Both climate change and poor air quality result primarily from the combustion of fossil fuels, and it is within urban areas that these intertwined issues are most acute. The International Energy Agency (IEA) estimated that urban areas are responsible for more than 70% of all energy related fossil fuel emissions, and this share is expected to grow as people continue to migrate into urban areas. Similarly, the United Nations Environment Program (UNEP) estimates that urban air pollution is linked to 1 million premature deaths and 1 million prenatal deaths each year, costing 2% of GDP in developed countries and 5% GDP in developing countries, and the World Health Organization (WHO) recently noted that urban air quality is deteriorating. Addressing air quality and climate change impacts will bring economic benefits, but there is still much that can be learned about how best to take care of these issues in terms of both cost and efficacy.
One of the central challenges in air quality research is evaluating the effect of regulatory action on human health impacts because assessing this involves multiple diverse scientific fields. The Health Effects Institute (HEI) links the various fields of air quality research using what it calls the “chain of accountability,” described as: regulatory action to emissions to ambient air quality to exposure/dose to human health. It has long been known that pollutants such as ozone and particulate matter (PM) can cause a range of respiratory and cardiovascular problems, but in order to understand how regulatory action will impact human health outcomes, researchers need to know the spatial and temporal pattern of emissions, the physical mixing and chemical reactions occurring in the air across complex urban landscapes, and the time and duration a person is outside. Although indoor air quality is generally much better in developed countries, it is a major problem in developing countries. The EPA uses the best estimates of these factors available at the time to set air pollution standards, but as understanding of them improves, the standards often need to be revised. A revision of this nature is currently underway to lower the national air quality standard for ground level ozone. The crux in improving our ability to better connect regulations with human health outcomes—and also their cost effectiveness—therefore lies in making improvements along the entire chain of accountability.
Routine monitoring of ambient air quality traditionally occurs at widely-spaced fixed locations. These long term measurement sites provide good coverage over time, but have limited fine-scale spatial coverage. “Mobile labs” based out of vehicles or airplanes can provide excellent fine-scale spatial coverage, but they have high operational costs and their duration is short. To address these monitoring challenges, researchers at the University of Utah recently initiated a new project to monitor air quality and greenhouse gas concentrations using instruments installed on an light rail car (known as “TRAX”) operated by the Utah Transportation Authority (UTA) in Salt Lake City, Utah. The train traverses the city on the same course throughout each day, collecting data about both the spatial and temporal patterns of air pollutants and greenhouse gases. Since the train is electrified, there are no direct emissions from the train itself to obscure the measurements, and because the train is already running as part of the public transit system, there are no additional costs to using the train to collect data. Light rail trains with air quality measurements have been instrumented with success in a couple of European cities, but the TRAX experiment appears to be the first of its kind in the United States.
The pilot phase of the project was conducted in August, 2014, and lasted one month, measuring ozone, methane, and carbon dioxide. This yielded such interesting results that a longer term installation was immediately pursued. Siemens, the company that manufactures the TRAX light rail cars, donated a specialized metal container to the project, in which instruments were installed on top of a train car. This next phase began operations on December 8th, 2014, and for the winter season the ozone monitor was swapped out for instruments that measure particulate matter that is the dominant air pollutant locally in the winter. Modems were also installed to acquire the data in real time and display it on the web so that both researchers and the public can observe current air quality conditions in Salt Lake City.
While this project is in its infancy and the data are preliminary, it is generating a lot of interest. Salt Lake City is nestled in a valley between the Oquirrh and Wasatch mountain ranges, just southeast of the Great Salt Lake. This mountainous setting is an outdoor recreation hotspot, but it also presents unique air quality challenges. During the winter there are frequent “inversions,” which create a stable air mass close to the ground and act like a lid on the valley so that any pollutants emitted in the valley are trapped there, building up to unhealthy levels if inversion conditions persist for more than a few days. One of the TRAX routes extends across the valley such that during an inversion event in early January, the train emerged out of the top of the inversion and sampled relatively clean air on both sides of the valley. People living at a higher elevation on the valley benches had much cleaner air than people living near the topographic bottom of the valley on that day. However, the elevation of the inversion layer was observed to be much higher on other days, leading to no difference in air quality between the valley floor and the benches. Weather conditions can greatly affect the levels and distribution of pollutants around the valley such that parts of the valley can remain polluted while others are not.
The take home message from the data measured using this new mobile platform is that ambient air quality varies significantly across time and space, reflecting pollutant emissions and wind patterns that vary from day to day, and hour to hour. But it is possible to observe some of these variations with the new train mounted sensors. Observations such as these may help fill in some of the gaps evident in the air quality chain of accountability for the Salt Lake Valley. The data being collected could be combined with weather and chemistry computer models to generate fine-grained views of pollutant distributions, thereby improving estimates of individual exposure, which health researchers may be able to use to study the impacts on human health. At the same time, these observations may also be able to shed additional light on emission hotspots and inform regulators how their regulatory actions are performing. As the connections between policy actions and human health become more robust, the cost savings of reduced emergency room visits, reduced asthma, and other negative health outcomes could be quantified and related to future policy proposals.
It is important to note that this project is not meant to replace existing air quality monitors. Because of the constraints inherent to a mobile deployment such as limited space and robustness, the instruments are not as precise or accurate as the ones operated by the Department of Air Quality. Furthermore, since this project is in its infancy, there is a substantial amount of data validation and peer review that needs to occur before these measurements are considered robust. This work is just beginning, but the initial results are promising.
Greenhouse gases have a similar chain of accountability, but instead of emissions affecting local air quality, they contribute to climate change. Just as in the case of air quality, the same methodological improvements provided by the TRAX observations could lead to improved understanding of fine-scale variations in greenhouse gas concentrations through the city, addressing questions about how societal behavior and urban development affect greenhouse gas emissions. This type of work could become an important component of the newly announced efforts by the EPA to monitor, report, and verify methane emissions that can leak from natural gas infrastructure or be emitted from landfills. This understanding could also feed back into the chain of accountability and could help us understand the most cost effective ways to mitigate emissions and reduce the urban carbon footprint. Ultimately, since air pollutants are often co-emitted with greenhouse gases, any policies aimed at improving air quality will also reduce human contributions to climate change. The co-benefits of improved air quality is likely one of the reasons for the recent historic agreement between the US and China to mitigate greenhouse gas emissions.
Since emissions in cities contribute disproportionately to both poor air quality and climate change, improvements in our ability to observe and understand emissions using innovative observational tools such as the TRAX platform may help us address emissions in a way that minimizes cost and maximizes efficacy.
Logan Mitchell, Ph.D. is a Postdoctoral Research Scientist in the Land-Atmosphere Interactions Research Group in the Atmospheric Sciences Department at the University of Utah.
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Public Transit Boosting Research on Air Quality and Climate Change
March 23, 2015
Both climate change and poor air quality result primarily from the combustion of fossil fuels, and it is within urban areas that these intertwined issues are most acute. The International Energy Agency (IEA) estimated that urban areas are responsible for more than 70% of all energy related fossil fuel emissions, and this share is expected to grow as people continue to migrate into urban areas. Similarly, the United Nations Environment Program (UNEP) estimates that urban air pollution is linked to 1 million premature deaths and 1 million prenatal deaths each year, costing 2% of GDP in developed countries and 5% GDP in developing countries, and the World Health Organization (WHO) recently noted that urban air quality is deteriorating. Addressing air quality and climate change impacts will bring economic benefits, but there is still much that can be learned about how best to take care of these issues in terms of both cost and efficacy.
One of the central challenges in air quality research is evaluating the effect of regulatory action on human health impacts because assessing this involves multiple diverse scientific fields. The Health Effects Institute (HEI) links the various fields of air quality research using what it calls the “chain of accountability,” described as: regulatory action to emissions to ambient air quality to exposure/dose to human health. It has long been known that pollutants such as ozone and particulate matter (PM) can cause a range of respiratory and cardiovascular problems, but in order to understand how regulatory action will impact human health outcomes, researchers need to know the spatial and temporal pattern of emissions, the physical mixing and chemical reactions occurring in the air across complex urban landscapes, and the time and duration a person is outside. Although indoor air quality is generally much better in developed countries, it is a major problem in developing countries. The EPA uses the best estimates of these factors available at the time to set air pollution standards, but as understanding of them improves, the standards often need to be revised. A revision of this nature is currently underway to lower the national air quality standard for ground level ozone. The crux in improving our ability to better connect regulations with human health outcomes—and also their cost effectiveness—therefore lies in making improvements along the entire chain of accountability.
Routine monitoring of ambient air quality traditionally occurs at widely-spaced fixed locations. These long term measurement sites provide good coverage over time, but have limited fine-scale spatial coverage. “Mobile labs” based out of vehicles or airplanes can provide excellent fine-scale spatial coverage, but they have high operational costs and their duration is short. To address these monitoring challenges, researchers at the University of Utah recently initiated a new project to monitor air quality and greenhouse gas concentrations using instruments installed on an light rail car (known as “TRAX”) operated by the Utah Transportation Authority (UTA) in Salt Lake City, Utah. The train traverses the city on the same course throughout each day, collecting data about both the spatial and temporal patterns of air pollutants and greenhouse gases. Since the train is electrified, there are no direct emissions from the train itself to obscure the measurements, and because the train is already running as part of the public transit system, there are no additional costs to using the train to collect data. Light rail trains with air quality measurements have been instrumented with success in a couple of European cities, but the TRAX experiment appears to be the first of its kind in the United States.
The pilot phase of the project was conducted in August, 2014, and lasted one month, measuring ozone, methane, and carbon dioxide. This yielded such interesting results that a longer term installation was immediately pursued. Siemens, the company that manufactures the TRAX light rail cars, donated a specialized metal container to the project, in which instruments were installed on top of a train car. This next phase began operations on December 8th, 2014, and for the winter season the ozone monitor was swapped out for instruments that measure particulate matter that is the dominant air pollutant locally in the winter. Modems were also installed to acquire the data in real time and display it on the web so that both researchers and the public can observe current air quality conditions in Salt Lake City.
While this project is in its infancy and the data are preliminary, it is generating a lot of interest. Salt Lake City is nestled in a valley between the Oquirrh and Wasatch mountain ranges, just southeast of the Great Salt Lake. This mountainous setting is an outdoor recreation hotspot, but it also presents unique air quality challenges. During the winter there are frequent “inversions,” which create a stable air mass close to the ground and act like a lid on the valley so that any pollutants emitted in the valley are trapped there, building up to unhealthy levels if inversion conditions persist for more than a few days. One of the TRAX routes extends across the valley such that during an inversion event in early January, the train emerged out of the top of the inversion and sampled relatively clean air on both sides of the valley. People living at a higher elevation on the valley benches had much cleaner air than people living near the topographic bottom of the valley on that day. However, the elevation of the inversion layer was observed to be much higher on other days, leading to no difference in air quality between the valley floor and the benches. Weather conditions can greatly affect the levels and distribution of pollutants around the valley such that parts of the valley can remain polluted while others are not.
The take home message from the data measured using this new mobile platform is that ambient air quality varies significantly across time and space, reflecting pollutant emissions and wind patterns that vary from day to day, and hour to hour. But it is possible to observe some of these variations with the new train mounted sensors. Observations such as these may help fill in some of the gaps evident in the air quality chain of accountability for the Salt Lake Valley. The data being collected could be combined with weather and chemistry computer models to generate fine-grained views of pollutant distributions, thereby improving estimates of individual exposure, which health researchers may be able to use to study the impacts on human health. At the same time, these observations may also be able to shed additional light on emission hotspots and inform regulators how their regulatory actions are performing. As the connections between policy actions and human health become more robust, the cost savings of reduced emergency room visits, reduced asthma, and other negative health outcomes could be quantified and related to future policy proposals.
It is important to note that this project is not meant to replace existing air quality monitors. Because of the constraints inherent to a mobile deployment such as limited space and robustness, the instruments are not as precise or accurate as the ones operated by the Department of Air Quality. Furthermore, since this project is in its infancy, there is a substantial amount of data validation and peer review that needs to occur before these measurements are considered robust. This work is just beginning, but the initial results are promising.
Greenhouse gases have a similar chain of accountability, but instead of emissions affecting local air quality, they contribute to climate change. Just as in the case of air quality, the same methodological improvements provided by the TRAX observations could lead to improved understanding of fine-scale variations in greenhouse gas concentrations through the city, addressing questions about how societal behavior and urban development affect greenhouse gas emissions. This type of work could become an important component of the newly announced efforts by the EPA to monitor, report, and verify methane emissions that can leak from natural gas infrastructure or be emitted from landfills. This understanding could also feed back into the chain of accountability and could help us understand the most cost effective ways to mitigate emissions and reduce the urban carbon footprint. Ultimately, since air pollutants are often co-emitted with greenhouse gases, any policies aimed at improving air quality will also reduce human contributions to climate change. The co-benefits of improved air quality is likely one of the reasons for the recent historic agreement between the US and China to mitigate greenhouse gas emissions.
Since emissions in cities contribute disproportionately to both poor air quality and climate change, improvements in our ability to observe and understand emissions using innovative observational tools such as the TRAX platform may help us address emissions in a way that minimizes cost and maximizes efficacy.
Logan Mitchell, Ph.D. is a Postdoctoral Research Scientist in the Land-Atmosphere Interactions Research Group in the Atmospheric Sciences Department at the University of Utah.
