Evaluation of two collocated federal equivalent method PM(2.5) instruments over a wide range of concentrations in Sarajevo, Bosnia and Herzegovina

Two widely used PM(2.5) monitors in the United States (U.S.) designated as federal equivalent methods (FEMs) by the U.S. Environmental Protection Agency were collocated for 15 months in Sarajevo, Bosnia and Herzegovina (BiH) to evaluate their comparability. With differing measurement principles, the FEMs (Met One BAM-1020 and Teledyne API T640) exhibited unique responses to the significant range in PM(2.5) over the study period. During the winter months when concentrations greatly increased (e.g., daily PM(2.5) > 100 μg m(−3)), the BAM-1020 had intermittent malfunctioning nozzle contact to the collection tape, resulting in periods of data invalidation. Increased operator observation and doubling the cleaning frequency were required to maintain proper operation. The hourly data from the BAM-1020, which detects PM(2.5) via beta-attenuation of particles loaded to the collection tape, indicated higher noise at concentrations below 40 μg m(−3) relative to the T640, which detects PM(2.5) via an optical method. Above this concentration threshold, the two instruments appear to have comparable hourly fluctuations in the data. Relative to the BAM-1020, the T640 reported higher concentrations when PM(2.5) is above 80 μg m(−3). A linear regression equation was developed and applied to adjust T640 PM(2.5) high concentration values, resulting in 24-hr average T640adj PM(2.5) values closely matching that from the BAM-1020 for the full concentration range. Based on the T640adj values, the annual average for Sarajevo was calculated at the site to be 42 μg m(−3), with significant seasonality resulting in over 7-fold higher concentrations in the months of December–January compared to June–July.