The Fourth Wave
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The Fourth Wave

Small sensors, hyperlocal data, and a high-tech look into Houston’s air pollution

By Ramon Alvarez, Environmental Defense Fund

Houston, Texas

Rapid innovation is making air pollution sensing technology a key tool in environmental protection. EDF’s recent work in Houston demonstrates how it allows us to not only see block-by-block pollution levels, but also how those levels compare to the rest of the city. We know that pollution doesn’t distribute evenly. This study, published in Environmental Science + Technology, shows us that in some cases, local road pollution was as much as 9 times higher than the average across all areas we measured.

Despite dramatic improvements in air quality in American cities over the last few decades, many communities still struggle with impacts from local air pollution. In Houston, many of the neighborhoods we studied lack air pollution monitors, and some important aspects of fine particulate matter — which research shows is an important contributor to many health effects from air pollution exposure — are not routinely measured at all in the region.

Together with our partners at Rice University and Google Earth Outreach, our team deployed mobile air quality sensors across Houston that allowed us to see, for the first time, where key pollutants exceeded typical pollution levels.

Seeing where air pollution is at its worst

Over the course of 9 months, two Google Street View cars carried fast-response air pollution sensors that measured black carbon, nitrogen oxides and fine particle levels every 1 to 5 seconds, providing pollution estimates on 50-meter long road segments. The cars drove a total of 52,000 kilometers of Houston streets, covering 35 Houston neighborhoods and comprising an 85 square kilometer area — the largest mobile monitoring dataset of its kind to date. Every road segment was measured at least 15 times. Some were measured as many as 44 times.

This approach produced about 30 million time-stamped data points that we turned into precise air pollution maps that show both where and at what levels elevated pollution was detected. Our measurements also probed how daytime pollution levels varied under different weather conditions. And for the first time, we were able to see how individual roads compared to the entire area we measured. For example, we could see that on-road pollution on certain arterial and local roads was 2 to 9 times higher than average levels across all measured neighborhoods.

Surprisingly, areas around industrial sites like concrete batch plants and metal recyclers produced readings that match air pollution around freeways. In some cities, these kinds of pollution sources are located in specific areas of town, away from sensitive groups. In Houston, however, many of these polluters are inside or next to residential neighborhoods, including places where children walk to school. Understanding where the worst pollution is and who it impacts can help lead to more meaningful mitigation.

Using new technology to tailor solutions

In the future, researchers could use our approach to identify areas with the highest polluting vehicles, to monitor in near-real time when and where pollution levels downwind of industrial facilities spike above typical levels, to fingerprint the source of pollution plumes, and to assess the impacts of the pollution patterns on public health.

For scientists, this kind of research opens up new approaches for analysis. For local officials, regulators and community groups, however, the impact could be even more profound. Air pollution is complicated, and traditional solutions to combat it have been based on continuous measurements at a few sparse sites across a broad region or regional data from satellites that measure once per day. With this new approach, people can see — street by street– where their city’s worst hotspots are and tailor solutions that make the biggest impact.

We are entering a new era of environmental innovation that is driving better alignment between technology and environmental goals — and results. #FourthWave



Environmental progress doesn't just happen. It's been propelled by successive waves of innovation, each unleashing powerful new tools: Land conservation. Force of Law. Power of Market-Based Solutions. Today we are seeing the emergence of a Fourth Wave of environmental innovation.

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Environmental Defense Fund

We work with businesses, governments and communities to create lasting solutions to the most serious environmental problems. We’re EDF.