Harmonization of Data from Two Complimentary U.S. Networks: CSN and IMPROVE Speciated Particulate Matter

As long-term speciated particulate matter monitoring networks, the Interagency Monitoring of Protected Visual Environments (IMPROVE) and Chemical Speciation Network (CSN) programs were designed with different objectives but employ similar methods and report similar species. Both networks provide nationwide coverage of speciated particulate matter on 24-hr averaged filter samples collected every three or six days. The IMPROVE program, managed by the National Park Service, was designed to monitor visibility in national parks, wilderness areas, and wildlife refuges, and most sites are in rural areas. The CSN is managed by the Environmental Protection Agency and has a public health focus with monitoring concentrated in urban areas. Combining data from the two networks for analysis of air quality trends provides excellent spatial coverage with over 300 sites and temporal coverage with data from IMPROVE and CSN back to 1988 and 2001, respectively. However, merging these data is challenging because of historical differences in data processing methodologies. Beginning in 2016, a renewed effort was made to harmonize data processing practices between the two networks, such as blank correction, uncertainty estimation, and detection limit calculation. These efforts have enabled better network intercomparisons, making the data more accessible to a wider audience. We present some of the key changes and select analyses using the CSN and IMPROVE combined data.