View article

PM_2.5 nitrate and sulfate () were measured continuously with R&P8400N and R&P8400S instruments, respectively, and compared with filter-based measurements at the Fresno Supersite from October, 2000 through December, 2005. concentrations were higher in winter than summer with a long-term decreasing trend. Correlations between 24-h average continuous and filter-based were greater than 0.96 in 4 out of 5 years. Continuous was generally lower than filter-based although the difference decreased over time, from −52% in 2001 to +13% in 2005. These differences were similar in winter (−23%) and summer (−19%) while the corresponding differences between ambient and instrument temperature were −12 and 0.7°C, respectively. Neither seasonal nor long-term trends in can be explained by variations in ambient temperature, the difference between ambient and instrument …