CityAQ: Reliable Localized Air Quality Forecasts for More Cities
Despite the multiple reasons to reduce air pollution around the world, many cities, particularly in low- and middle-income countries, lack the data management tools as well as financial and human resources to improve their air quality. If cities could gain access to high-resolution visualized forecasts, city governments would be able to design better interventions and control policies, civil society could monitor compliance with city policies and residents can act based on real-time information.
City AQ: A localized solution
The CityAQ project was conceived to provide reliable, locally relevant, accessible air quality forecasts data and visualizations to resource-constrained cities facing air quality challenges, by leveraging the data available from local monitoring networks and global forecasts. CityAQ utilizes the tools and expertise of the National Aeronautics and Space Administration’s (NASA) in collaboration with local experts in participating cities, WRI and other organizations such as OpenAQ.
WRI, NASA, and cities collaborated to develop CityAQ, combining global models with data from local air quality monitoring networks to produce optimized forecasts with spatial and temporal resolutions useful for local decision making.
In a pilot phase, WRI identified a set of cities in Latin America, Africa and Asia that could benefit from these air quality forecasts. The selection required cities to have continuous and systematic monitoring using regulatory-grade instruments for ozone (O3), nitrogen dioxide (NO2) and particulate matter less than 2.5 micrometers (PM2.5), as well as hourly observations valid from 2018 onwards. The final set included the following cities:
- Jakarta, Indonesia
- Addis Ababa, Ethiopia
- Guadalajara (Metropolitan Area), Mexico
- Monterrey (Metropolitan Area), Mexico
- Guanajuato State, Mexico
- Bogota, Colombia
- Sao Paolo, Brazil
WRI’s Air Quality team has worked with air quality experts in these cities, preparing and sharing data from their local monitoring stations, which would then be used to generate the adjusted CityAQ forecasts. In the process, WRI helped facilitate greater access to available global air quality information by including the local air quality data in the air quality platform OpenAQ and WRI’s Resource Watch platform.
Tracking Air Pollutants
Transport and other urban activities emit large amounts of pollutants into the atmosphere which, depending on meteorological conditions, can remain over the city for some time or be quickly transported to other regions. In the atmosphere, pollutants are gradually transformed into species of greater toxicity than those that gave rise to them. The 3 main pollutants that are the subject of CityAQ’s forecasts are:
- Nitrogen dioxide (NO₂)(¹): one of a group of highly reactive gases known as nitrogen oxides (NOx). NO is used as the indicator for the larger group of nitrogen oxides. NO₂ primarily gets in the air from the burning of fuel.
- Tropospheric ozone (O₃)(²): Ozone at ground level is a harmful air pollutant because of its effects on people and the environment, and it is the main ingredient in “smog”. It is a secondary gas formed by the interaction of sunlight with hydrocarbons and nitrogen oxides, which are emitted by vehicles, fossil fuel power plants, and other manmade sources.
- Particulate matter (PM₂.₅)(³): refers to solid and liquid particles that are suspended in the air. These are predominantly the result of fossil fuel combustion. PM2.5 refers to particles with diameter less than 2.5 μm—3% the diameter of a human hair.
As of June 2021, the daily updated forecasts generated by CityAQ for O3, NO2 and PM2.5 are publicly available and visualized on Resource Watch’s open data platform. This platform also offers tools that allow users to access other social and environmental datasets from the vast catalog to generate valuable insight into air quality issues in a quick and intuitive way. Forecast visualizations on Resource Watch can be easily embedded into other websites, such as official web pages of participating cities.
How CityAQ Works
Some cities also employ models for air quality forecasting and diagnostic purposes. Air quality forecasts are very valuable as they allow governments and the public to take informed action. With adequate communication of the data and visualizations from these forecasts, people are able to protect themselves from risk, especially those who are more susceptible to variation in air quality, such as those with respiratory or cardiovascular conditions, young children, and pregnant women. Mexico City is a good example of this: The local government has developed their own forecast, combining a weather model, an emissions model, and a chemical transport model.
Forecasts allow decision-makers to proactively plan to mitigate the effects of a pollution event in different ways: warning the population, alerting their health systems, canceling outdoor events or reducing emissions that would exacerbate conditions. They also allow them to estimate the behavior of pollutants during an event originating outside their jurisdiction. The forecast is a key element that allows authorities to design and enforce control strategies to achieve systemic reductions in air pollution.
While not all cities currently have forecast models developed specifically for their city, global air quality tools, such as the Goddard Earth Observing System Composition Forecast (GEOS-CF) allow for the unprecedented opportunity to access continuously updated air quality forecasts anywhere in the world. However, these global models have a coarse spatial resolution for city management purposes (e.g., GEOS resolution is 25 x 25 km2), which makes it difficult to identify local phenomena that will affect air quality in the city.
Figure 2. Forecast of fine particulate matter (PM2.5) at monitoring station level for the next five days. Source: OpenAQ (GMAO-NASA/WRI)
Full dataset: https://bit.ly/3AvnnY2
CityAQ works by adjusting the outputs of the global GEOS-CF model developed by NASA, taking into account data from the monitoring sites of participating cities. This is done through the use of a machine learning algorithm, trained to fit the global model predictions to the geographic location of the observation site.
CityAQ In Action
Throughout the pilot phase, the need and importance of producing quality data has been emphasized, not only for regulatory purposes but also for other purposes such as modeling, visualization and evaluation of emerging technologies (e.g., satellite data, low-cost sensors). The interest by all the participant cities’ environmental authorities was remarkable, driven by the need for a forecasting system for their cities and the opportunity to collaborate on this project with WRI and NASA.
Forecasted Average NO₂ concentrations for Sao Paulo’s monitoring stations.
Source: CityAQ (GMAO-NASA/WRI)
Full dataset: https://bit.ly/3CBdmdK
Forecasted Average O₃ concentrations for Sao Paulo’s monitoring stations. Source: CityAQ (GMAO-NASA/WRI)
Full dataset: https://bit.ly/3lVvVmP
Currently, the participating cities are exploring potential applications for the forecast. For example, the Secretary of Sustainable Development of Nuevo León disseminates the air quality forecast for the Metropolitan Area of Monterrey (Mexico) through its website and mobile application, allowing citizens to anticipate risks in the event of a possible pollution episode. In Bogota, Colombia, the District Environment Secretary, which has an air quality forecast system, also uses the GEOS-CF adjusted forecast as a tool. In Leon, Guanajuato, the air quality forecast will be included on its website to inform the population.
In the near future, the partners will seek to expand the project, increasing the number of cities that have access to an air quality forecast. WRI also continues to collaborate in the improvement of data collection and monitoring capabilities, in addition to supporting the implementation of the forecast for the cities participating in the pilot stage.
Watch the featured webinar, with government representatives from participating cities sharing their experience around the project
For more information about CityAQ: https://www.wri.org/initiatives/cityaq
Armando Retama is a specialist in air quality issues and collaborates as a consultant with WRI Mexico.
Beatriz Cárdenas is director of air quality for WRI Mexico and a global air quality co-leader.
Sergio Baldit is Communications Specialist at Resource Watch.
Eduardo Castillero is Analyst at Resource Watch.
Beth Elliott is the Communications and Engagement Lead for Air Quality, WRI Ross Center for Sustainable Cities
