Introduction to Air Pollution

Challenges in Air Pollution

In this module, I'll be describing some challenges related to air pollution. But before I do that, think about the last time you checked your phone or a website for the weather. You probably checked for the weather forecasts to see what you should wear that day, but did you notice that virtually every app and website out there also has an air quality index or AQI listed there. If you did notice this, you may also have realized that AQI number can change pretty dramatically over a relatively short period of time and also over a relatively short distance. So the ability of air pollution to change rapidly over time and space is one of the main challenges, but not the only challenge we face in trying to understand the environmental health impacts of air pollutants. If we review some of the primary global air pollution problems, there's really five that come to mind. The first is stratospheric ozone depletion, causing additional ultraviolet radiation exposure to people at ground level. The second is atmospheric deposition of things like mercury and persistent organic pollutants, this meaning that those pollutants can get into the air, move around the atmosphere, and then deposit far away from where they were originally created. Urban smog is the third with a primary focus on particulate matter and ozone. Climate change is an enormous fourth one here driven primarily by greenhouse gas emissions, and a fifth one is indoor air pollution in households. So if we look at this list, you probably notice that three of these are a direct result of fossil fuel emissions. Now despite the fact that we know fossil fuel emissions are driving some of our worst air pollution problems, the use of some categories of fossil fuels has continued to grow. On this graph we're looking at energy consumption by source for the entire world. So on the y-axis here, you'll see the amount of energy being consumed, on the x-axis, we're going from 1990 to 2015, these are data which we have available and from 2015 to 2040 these are projections, and then the lines you see on this graph correspond to different types of energy sources. So there's some good news on this graph, the green line, renewables is increasing over time, and the dark line, coal has actually stabilized, in fact started to reduce slightly over time. So that means more clean energy coming online and less use of coal. That's the good news. The bad news is that natural gas and petroleum and other liquids are projected to continue to increase over time and Nuclear Energy at the very bottom of the graph which is clean and doesn't produce any fossil fuels is relatively stable historically and is not projected to grow. So beyond energy sources, which are very strongly linked to challenges and exposure assessment, we have other challenges as well. One of them is low exposure levels. While there are certainly areas around the world that it can have quite high air pollution, most of us have relatively low levels. Higher levels are easier to connect to exposure impacts because the health effects tend to be more obvious, Bub these chronic low level exposures can be quite challenging to understand. A second challenge is a mixture of chemicals. Air pollution is not a single chemical, it's thousands of chemicals and trying to understand the individual impacts of each is very very difficult. Third, we have extremely large variability in air pollutants over time and over space. Fourth, we have multiple exposure routes. So some types of pollution that we might breathe in like lead, could also come into us in other ways. So for example we may inhale lead, but we might also be eating lead on food that's been contaminated or drinking lead in water. So these multiple exposure routes for a particular pollutant make this job even more challenging. Finally, we have very long-term exposures. It can be relatively simple to understand a single air pollutant that you're exposed to over a single short amount of time, but as we start to think about years or decades or even a lifetime exposure, the uncertainties grow quite large. We also have challenges in assessing the impacts of the many policies we put into place to try to protect our health from air pollutants. So one is that changes in air pollution levels occur slowly over time. A second is that the sources of air pollution change over time due to different economic factors. A third again, is that health effects might be caused by multiple exposures not just air pollution. So again with that example of lead is that the lead your breathing in or the lead your drinking or the lead contaminating your food that's causing the health outcome. Of course it's all three in combination but one of them might be primary, and we tried to understand that. Finally, I want to highlight the complexity of the standard setting and policy making process, and I'm going to do this by highlighting the process for revising the National Ambient Air Quality Standards or NAAQS. So here we're looking at a very complex graph that we'll walk through in detail, and again this is an overview of the process the Environmental Protection Agency goes through to review the NAAQS for potential update. So we'll focus on the blue boxes in the center of the graph to begin with, the starting step here is an Integrated Review plan. This is basically setting forth the timeline and also trying to identify what are the key policy relevant in scientific questions. The next step down blue box is an integrated science assessments. So this is an evaluation and a synthesis of the policy relevant studies that are available. The third step is a risk and exposure assessments. We want to quantify how much and how often are people exposed to these NAAQS criteria air pollutants, focusing on key results and also identify uncertainties, what don't we know, and then the fourth layer of blue boxes is a policy assessment. So this is a staff analysis by EPA staffers on the different policy options that might be available to potentially consider. I want to highlight there's inputs on all of these blue boxes from various agencies including in yellow, the Clean Air Scientific Advisory Committee of the EPA. So they're going to be reviewing each of these steps and you'll notice there's also a box for public comment. We want the public to be able to provide input as well. When we transitioned from the blue part of the graphic to the green part, here you can see we start to enter agency decision-making so the staff are preparing to make changes that might be necessary, the staff at the EPA are also going to have review by other agencies. So this is a so-called inter-agency review. Then the EPA is going to propose discussions on the standards that they think should be put into place. We'll have another set of public hearings and input there. Then the agency will actually make its decision synthesizing all of this input they've gotten along the way, there will be another inter-agency review. So other professionals in the federal government putting their eyes on the policy, and then finally the decision is made and whatever changes are implemented. So you can see this is a quite complex process with many many steps and many parties involved. So policy making is challenging and it can certainly take a very long time, but I don't want to leave you with the impression that it's not effective. So here are two examples of where policies have been extremely effective. These policies specifically focusing on reducing lead exposure in the public. In the left-hand graphic we're looking at the United States and we can see here two types of lead that are represented in green, we have the lead that is allowed to be used in gasoline between 1975 and 1980, and in red we have the average blood lead levels of Americans sampled for this purpose. So you can see in 1975, the EPA basically started to phase out lead in gasoline, in 1977, the Consumer Product Safety Commission or CPSC banned lead-based paint, and you can see with these two actions the decline in the green line, lead used in gasoline became pretty precipitous after about 1978 and the average blood lead levels in America declined at basically the same rate. So we elected to eliminate lead in two important sources, and in this case, one of them leaded gasoline seems to have made a huge difference in terms of improving public health by reducing blood lead levels. In the right, we see a graphic from South Korea, and again here we have represented in the blue and red circles, blood lead levels measured in adults and children over time, and in green we have the ambient air lead levels. So South Korea was later to adopt a leaded gasoline ban. Theirs didn't really come into effect until the late 80's and early 1990's, but you can see the green line starts to drop precipitously once leaded gas is eliminated and you can see the blood lead levels declined along with that. While policy making is challenging and exposure assessment is challenging as well, both of these steps are key for us to do a better job at promoting environmental health.