Ever paid attention to the black smoke rising out of the stack pipe of a transport truck? Caught that unmistakable hydrocarbon smell that goes along with it? Transportation of people and their goods is a major culprit for deteriorating the quality of our air. And it doesn鈥檛 stop there. A long list of other activities, such as heating our homes, electricity generation at power plants, agriculture, and construction of buildings and roads, contributes to ambient air pollution. Because of the wide range of activities responsible and the complex pathways between what is emitted and what we are exposed to, air pollution is a major challenge for environmental managers.

Why all the fuss over air pollution? Well, for a long time, the fields of toxicology and epidemiology have provided evidence that our health is negatively affected by air pollution. Exposure to ambient particulate matter (PM) and ozone carries risks of premature death and illness, both in the short and long-term. In Canada, evidence also exists that NO₂ is an important risk factor for death. Collectively, data from these fields are used to support environmental policies to protect public health. Policies have been developed that limit the levels of pollution in ambient air, such as the Canadian Ambient Air Quality Standards (CAAQS) for PM and ozone set by Environment Canada. Other policies that directly limit emissions at their source have also been set, such as vehicle emission standards that limit tailpipe emissions in Canada.

Imagine a world where we don鈥檛 need vehicle emission standards because cars don鈥檛 have tailpipes. Imagine a world where energy is renewable and non-polluting. Imagine a cleaner environment. It seems nearly impossible to achieve, right? Well, it may not be as far away as we think. Emissions of pollutants in North America have been on the decline over the past few decades thanks to stricter environmental policies. Take, for example, NO_x emissions [nitrogen oxide (NO) + nitrogen dioxide (NO₂)] produced in combustion of fuels, such as from power plants or motor vehicles. NO_x undergoes changes in the atmosphere before affecting the air we breathe and has the potential to form PM. NO_x is also a major contributor to NO₂ and ozone (O₃) in the air we breathe 鈥� both powerful oxidants in the human body. Since 1990, according to Environment Canada, Canada鈥檚 NO_x emissions have declined roughly 28% as a result of policies to clean exhaust from vehicles and power plants. The result has been a steady decline in ozone and NO₂ and an overall improvement in air quality.

Clearly, if exposure to air pollution affects our health, then as policies become stricter, the health of Canadians benefits. But just how much does society benefit? And how far should policies go before they are sufficient?
Last year, our research team at 杏吧原创 University sought to answer these questions. Our findings challenged a fundamental and long-held view in environmental economics 鈥� the law of diminishing returns. According to this law, we should strive only to reduce our emissions by so much, because the benefit of further efforts to reduce emissions diminishes the more and more we reduce. At some point, our efforts to achieve better air quality no longer make sense financially: it costs more to clean the air than it benefits society. But in a study published in 2015, we instead found quite the opposite: the cleaner the air gets, the larger the benefit of reducing our emissions a little bit more. In other words, the less and less we emit, the more effective the next ton of emission control is at reducing ozone pollution. For more, see the blog on

So why do our findings differ from the conventional view? Atmospheric chemistry dictates compounding benefits for pollutants like ozone that are formed through chemical reactions rather than being emitted directly. It tells us how things move and transform in the atmosphere up to the point where we are exposed. But there is another part to this story. How does the human body respond to pollution it is exposed to? Does the body鈥檚 response argue for compounding benefits or diminishing returns?

Characterizing the dose-response curve between pollutants like PM or NO₂ and mortality gives us insight into these questions. Epidemiologists have believed for a long time that the dose-response relationship between exposure and mortality is linear. In other words, in an already pristine environment, making the air a little bit cleaner yields the same reduction in risk as if we cleaned a dirty environment by the same amount. We would get the same benefits to health regardless of how clean the air is initially, as long as we clean it by a comparable amount. But with large cohorts tracking millions of people and their health status over time, epidemiologists now have the power to better delineate the true dose-response relationship. And more and more, studies are finding that the assumed linear relationship may just not be the case. Studies in Canada, such as the Canadian Census, Environment, and Health Cohort (CanCHEC) study have instead found non-linear dose-response relationships for the pollutants NO₂ and PM and mortality. This alternative form of dose-response curve implies that people become more sensitive to pollution as the air becomes cleaner. Or alternatively, if we continue cleaning the atmosphere by progressively reducing our emissions, we get larger and larger reductions in health risks for each small improvement in air quality. The next unit of improved air quality yields more benefit than the previous unit. Sound familiar?

In a newer research project, we worked collaboratively with experts at Health Canada to examine the policy implications of this newer, non-linear form of dose-response relationship. We linked data from CanCHEC with engineered models that track the movement and transformation of air pollutants in the atmosphere from the time they are emitted. The result? A comprehensive set of information that gives insight into how the health of Canadians is directly affected by pollution emitted at its source, whether from the tailpipe of a car or the stack of a power plant.

Our findings indicate that reducing emissions of NO_x brings health benefits of up to $1,400,000 per ton of emission. Where does this benefit come from? When we reduce NO_x, NO₂ in ambient air immediately decreases, and NO₂ is linked to death. But this is just part of the story. With the new, non-linear dose-response model found in CanCHEC, the benefits of reducing emissions increase dramatically as policies become more stringent. With Canada-wide reductions in emissions from all sources, the benefits of reducing each additional ton of emission can grow by 3 or more times. And the benefits are, more often than not, larger than what we would have predicted based on the traditional, linear dose-response curve.

In light of these increasing benefits, we might wonder how much it actually costs to reduce emissions. We have to change our technologies, and even our behaviours, to bring about these changes. So what is the price tag? Well, the answer may not be straightforward. Such costs vary with the type of source (such as vehicles and power plants), and even more so from one place to another. But, on average, the cost of reducing 1 ton of NO_x from industrial stacks can be anywhere from a few hundred dollars to a few thousand. And the costs of reducing the next ton will rise nonlinearly with stricter and stricter policies.

So, is it worth paying? Even without precise estimates of these costs, benefits clearly outweigh the costs by at least an order of magnitude. And even if costs rise as we move towards a cleaner environment, so do the benefits. It鈥檚 a race between benefits and costs and the point at which one catches the other may be much farther away than we thought previously.

The intersection of atmospheric science, epidemiology, and economics is a rapidly advancing niche of research. And one thing is clear: whether you approach this problem from an atmospheric science angle or an epidemiology one, we are finding that we ought to be doing more to emit less. Our policies ought to be stricter. We ought to take better control of our environment and our health.

Key references:

Pappin AJ, Mesbah SM, Hakami A, Schott S. 2015. Diminishing returns or compounding benefits of air pollution control? The case of NO_x and ozone. Environ Sci Technol. 49(16):9548-9556.

Pappin AJ, Hakami A, Blagden P, Nasari M, Szyszkowicz M, Burnett RT. The impact of a nonlinear concentration-response function in estimating the benefits of emissions abatement. Environ Res Lett. Under review.

By Marie-Claire Flores Pajot, Dept. of Health Sciences, 杏吧原创 University

No child should be left out from going to school for the very first time, playing at recess with new friends, or having the opportunity to learn about what the world will offer them in life. And no family should lose these or other precious moments with their children. Unfortunately, this is the case for some. Planning visits to the oncologist as opposed to birthday parties; cheering as they see their brave children succeed a battle through chemotherapy as opposed to cheering for scoring a goal in a soccer game.

Estimates from the Canadian Cancer Society in 2014 indicate that in the next few years approximately 1450 new cases of cancer will occur annually in Canadian children under the age of 19. Thankfully, many childhood cancers can now be treated and even cured. However, treatment does not remediate the significant psychosocial and financial burden to patients and families; not to mention the dreadful journey through chemotherapy: pain, emotional distress and sleepless nights for both the young patient, and their families.

It is often forgotten that overcoming treatment is not crossing the finish line; unfortunately, quite often the battle continues. Late-effects are common and can accompany survivors for months or even decades after their cancer treatment has ended. Some of the late-effects can be emotional complications, such as anxiety and depression; other late-effects are reproductive or sexual development problems, that can affect both boys and girls well into adulthood; learning and memory difficulties are also common; and there are many physical complications such as heart problems caused by the use of anthracycline drugs during treatment, hearing problems due to radiation therapy, as well as muscle and nerve damage that can result in pain or weakness (National Cancer Institute, 2015).

New advances are aiming for early diagnosis to improve patient outcomes (Weller et al., 2012). The causes of the different cancers are complex and elusive but continue to be investigated in clinical settings, laboratories and epidemiological studies (Danaei et al., 2005). Nonetheless, there is likely a combination of genetics, lifestyle, environment and random error in cell replication and control, which influence an individual’s cancer risk (Buka, Koranteng, & Vargas, 2007; Stiller, 2004). In order to implement cancer prevention initiatives, it is important to better understand how many of the new cancer cases in a population are due to modifiable risk factors that could be prevented.

The role of the environment
The importance of our environment has been recognized to play an important role in our physical and mental health (Evans, 2003; McMorris, Villeneuve, Su, & Jerrett, 2015). Yet, we often forget that even the filtered water used for the morning coffee or tea, the background noise, the air conditioning at the office, all impacts our overall wellbeing to some degree. The significant implication of our environment shaping our health has motivated researchers to investigate possible causes to cancer at different spatial scales, from the particles that linger in our bedroom (Zhang & Smith, 2003), to the neighbourhood we live in (Eschbach, Mahnken, & Goodwin, 2005).

Environmentally derived chemicals entering the human body via food, drink or air that have been shown to, or suspected to, increase risk of developing cancer are called 鈥榚nvironmental carcinogens鈥� (Hemminki, 1990). To date, some of the well-studied environmental carcinogens include electromagnetic fields, pesticides, and air pollution (Cancer; Zahm & Devesa, 1995). Canadian studies that have looked at recognized carcinogens emitted to the environment, found that the amounts varied considerably by province. Interestingly, the rate of new adult cancer cases is also observed to vary by province, with a declining rates moving across Canada from east to west, with the highest incidence rates in Quebec and the Atlantic provinces and the lowest rates in Alberta and BC (Canadian Cancer Society鈥檚 Advisory Committee on Cancer Statistics, 2015). These differences in incidence rates of cancer by geographic location can be driven by multiple factors, most notably differences in the age demographic of those who live in different locations. However, neither demographic differences nor lifestyle-related factors, like smoking, can fully explain these geographic variations. Exposure to environmental carcinogens has been recognized to have a significant impact on new cancer rates, and due to the observed patterns of variability of exposure across the nation, studying the extent to which these patterns co-occur with childhood cancer rates may give insight into the etiology of some cancers.

These questions have motivated researchers Drs. Alvaro Osornio-Vargas, Osmar Zaiane, David Eisenstat from the University of Alberta, and Paul Villeneuve from 杏吧原创 University, to take a further step and investigate the associations between exposure to environmental carcinogens and the incidence of childhood cancer in Canada. This study is being funded by the聽 and . Using a special technique called data mining, they will study the national patterns and trends of childhood cancer and assess the relationship with multiple chemicals. Nineteen known carcinogens and 51 potential carcinogens emitted into the air by industries between 2001 and 2011 will be studied to better understand their association with cancer in children under the age of 19 years. The International Agency for Research on Cancer (IARC) classifies outdoor air pollution as a carcinogen (Simon, 2013). In urban areas, traffic is often the main source of ambient air pollution and there are increasing reports of the risks associated with proximity to high-density traffic, including risk of childhood leukemia (Raaschou-Nielsen, Hertel, Thomsen, & Olsen, 2001). Therefore, in addition to industrial emissions, this project will also examine impacts of meteorological conditions that play a role in dispersing emissions, as well as the impact of proximity to major roads.

Overall, this study hopes to improve our understanding of the extent to which the geographic variability of childhood cancer rates in Canada is associated with industrial and traffic-related pollution. The knowledge gained might support future prevention strategies for specific types of cancer. More epidemiological studies, such as this one, in conjunction with clinical studies, will identify areas where action can be taken to prevent childhood cancer, and perhaps one day children will not have to choose between which toy to bring to chemo, but instead which park to play in next.

References
Buka, I., Koranteng, S., & Vargas, A. R. O. (2007). Trends in childhood cancer incidence: review of environmental linkages. Pediatric Clinics of North America, 54(1), 177-203.

Canadian Cancer Society鈥檚 Advisory Committee on Cancer Statistics. (2015). Canadian Cancer Statistics 2015. Canadian Cancer Society.

Cancer, I. A. f. R. o. Overall Evaluations of Carcinogenicity to Humans. List of all agents, mixtures and exposures evaluated to date.

Danaei, G., Vander Hoorn, S., Lopez, A. D., Murray, C. J., Ezzati, M., & group, C. R. A. c. (2005). Causes of cancer in the world: comparative risk assessment of nine behavioural and environmental risk factors. The Lancet, 366(9499), 1784-1793.

Eschbach, K., Mahnken, J. D., & Goodwin, J. S. (2005). Neighborhood composition and incidence of cancer among Hispanics in the United States. Cancer, 103(5), 1036-1044.

Evans, G. W. (2003). The built environment and mental health. Journal of Urban Health, 80(4), 536-555.

Hemminki, K. (1990). Environmental carcinogens Chemical Carcinogenesis and Mutagenesis I (pp. 33-61): Springer.

McMorris, O., Villeneuve, P. J., Su, J., & Jerrett, M. (2015). Urban greenness and physical activity in a national survey of Canadians. Environmental research, 137, 94-100.

National Cancer Institute. (2015). Late Effects of Treatment for Childhood Cancer. Childhood Cancers.

Raaschou-Nielsen, O., Hertel, O., Thomsen, B. L., & Olsen, J. H. (2001). Air pollution from traffic at the residence of children with cancer. American journal of epidemiology, 153(5), 433-443.

Simon, S. (2013). World Health Organization: Outdoor Air Pollution Causes Cancer. American Cancer Society.

Stiller, C. A. (2004). Epidemiology and genetics of childhood cancer. Oncogene, 23(38), 6429-6444.

Weller, D., Vedsted, P., Rubin, G., Walter, F., Emery, J., Scott, S., . . . Olesen, F. (2012). The Aarhus statement: improving design and reporting of studies on early cancer diagnosis. British Journal of Cancer, 106(7), 1262-1267.

Zahm, S. H., & Devesa, S. S. (1995). Childhood cancer: overview of incidence trends and environmental carcinogens. Environmental health perspectives, 103(Suppl 6), 177.

Zhang, J. J., & Smith, K. R. (2003). Indoor air pollution: a global health concern. British medical bulletin, 68(1), 209-225.

By Amanda Pappin, Dept. of Civil and Environmental Engineering, 杏吧原创 University.

We have all experienced the law of diminishing returns. It shows up in various scientific disciplines and in our everyday lives. Weight loss is one example that often comes to mind. If you cut your food intake by a fixed amount, initially weight comes off quickly. But with each pound that disappears from the scale, it seems that you have to work even harder to lose the next. Your diet hasn鈥檛 changed, and other factors like exercise are the same as before, but that scale just isn鈥檛 budging. Frustrating, right?

Well, the law of diminishing returns also applies to various topics in economics. At least that鈥檚 what we thought was the case for air pollution economics.

Air pollution poses a significant challenge to environmental managers because what is emitted from the tailpipe of a car, or the stack of an industrial facility, can undergo profound changes in the atmosphere before affecting the air we breathe. Some of the major pollutants that pose risks to our health are not emitted directly, but rather formed in the atmosphere through complex physical and chemical processes. These include pollutants that we often hear about, such as ozone or small airborne particles (particulate matter or PM). Epidemiologists have shown that both pollutants affect human health and increase our risks of illness and even death.

For a long time, economists who study air pollution have believed that the societal payback of reducing pollutant emissions is a battle against diminishing returns. Cleaning up polluted air brings large benefits to our health and the environment. Cleaning up less polluted air by the same amount yields much smaller benefits. Economists have argued that the environment has a natural ability to cleanse itself of pollution 鈥� an ability that works best when pollution is at low levels. As the air becomes more polluted, the environment becomes overwhelmed and cannot remove added pollution as effectively.

My colleagues and I at 杏吧原创 University have tested the validity of the theory of diminishing returns as it relates to air pollution. For the first time, we attached numbers to the benefits of reducing emissions to see how they change as we strive to emit less pollution. Our work, just published in the , sheds new light on the topic.

We used a numerical air quality model, infused with epidemiological and economic data, to estimate the benefits of reducing emissions on a per-ton basis. We defined 鈥渂enefits鈥� as the number of deaths avoided in the population because of reduced ozone, which we converted to dollar values. We focused on the benefits of reducing emissions of nitrogen oxides (NO_x), which are major players in formation of ground-level ozone. NO_x is emitted from motor vehicles and industrial facilities when air comes into contact with high temperatures in fuel combustion.

Our objective was to test whether the per-ton benefits of reducing NO_x emissions decline over time, as environmental economists have suggested. And we found just the opposite. We showed that instead, benefits increase substantially as we continue to emit less. In other words, each additional ton of NO_x emission reduction becomes more beneficial than the previous ton. While looking for diminishing returns, we instead found compounding benefits!

Los Angeles smog

We found that, on average in the U.S., reducing NO_x from vehicles yields benefits of $13,000 per ton of NO_x. On an average per-vehicle basis, the price tag of NO_x emissions can be as high as $870 per year. This number varies depending on where the vehicle is driven, with benefits tending to be larger around populous urban areas than in the countryside. What about diminishing returns? On average, the benefits of reducing NO_x emissions would almost double if we reduce emissions across the country by 60%. Further, if we reached a level of zero man-made emissions, this benefit would quadruple, on average, yielding benefits of $51,000 per ton. The 4-fold average increase in benefits means that adjusting our way of life not only benefits society now, but will also bring benefits for the future. Every dollar that we spend to clean up our air makes the next dollar invested even more valuable.

So why do our findings disagree with the conventional view of diminishing returns in economics? It comes down to a lack of data, resources, and models to assess the adequacy of the theory in question. Only recently have engineers and atmospheric scientists used their comprehensive numerical models for economic applications. And those who have done so had not fully explored the assumptions used in this theory.

To an atmospheric chemist or air pollution scientist, the idea of diminishing returns in air pollution is counterintuitive for pollutants like ozone. Ozone is formed through photochemical reactions in the atmosphere, and its formation depends on how much NO_x and other pollutants are emitted. In polluted air, each emitted NO_x molecule has to compete with many others to form ozone. As the air becomes cleaner, and NO_x less abundant, these molecules are in higher demand. It is for this reason that our results come as little surprise to researchers in atmospheric chemistry and air pollution. But for economists, our findings are surprising, and frankly, a bit bizarre.

A challenge facing environmental managers is that while cleaning the air entails indisputable health and environmental benefits, doing so also costs money. Not only does it cost money, the cost increases as we emit less and less, and at some point, surpasses the expected societal benefits. Economists argue that it is to society鈥檚 benefit for environmental policies to progress to the point of equilibrium where incremental benefits equal costs, and no further. The question of whether benefits diminish or compound is one of great importance to finding this target level of emission reduction. Under the long-held view of diminishing returns, there is less incentive to keep reducing emissions, and the point of equilibrium is closer to our current habits. Our findings offer a new perspective. Compounding benefits provide further incentive to reduce emissions, and to keep reducing, towards an equilibrium point further down the policy trajectory.

So while you opt more and more to commute by bike or by foot to achieve that next pound of weight loss, know that society will increasingly benefit as you do.

This blog is based on:

Stream image courtesy of Evgeni Dinev at FreeDigitalPhotos.net