Comparison of recent speciated PM2.5 data from collocated CSN and IMPROVE measurements

As long-term speciated PM2.5 monitoring programs, the Interagency Monitoring of Protected Visual Environments (IMPROVE) and Chemical Speciation Network (CSN) were designed with different objectives but apply similar analytical methods to 24hr filter samples and report many of the same species. The two networks have different operating structures, sampling practices, analytical methods, analytical facilities, and data handling and validation practices, which require attention when data from the two networks are combined in an analysis. Data from collocated CSN and IMPROVE sites from January 1, 2016 through September 30, 2018 are presented to document the comparability between the networks. While species measured well above the method detection limit (MDL) generally agree well during this period, there is evidence of some inter-network bias for fine-soil related elements at specific locations, as well as subtle biases for some well-measured species. Many species - particularly for CSN - are measured at or near the MDL and have poor inter- and intra-network collocated agreement; caution should be used when advancing findings on such measurements. However, comparison of reconstructed mass shows good inter-network agreement suggesting that the networks are effective at quantifying predominant mass species.