaging, and Dementia: A Systematic Review of Epidemiologic Research. Neurotoxicology. 56, pp. 235-253.
Ritz, beate, Pei-Chen Lee, Johnni Hansen, Christina Funch Lassen, Mattias Ketzel, Mette Sorensen, and Ole Raaschou-Nielsen. “Traffic-Related Air Pollution and Parkinson’s Disease in Denmark: A Case-Control Study.” Environmental Health Perspectives. 124 (3), pp. 351-356.

Samet, Jonathan M., Francesca Dominici, Frank C. Curriero, Ivan Coursac, and Scott L Zeger. 2000. “Fine Particulate Air Pollution and Mortality in 20 U.S. Cities, 1987-1994.” New England Journal of Medicine. 343, (23), pp. 1742-1749.
Schwartz, Joel, Marie-Abele Bind, and Petros Koutrakis. 2016. “Estimating Causal Effects of Local Air Pollution on Daily Deaths: Effect of Low Levels.” Environmental Health Perspectives. DOI:A10:1289/EHP232. http://dx.doi.org/10.1289/EHP232.
Wellenius, Gregory A., Mary R. Burger, Brent A. Coull, Joel Schwartz, Helen H. Suh, Petros Koutrakis, Gottfried Schlaug, Diane R. Gold, Murray A. Mittleman. 2012. “Ambient Air Pollution and the Risk of Acute Ischemic Stroke. Archives of Internal Medicine. 172, (3), pp. 229-234.
Weuve, Jennifer, Robin C. Puett, Joel Schwartz, Jeff D. Yanosky, Francine Laden, and Francine Grodstein. 2012. “Exposure to Particulate Air Pollution and Cognitive Decline in Older Women.” Archives of Internal Medicine. 172, (3), pp. 2190227.
White, Laura F., Michael Jerrett, Jeffrey Yu, Julian D. Marshall, Lynn Rosenberg, and Patricia F. Coogan. 2016. “Ambient Air Pollution and 16-Year Weight Change in African-American Women.” American Journal of Preventive Medicine. 51, (4), e99-e105.

Ozone Was the Most Important Air Pollutant in Missouri in 2017

The Air Quality Index is a measure that combines the level of pollution from six criterion pollutants: ozone (O3), sulphur dioxide (SO2), nitrous oxide (NO2), carbon monoxide (CO), particulate matter smaller than 2.5 micrometers (PM2.5), and particulate matter between 2.5 and 10 micrometers (PM10). For a brief discussion of these pollutants, see Air Quality Update 2017.

Figure 1. Data source: Environmental Protection Agency.

Figure 1 shows the percentage of days for which each of the criterion pollutants was the most important one. The chart combines all 24 counties together. Since 2009 ozone has been the most important pollutant on more days than any of the other pollutants, and it extended its “lead” in 2017. PM2.5 was the most important pollutant on the second highest number of days. Since 2007, however, the percentage of days on which it was the most important pollutant has been trending lower. One or the other of these two pollutants was the most important on 77% of all days statewide.

(Click on figure for larger view.)

Thirty years ago, ozone was a much less important pollutant than it is now. In 1983, it was the most important pollutant on fewer than 30% of the days statewide, but in 2017 it was the most important pollutant on 54% of the days. While we need ozone in the upper atmosphere to shield us from ultraviolet radiation, at ground level it is a strongly corrosive gas that is harmful to plants and animals (including us humans). We don’t emit it directly into the air. Rather, it is created when nitrogen oxides and volatile organic compounds (vapor from gasoline and other similar liquids) react in the presence of sunlight. These pollutants are emitted into the atmosphere by industrial facilities, electric power plants, and motor vehicles.

The second most important pollutant was PM2.5 (23% of days in 2017, sharply reduced from 2016). These tiny particles were not recognized as dangerous until relatively recently, though now they are thought to be the most deadly form of air pollution. I can’t find anything that says so specifically, but I believe the zero readings in 1983 and 1993 means that PM2.5 wasn’t being measured in Missouri, not that it wasn’t a significant pollutant back then. The EPA significantly tightened its regulations for PM2.5 in 2012. In 2015, no Missouri county was determined to be noncompliant with the new standards, however data gaps from sensors just across the Mississippi River prevented determination of whether pollution from Missouri was causing a violation of standards in the Illinois side of the metro area. Thus, the counties of Franklin, Jefferson, St. Charles, St. Louis, and St. Louis City were all called “unclassified.” Road vehicles, industrial emissions, power plants, and fires are important sources of PM2.5.

Sulphur dioxide used to be by far the most important pollutant. While it has not been eliminated and was still the most important pollutant on some days, good progress was made on reducing SO2 emissions: 6% of days in 2011. Since then, however, its relative importance has been on the increase, and in 2017 it was the most important pollutant on 16% of days. For a discussion of the role of SO2 in background air pollution, see this post. For my most recent update on the concentration of sulfur dioxide in background pollution, see here.

Don’t forget that Figure 1 does not show the levels of the six pollutants, it shows the percentage of days on which each was the most important. As previous posts have clearly shown, air quality is better. As we have reduced some types of air pollution, apparently, other types have increased in relative importance.

Missouri has come a long way in improving its air quality. To a large extent, it did so in two ways: by kicking some of its coal habit (replacing coal with natural gas and oil as sources of energy), and by requiring large coal-burning power plants to install pollution control equipment. We have more work to do, especially with regard to O3 and PM2.5, but it has been a significant environmental success story.

In the next post, I will discuss the health effects of air pollution. Spoiler alert: air pollution isn’t good for you!


Environmental Protection Agency. Air Quality Index Report. This is a data portal operated by the EPA. Data downloaded on 7/31/2018 from http://www.epa.gov/airdata/ad_rep_aqi.html.

Missouri Department of Natural Resources. Missouri State Implementation Plan: Infrastructure Elements for the 2012 Annual PM2.5 Standard. Viewed online 3/30/2017 at https://dnr.mo.gov/env/apcp/docs/adopted-isip-2012-pm2.5-naaqs.pdf.

Few Unhealthy Air Days in Missouri Counties in 2017

It is one thing to ask whether a county’s air quality is good, and another to ask if it is so bad that it is unhealthy. In the previous post, I reported on the percentage of days during which air quality was in the good range in 24 Missouri counties. This post focuses on the percentage of days with unhealthy air quality.

I looked at data from the EPA’s Air Quality Index Report for 24 Missouri counties. The data covered the years 2003-2017, plus the years 1983 and 1993 for a longer term perspective. For a fuller discussion of air quality and the data used for this post, and a map of the 24 counties, see my post Air Quality Update, 2017.

Figure 1. Data source: Environmental Protection Agency.

The EPA data distinguishes 4 levels of unhealthy air: Unhealthy for Sensitive Individuals, Unhealthy, Very Unhealthy, and Hazardous. No Missouri county was reported to have Very Unhealthy or Hazardous air quality for any of the years I studied. Figure 1 shows the percentage of monitored days for which air quality was either Unhealthy for Sensitive Individuals, or Unhealthy. The top chart shows a group of counties along the Mississippi River north or south of St. Louis. The middle chart shows a group of counties in the Kansas City-St. Joseph region. The bottom chart shows a group of widely dispersed counties outside of the other two areas. For the locations of the counties, see here.

(Click on chart for larger view).

The percentage of unhealthy air days was 1% or below for all Missouri counties . There were no unhealthy air days at all in 13 of the 24 counties, and no county had more than 4 unhealthy AQI days. Compared to 2016, 4 counties showed very small increases, and 9 had decreases. Compared to 1983, the total number of unhealthy air days across all counties decreased from 490 to 21, a 96% decline. St. Louis City, St. Louis County, Iron County, Jackson County, and Jackson County, in that order, were the counties in 1983 with the highest number of unhealthy air days. By 2017, those four counties had decreased the number of unhealthy air days by 98%, 99%, 97%, 100%, and 100%, respectively.

Well done! We have more work to do before all Missourians can breath truly good quality air every day, but the decrease in unhealthy days is amazing, just amazing. In the next post, I will discuss the most important air pollutants in Missouri. After that, I will discuss the health effects of air pollution, and you will understand why the reduction in unhealthy air days is such an important achievement.


Environmental Protection Agency. Air Quality Index Report. This is a data portal operated by the EPA. Data downloaded on 7/31/2018 from http://www.epa.gov/airdata/ad_rep_aqi.html.

Slightly Fewer Good Air Quality Days in 2017

Air quality in 9 out of 24 counties in Missouri improved in 2017 compared to 2016, while air quality in 14 declined. The data comes from the Air Quality Index Report maintained by the EPA , which contains data on the air quality of a number of Missouri counties going back to the early 1980s. For a fuller discussion of air quality and the data maintained by the EPA, or for a map of the counties, see my previous post.

Figure 1. Data source: Environmental Protection Agency.

Figure 1 at right show the percent of monitored days on which the Air Quality Index (AQI) was in the Good Range. The top graph is for a group of counties along the Mississippi River, the middle one is for a group of counties in the Kansas City-St. Joseph region, and the bottom one is for a widely scattered group of counties in neither of the other two groups. The charts represent every year from 2003-2017. In addition, they chart the data for 1983 and 1993 to give a long-term perspective.

(Click on figure for a larger view.)

Compared to 2016, the percentage of good air days increased in 9 out of the 24 counties. Most of the increases were small, but the percentage of good AQI days jumped by 32% in Stoddard County, by 23% in the Andrews County, by 19% in New Madrid County, and by 16% in the Jefferson County.

The percentage of good AQI days fell in 14 counties. In most cases the decline was small, In only Iron County was the decline as large as 10%.

Missouri’s 3 largest metropolitan areas, St. Louis, Kansas City, and Springfield had good air years in 2016, and counties associated with those cities all slipped in 2017.

In almost all Missouri counties the percentage of good air quality days was high in 2018. In no county was it below 60%, and it was 80% or above in 18 out of the 24 counties. As in previous years, the outstate group led in the percentage of good AQI days, which is expected because they don’t experience the concentration of pollution sources that large cities do.

In 2017, the City of St. Louis had the lowest percentage of good air days of any county in Missouri: 62%. St. Louis County had the second fewest, at 68%. In 1983, the percentage of good AQI days was 14% and 16% in those counties. St. Louis still has plenty of air quality challenges, but we’ve come a long way.

Clean air to breath should be everybody’s birthright. Looking at the chart, it is easy to see that over the long term, Missouri has greatly improved its air quality. It is just as easy to see, however, that we have more to do, especially in our large metropolitan areas.


Environmental Protection Agency. Air Quality Index Report. This is a data portal operated by the EPA. Data downloaded on 7/31/2017 from http://www.epa.gov/airdata/ad_rep_aqi.html.

Air Quality Update, 2017

I last looked at Missouri air quality data through the year 2016. This post begins a series to update the information through 2017. First will come an introduction to the Air Quality Index (AQI) criterion pollutants, then 2 posts on AQI trends over the years, then a post on which are the most important pollutants, and finally, a post on why air quality is important for human health.

Figure 1. The St. Louis Cathedral viewed from the Park Plaza on Black Tuesday (11/28/1939). Source: St. Louis Post-Dispatch.

Missouri has a notorious role in the annals of air quality, for 2 reasons. First, on November 28, 1939, a temperature inversion trapped pollutants in St. Louis; a thick cloud of dark smoke blanketed the city, blotting out the sun. The day came to be known as “Black Tuesday,” and it was one of the worst air quality events in recorded history. Figure 1 at right shows a view that day of the St. Louis Cathedral from (I think) the Park Plaza. More photos are available by searching on Google Images for “Black Tuesday St. Louis.” Second, St. Louis was one of 6 cities included in a 1993 study that conclusively showed a relationship between air pollution and mortality. St. Louis was the second most polluted city in that study. (Dockery et al, 1993)

Since then, many steps have been taken to reduce air pollution, and air quality has improved dramatically. Has the trend continued, or has the trend begun to backslide?

Since the 1980s the EPA has gathered air quality data from cities and counties in Missouri and maintained it in a national database. The following posts look at yearly data from 2003-2017. In addition, to give a longer term perspective, they include data for 1983 and 1993.

Figure 2. Counties for which the EPA reports air quality. Data source: Environmental Protection Agency.

The EPA data now includes 24 counties. In some of them, however, air quality has not been measured for the entire period. Figure 2 is map showing the locations of the 24 counties. They can be gathered into three groups: a group along the Mississippi River, a group in the Kansas City-St. Joseph Area, and a widely dispersed group that does not fall into either of the other two groups.

The EPA constructs an Air Quality Index (AQI) based on measurements of 6 criterion pollutants: particulates smaller than 2.5 micrometers particulates between 2.5 and 10 micrometers, ozone, carbon monoxide, nitrous oxide, and sulphur dioxide.

Particulates are tiny particles of matter that float around in the atmosphere. When we breathe, we inhale them, and if there are too many of them, they cause lung damage. There are 2 sizes: inhalable coarse particles have diameters between 2.5 and 10.0 micrometers, while fine particles have diameters less than 2.5 micrometers. How small is that? The diameter of a human hair is about 70 micrometers, so they are roughly 1/30 the width of a human hair. Figure 3 illustrates the size difference – these are really tiny particles. Recent evidence suggests that fine particles cause serious health problems; they get deep into the lungs, sometimes even getting into the bloodstream. (EPA 2015)

Figure 3. Size difference between human hair and PM2.5 particle.

Ozone is a highly corrosive form of oxygen. High in the atmosphere, we need ozone in order to absorb ultra-violet radiation. But at ground levels, it is corrosive to plants and animals, and too much of it can cause lung damage.

Sulphur dioxide smells like rotten eggs. Too much of it causes lung damage, and it also reacts with water vapor in the atmosphere to form sulphuric acid, one of the main ingredients of acid rain. A series of posts I wrote on background air pollution shows that background levels of sulphur dioxide have decreased over the last 30 years. However, concentrations of it can still build up and affect public health near emission sources.

Nitrous oxide is corrosive and reacts with ozone and sunlight to form smog. It is also one of the main causes of acid rain. Background levels in the atmosphere have decreased, but it, too, can build up locally near emission sources.

Perhaps the most important air pollutant of all, carbon dioxide, is not one of the criterion pollutants. It is not included in the AQI, and is not included in the discussion in the following posts. Carbon dioxide is the primary cause of climate change. I have written extensively on climate change in this blog, and interested readers can consult those posts by clicking on “Climate Change” at the top of the page or by looking for specific titles in the Table of Contents.

The biggest sources of air pollution are power plants, industrial facilities, and cars. These tend to concentrate in urban areas, but air quality can be a concern anywhere; some of Missouri’s air quality monitoring stations are located near rural lead smelters, for instance. Indeed, in my posts about the largest GHG emitting facilities in Missouri (here), I discovered that 7 out of 10 were located in rural areas.

In addition, weather plays an important role in air quality. On some days, weather patterns allow pollution to disperse, but on others they trap it, causing air quality to worsen. Hot, sunny summer days are of particular concern, although unhealthy air quality can happen any time. Black Tuesday was in November, after all.

The EPA has established maximum levels of each pollutant, and reports the number of days on which there are violations. The EPA also combines the pollutants into an overall Air Quality Index, or AQI, in order to represent the overall healthfulness of the air. The AQI is a number, but it does not have an obvious meaning. Suppose the median AQI is 75 – what does that mean? So the EPA has created six broad AQI ranges: Good, Moderate, Unhealthy for Sensitive Individuals, Unhealthy, Very Unhealthy, and Hazardous. The EPA reports a yearly AQI number and the number of days in which the AQI falls in each range.

In the following posts, I will update Missouri’s AQI, then the specific pollutants that seem to cause repeated problems.


Dockery, Douglas W., Arden Pope III, Xiping Xu, John D. Spengler, James H Ware, Martha E. Fay, Benjamin G Ferris, and Frank E. Speizer. 1993. “An Association Between Air Pollution and Mortality in Six U.S. Cities.” The New England Journal of Medicine, 329 (4), pp. 1753-1759.

Environmental Protection Agency. Air Quality Index Report. This is a data portal operated by the EPA. Data downloaded on 7/31/2017 from http://www.epa.gov/airdata/ad_rep_aqi.html.

Environmental Protection Agency. 2015. Particulate Matter: Basic Information. Viewed online 3/23/2017 at https://www.epa.gov/pm-pollution.

St. Louis Post-Dispatch. Look Back: Smoky St. Louis. This is a gallery of photos concerning the 1930s smog problem in St. Louis. Photo purchased online from http://stltoday.mycapture.com/mycapture/folder.asp?event=896392&CategoryID=23105.

Wikipedia. 1939 St. Louis Smog. Viewed 11/6/15 at https://en.wikipedia.org/wiki/1939_St._Louis_smog.

Good Days Are Better in Bryce Canyon, and Bad Days Are, Too

Figure 1. Air Pollution Affects Visibility at Bryce Canyon National Park. Source: National Park Service, 2017.

I began my last post with photographs taken in Bryce Canyon National Park on three days ranging from clear to hazy, shown again at right. Because it is one of the most remote locations in the continental USA, it is a good place to observe background air pollution.

(Click on photo for larger view.)

The haze in Bryce Canyon is caused by pollutants that have dispersed widely throughout the atmosphere. The previous post reviewed data on two pollutants that contribute the most to acid rain: sulfur dioxide and nitrogen dioxide.

Bryce Canyon, however, is most impacted by particulates, tiny particles that float freely in the air. They are too small to be seen individually with the naked eye, but collectively they cause haze. They also get into your lungs when you breathe, where they cause lung disease and other problems. The smallest ones (PM2.5) get most deeply into your lungs and are the greatest health hazard. How small are they? They are 2.5 microns or less in diameter, while the average human hair is 50-70 microns in diameter.

Figure 2. Source: IMPROVE Aerosol RHR (New Equation) Dataset.

I downloaded PM2.5 data from the Bryce Canyon IMPROVE Site. For each year, I selected the 10 highest readings and I averaged them. Then I selected the 10 lowest readings and I averaged them. The results are shown in the graph at right. The blue line represents the high readings, the red line the low readings.

Since 1983 the level of particulates on good days has trended slightly down.

In 1983 the bad days had roughly 5 times as much particulate matter in the air as the good days. The level of particulates on bad days trended up and peaked in 2009, about 20 years after data collection started. By then, the level had almost doubled, and the level of particulate matter on bad days was approximately 20 times the level on low days. Since then, the PM2.5 level has declined, and is now slightly lower than the level at which it started.

I don’t know what accounts for the reversal. My first guess would be the retirement of one or more coal-burning power plants, but searching the web does not seem to indicate it. The Navajo Generating Station, the largest in the West and the closest to Bryce Canyon, has been scheduled for retirement, but it has not occurred yet. It has been required to upgrade its pollution control equipment over the years, and perhaps that plays a role. It is also possible, however, that pollution from as far away as Las Vegas, Phoenix, or Southern California may have been involved. I just don’t know. If somebody out there does, please leave a comment and let us all know.

It was an issue of concern that the PM2.5 level on bad days continued to trend upward for so many years, and, whatever the cause, it is a relief to see that it has declined significantly. Hopefully it will decline even further from here.


IMPROVE Aerosol RHR (New Equation) Dataset, Database Query Wizard, Federal Land Manager Database, Interagency Monitoring of Protected Visual Environments (IMPROVE). http://views.cira.colostate.edu/web/DataWizard.

Source: Federal Land Manager Environmental Database. Database Query Wizard. Data downloaded 12/8/2017 from http://views.cira.colostate.edu/fed/DataWizard/Default.aspx.

Background Air Quality 2017

Several times this blog has reported on air pollution, especially focusing on the Air Quality Index published by the EPA. In general, air quality has improved significantly. (The most recent series starts here.) The Air Quality Index monitoring program in Missouri focuses on large metropolitan areas or potentially large sources of pollution. Monitoring sites are often located next to pollution sources such as busy highways, industrial areas, or smelters. The sites monitor pollution where it is most likely to be most intense, but they don’t tell us much about the background level of pollution that has dispersed into the atmosphere.

Air Pollution Affects Visibility at Bryce Canyon National Park. Source: National Park Service, 2017.

The photos at right show Bryce Canyon National Park on three days ranging from clear to hazy. Bryce Canyon is dry, so the haze is not caused by humidity, it is air pollution. But Bryce Canyon is one of the remotest locations in the continental United States. It is close to no cities and no major sources of air pollution. The haze is caused by pollution that has dispersed widely into the atmosphere.

Spurred by the problem of acid rain, in 1990 the Environmental Protection Agency, National Park Service, and Bureau of Land Management established a network of rural monitoring sites far from cities and significant sources of pollution, called the Clean Air Status and Trends Network (CASTNET). These cites monitor the degree to which pollutants have dispersed into the ambient air. CASTNET has grown into a national network of 95 monitoring sites. CASTNET focuses on only a few pollutants most relevant for acid rain: sulfur dioxide and sulfates, nitric acid and nitrates, and ozone. (Clean Air Status and Trends Network 2017a)

No CASTNET monitoring sites are located in Missouri. Sites are located in Clark County Arkansas, Champaign, DuPage, Jo Daviess, and Madison Counties in Illinois, Brown and Riley Counties in Kansas, and Adair County in Oklahoma. (Clean Air Status and Trends Network 2017b)

The program to reduce the air pollution that causes acid rain has been one of the most successful environmental programs in our nation’s history. Two of the principal causes of acid rain are sulfur dioxide and nitrogen dioxide. When these gases are emitted by power plants and vehicles, they mix with water vapor already present in the air to form sulfuric acid and nitric acid. Even in this diluted form, these powerful acids fall with the rain, killing plants and dissolving metal, stonework, and concrete. Forests are affected, of course, but in addition, billions of dollars of damage has been done to buildings, bridges and roads.

Figures 1-4 map the average background concentration of sulfur dioxide over 4 periods: 1989-1991, 1999-2001, 2009-2011, and 2011-2014. Figures 5-8 map the average background concentration of nitric acid over the same 4 periods. (Be sure to notice that there is a decade between the first three maps in each series, but fewer years between the final two.)

Suflfur Dioxide Maps

Figure 1. Source: CASTNET 2017a.

Figure 2. Source: CASTNET 2017a.









Figure 3. Source: CASTNET 2017a.

Figure 4. Source: CASTNET 2017a.











Nitric Acid Maps

Figure 5. Source: CASTNET 2017a.

Figure 6. Source: CASTNET 2017a.









Figure 7. Source: CASTNET 2017a.

Figure 8. Source: CASTNET 2017a.











First, notice that the white space on the maps disappears over time. The CASTNET system did not cover the whole country at first, and this represents the development of the system.

Second, notice that in 1989-1991, the area of high pollution concentration extended from roughly Missouri to the eastern and northeastern portions of the country. The prevailing wind blows west-to-east, blowing pollution from the Midwest to the East.

Third, notice that over time the areas of red and orange have disappeared, and the area of yellow has been much reduced. The background atmospheric concentration of these two pollutants is much less than it was in 1989.

The background level of sulfur dioxide has improved significantly in Missouri and across the entire eastern portion of the country. Across the West, it does not appear to have been very high when measurements started. On the other hand, across the West the high background concentration of nitric acid appears to have occurred primarily in Southern California. It has improved. So has the background concentration of nitric acid across Missouri and the entire eastern portion of the country.


Clean Air Status and Trends Network. 2017a. Ambient Air Concentrations. Downloaded 12/1/2017 from https://www3.epa.gov/castnet/maps/airconc.html.

Clean Air Status and Trends Network. 2017b. Clean Air Status and Trends Network (CASTNET): Program Overview. https://www3.epa.gov/castnet/docs/CASTNET-Factsheet-2015.pdf.

Clean Air Status and Trends Network. 2017c. Site Information, Clean Air Status and Trends Network, EPA, http://java.epa.gov/castnet/epa_jsp/sites.jsp.

National Park Service. 2017. Air Pollution Impacts, Bryce Canyon National Park. Downloaded 12/2/2017 from https://www.nature.nps.gov/air/Permits/aris/brca/impacts.cfm?tab=0#TabbedPanels1.

Green Buildings are Better – Health

Green buildings have better indoor environmental qualities, and deliver direct health benefits to those who work in them or live in them.

Americans spend an average of 90% of their time indoors. Indoor environments with low air circulation can concentrate pollutants 2 to 5 times higher than in outdoor air. Contaminants found in indoor air include organic compounds (e.g. formaldehyde, pesticide, fire retardant), microbes (e.g. bacteria, mold), inorganic gases (e.g. ozone, carbon monoxide, radon), and particulate matter (second-hand smoke, dust, smoke from fires).

Building-related illnesses include infections (e.g. Legionnaire’s disease), headache, nausea, nasal and chest congestion, wheezing, eye problems, sore throat, fatigue, chills and fever, muscle pain, neurological symptoms, and dry skin. That’s quite a list, and it should be apparent that indoor environmental quality is very important to health and well-being.

Green buildings have better indoor environmental qualities, and deliver direct health benefits to those who work in them or live in them, according to a review conducted in 2015. The review looked at 17 different studies of the relationship between green buildings and health. Green buildings had lower levels of volatile organic compounds, formaldehyde, allergens, nitrous oxide, smoke, and particulate matter.

The improved indoor environmental quality translated to improved self-reported health outcomes, and improved self-reported productivity. Only one study used objective health outcome metrics, but it is instructive. Thiel et al compared results at a children’s hospital in Pittsburgh before and after it moved from a non-green to a green facility. After the move, there was less employee turnover and open positions filled faster. Blood stream infection rates declined 70% and the number of corrections that had to be made to medical records declined 49%. Not only that, but patient mortality was expected to be 11% higher after the move, because the case load became more severe. However, the green hospital actually had a 19% decrease in patient mortality.

In a more traditional office setting, 263 employees were studied before and after they moved from a non-green building to a green one. After moving, they reported a 56% decrease in absences due to asthma and respiratory allergies, a 49% decrease in absences due to depression and stress, and an improvement in productivity (productivity was measured using an index that does not lend itself to a numerical comparison of before and after).

Thus, the data look promising for green buildings. At the same time, confounding factors could explain some of the improvements observed, and the fact that many studies used self-report data suggests that caution should be used in interpreting the studies. Studies using more objective data are needed.

What about the financial performance of green buildings? The next post will explore that.


Allen, Joseph, Piers MacNaughton, Jose Laurent, Skye Flanigan, Erika Eitland, and John Spengler. 2015. “Green Buildings and Health.” Current Environmental Health Report. Downloaded 7/9/2017 from https://link.springer.com/content/pdf/10.1007%2Fs40572-015-0063-y.pdf.

Singh, Amanjeet, Matt Syal, Sue Grady, and Sinem Korkmaz. 2010. “Effects of Green Buildings on Employee Health and Productivity.”

Thiel, C.L., Needy, K.L., Ries, R.J., Hupp, D., Bilec, M.M. (2014). “Building Design and Performance: A Comparative Longitudinal Assessment of a Children’s Hospital.” Building and the Environment. 78, August 2014, 130–136.
American Journal of Public Health. 1665-1668. Downloaded 7/9/2017 from https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2920980.

U.S. Institute of Medicine. 2007. Green Healthcare Institutions: Health, Environment, and Economics: Workshop Summary, Chapter 4. The Health Aspects of Green Buildings. National Academies Press. Viewed online 6/10/2017 at https://www.ncbi.nlm.nih.gov/books/NBK54149.

Invisible Pollution

You can’t always see air pollution in a photograph.

In the previous post I counted down the industrial facilities that are the 10 largest GHG emitters in Missouri, providing photos. Carbon dioxide, the main greenhouse gas, is colorless and odorless: you can’t see it. What, then, do the photos I posted show? Here are a few more photos and a discussion of what can and can’t be seen in them.

The Clean Air Act requires the EPA to set standards for atmospheric concentrations of 6 common air pollutants (aka criteria air pollutants). They are ozone, sulfur dioxide, nitrous oxide, carbon monoxide, and two classes of particulates: particulates less than 2.5 micrometers in size (PM2.5), and those between 2.5 and 10 micrometers (PM10). (See here.) They are by no means the only air pollutants emitted by large industrial plants. Among the 10 largest GHG emitters in Missouri, other pollutants include carbon dioxide (of course!) plus as many as 15-20 toxic compounds, most commonly heavy metals like lead and mercury (EPA TRI Explorer). Heavy metals are contained in coal and released when it is burned, and are toxic even in small amounts.

At least 5 of these pollutants are colorless gases: ozone, sulfur dioxide, nitrous oxide, carbon monoxide, and carbon dioxide. You can’t see them in the plume emitted by an industrial facility (or by your car, for that matter), they are invisible. The remaining compounds are contained in escaping particulates.

So, several of the pollutants can’t be readily seen in the plume of an industrial plant, but they are dangerous none-the-less. Generally, only escaping particulates are readily seen. Lets look at some examples:

(Click on photos for a larger view.)

Figure 1. The Sioux Energy Center Before Dawn on a Winter Day. Photo by John May.

Figure 1. The Sioux Energy Center Before Dawn on a Winter Day. Photo by John May.

Figure 2. Mississippi Lime Co. Ste. Genevieve Plant on a Winter Morning. Photo by John May.

Figure 2. Mississippi Lime Co. Ste. Genevieve Plant on a Winter Morning. Photo by John May.









Figure 1 and Figure 2 show the Sioux Energy Center and the Mississippi Lime Company Ste. Genevieve Plant. The photos show dramatic white plumes belching from the chimneys of these two plants. Those white plumes sure are dramatic, but they are not the problem. They are mostly steam – water vapor. It condenses when it hits the air on a cold morning, forming dramatic white clouds. The dark parts of the cloud are simply shadow where the cloud has become thick enough to block the sun.

The problem is what is hidden inside the white plume. That is where the air pollutants are. In addition, if you look at the buildings in Figure 2, you can see a gray haze. Those are particulates. I don’t know if they are PM2.5, PM10, or even larger particles, or perhaps a combination of all 3. While taking the photo in Figure 2, I noticed a definite rotten-egg smell. That is usually caused by sulfur dioxide, and it suggests that sulfur dioxide was being emitted by the plant. You can’t see it, however, it is colorless.

The Labadie Energy Center on a Spring Morning. Photo by John May.

Figure 3. The Labadie Energy Center on a Spring Morning. Photo by John May.

The Labadie Energy Center at Dawn on a Fall Morning. Photo by John May.

Figure 4. The Labadie Energy Center at Dawn on a Fall Morning. Photo by John May.









Figure 3 shows the Labadie Energy Center on a warm day in May. No billowing clouds of steam are visible, it wasn’t cold enough to condense them. With the naked eye you could barely make out a slight plume coming from the chimneys. By using a polarizing filter, I could make it just a bit more obvious. Here we have a photo of the real pollution being emitted by this power plant. I think it is probably fly ash – those PM2.5 and PM10 particles the EPA tracks. Figure 4 is a photo of the Labadie Energy Center on an October morning. If you look very hard, you can see a slight discoloration above the stacks, but man, is it hard to see! Unless the emissions are backlighted, or unless the photo is enhanced, it is very, very difficult to see the pollution that belches forth from these facilities.

Figure 4. The Thomas Hill Energy Center at Dusk on a Fall Day. Photo by John May.

Figure 5. The Thomas Hill Energy Center at Dusk on a Fall Day. Photo by John May.

Figure 6. The Hawthorn Plant on a Fall Day. Photo by John May.

Figure 6. The Hawthorn Plant on a Fall Day. Photo by John May.









Figure 5 shows the Thomas Hill Power Plant and Figure 6 shows the Hawthorne Plant. The plants were pumping out electricity, which means the boilers were burning, but no plume is visible above the chimneys. The conditions just weren’t right to be able to see it.

If you look at all the photos of power plants, you can see that they share one characteristic: a tall chimney. The one at New Madrid is 800 ft. tall, Iatan, Rush Island, and Labadie have stacks that are 700 ft. tall, Thomas Hill’s stack is 620 ft. tall, the Sioux Energy Center stack is 603 ft. tall, and so forth. Tall chimneys like this are expensive, so there is a reason for them. Most of the pollutants emitted out of the chimneys are poisonous. If they were emitted at ground level, they would blow with the wind and cause harm. In addition, almost all of them are regulated by the EPA. If the chimneys were less tall, there is a chance that the pollution could reach the ground at concentrations still high enough to put the plant in violation. By building very tall chimneys, the company ensures that by the time any of the pollutants reach the ground, they have been diluted sufficiently so that they don’t create a violation. If you look at the photo of the Mississippi Lime Co. Ste. Genevieve Plant, you can see that its chimneys are much shorter, and perhaps that is why I could smell the sulfur dioxide.

In one sense, this is a good strategy: people and property in close proximity aren’t exposed to high concentrations of the pollutants. In another sense, it is a bad strategy: it puts pollutants into the environment, where they accumulate and cause widespread damage. Thus, pollution from facilities here in the Midwest contributes to smog, acid rain, mercury accumulation in fish, and GHG build-up in the atmosphere.

Figure 7. The Labadie Energy Center Seen From Midtown St. Louis at Dusk on a Winter Day. Photo by John May.

Figure 7. The Labadie Energy Center Seen From Midtown St. Louis at Dusk on a Winter Day. Photo by John May.

One final photo: Figure 7 is a photo of the Labadie Energy Center taken on a winter day from the top of a building opposite Forest Park in St. Louis. Expand the photo and you can see the chimneys on the horizon. The plant is some 30 miles away from the camera. The plume rises more than 2,000 feet into the air before the steam evaporates. How much higher than that does the column of polluted hot air rise? I don’t know, but I would expect quite a bit. Even this visible plume dominates the otherwise empty sky and horizon.

These plants come with important economic benefits, which I reviewed in the first post of this series, and we couldn’t do without them. But their pollution is also a big deal.

So, the point is that you can’t necessarily see the pollution being emitted by a large industrial emitter. If the sun is in just the right spot, you might be able to barely make out some particulates. But the other pollutants are all invisible. On a cold day, the plant will emit billowing clouds of water vapor. Water vapor itself is mostly harmless, but it stands as a reminder of the invisible pollution hidden within.


Environmental Protection Agency. TRI Explorer, Release Facility Report. Data accessed 12/21/2016 at https://iaspub.epa.gov/triexplorer/tri_release.facility.

May, John. 2015. “Air Quality Update 2014.” Mogreenstats.com. Viewed online 12/21/2016 at https://mogreenstats.com/2015/11/06/air-quality-update-2014.

Wikipedia. List of Tallest Buildings in Missouri. Viewed online 12/21/2016 at https://en.wikipedia.org/wiki/List_of_tallest_buildings_in_Missouri#Missouri.27s_tallest_structures.

Summary of Missouri Air Quality in 2014

The last 4 posts have looked at air quality data for 20 Missouri counties for the years 2003-2014, plus 1983 and 1993 for a longer term perspective. They clearly show that Missouri has made dramatic progress in improving its air quality, but that more work remains to be done. This post summarizes the findings for 2014.

Fifteen out of twenty Missouri counties had no unhealthy air days in 2014. Most never had > 20% of unhealthy air days at any time covered by these statistics, only four did: St. Louis City, St. Louis County, Iron County, and Jefferson County. All four have cut the number to less than a quarter of its maximum value. The county with the highest percentage of unhealthy air days in 2014 was Jackson County, the location of Kansas City, at 14%. While that is a small fraction of total days, the trend is troubling, showing a persistent increase across the entire period (see chart in Few Unhealthy Air Days in Most Counties).

A soapbox moment:

I regard good air to breath as a basic human right. It goes right in there with “life, liberty, and the pursuit of happiness.” How can you live, be free, and pursue happiness if you don’t have good air to breathe? I very well understand that our air will never be pristine, for there are too many natural phenomena that put gases and particulates into it (like forest fires and wind-blown dust). But none of us should have to live with asthma or chronic lung disease simply because others of us pollute and refuse to clean up our act.

If one takes a very long term perspective, it must be acknowledged that air pollution was not monitored reliably prior to the 1980s. However, the photos from Black Tuesday in 1939 show that St. Louis, at least, has come a very long way indeed. That is very good news for us all. The success our nation has achieved improving local air quality and background air pollution offer hope that we can successfully address other important environmental problems, if only we will.

End of soapbox moment.


The data reviewed in this post comes from the previous four posts in this blog, Update on Missouri Air Quality, Air Quality Improves in 2013, Unhealthy Air Days Down from 2012, and Ozone and PM2.5 Are Our Most Important Air Pollutants

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