Open Air Chicago Hour Aggregations

Sensors deployed throughout the City by Open Air Chicago measuring fine particulate matter 2.5 (PM2.5) and nitrogen dioxide (NO2). All sensors collect data on PM2.5 and NO2. Six sensors also collect data on black carbon (BC) and current weather conditions.

1-hour mean measurements are calculated by averaging all individual measurements collected during a specific UTC hour. For instance, the 04:00 UTC 1-hour mean aggregates all measurements taken between 04:00:00 UTC and 04:59:59 UTC.

Additional aggregations, such as the NowCast and 24-hour rolling mean, use different time windows to calculate averages and are reported hourly. These aggregations provide specialized insights into air quality trends. NowCast aggregates measurements over a 12-hour window according to US EPA NowCast calculation rules, ending at the end of the reporting hour. For example, a PM2.5 NowCast concentration timestamped at 16:00 UTC includes data from 05:00 UTC to 16:59:59 UTC. 24-hour Rolling Mean averages measurements over a sliding 24-hour window, also ending at the reporting hour.

There are related datasets linked below that show the individual measurements and aggregations by day.

<b>Special Note: As of the launch date of this dataset, the black carbon modules are currently offline. All related metrics are unavailable until further notice and will appear as blank in the dataset.</b>

Some metrics have ready-to-use values directly from the sensor. No further processing occurs. Examples are temperature, relative humidity, and wind. Other metrics have raw data processed further in the Clarity cloud. We call these metrics "cloud-calibrated." Examples are PM2.5 and NO2, which have a global correction factor applied. Column names end in either .raw or .value. For direct-from-sensor metrics, raw and value are the same. For cloud-calibrated metrics raw is from the sensor and value is cloud-calibrated and different from raw.

For more information, please visit:  
www.clarity.io/blog/v2-1-pm2-5-global-calibration
www.clarity.io/blog/introducing-claritys-global-no2-calibration-model.

Metrics related to black carbon, ambient temperature, relative humidity, and wind speed and direction are for research purposes being conducted by UIC SPH. In addition to the 277 sensors deployed as part of the Open Air Chicago network, there are additional sensors installed at federal monitoring sites to inform the development of a potential local correction factor. 

This dataset is limited to measurements that have met Clarity's automated data quality control checks to ensure the data are high quality. For more information, please visit: https://click.clarity.io/knowledge/quality-control. If you are interested a dataset that includes invalidated data, please submit a data request at <a href="https://www.chicago.gov/city/en/depts/cdph/provdrs/health_data_and_reports/svcs/data-request-form.html" target="_blank">this link</a>.

Open Air Chicago is a citywide project consisting of 277 non-regulatory, air sensors installed in Summer 2025. It was founded by the Chicago Department of Public Health (CDPH) and the University of Illinois at Chicago School of Public Health (UIC SPH). The development of the network was supported by an advisory board and other partners, including the following: Alliance of the Southeast, Chicago Environmental Justice Network, Communities United, Grow Greater Englewood, Little Village Environmental Justice Organization, Neighbors for Environmental Justice, ONE Northside, Openlands. People for Community Recovery, Pilsen Environmental Rights and Reform Organization, Southeast Environmental Task Force, The Southwest Collective and the Westside Cultural Alliance, Chicago Department of Transportation, Cook County Department of Environment and Sustainability, Illinois Environmental Protection Agency, RHP Risk Management, University of Illinois Urbana-Champaign, Clarity Movement Company, and Illinois Public Health Institute.

Dr. Serap Erdal from UIC SPH was awa

Tags: air-quality, air-quality-index, aqi, health, nitrogen-dioxide, particulate-matter, public-health, sensors, weather
Organization: City of Chicago