Temporal Variation in Daily Concentrations of Ozone and Acid-Related Substances at Saturna Island, British Columbia

Abstract

A multiple linear regression model was used to investigate seasonal and long-term trends in concentrations of ozone (O3) and acid-related substances at the Saturna Island monitoring station in southwestern British Columbia from 1991 to 2000. Statistically significant primary (dominant) cycles with a period of 1 yr were found for O3, sulfur dioxide (SO2), nitric acid (HNO3), and aerosol concentrations of sulfate (SO4 2−), calcium (Ca2+) and chloride (Cl−). Of these, peak median concentrations occurred during the spring for O3 and Ca2+, during the warmer, drier months (April-September) for SO4 2− and HNO3, and during the cooler, wetter months (October-March) for SO2 and Cl−. Statistically significant secondary cycles of 6 months duration were seen for concentrations of O3, SO4 2−, HNO3, Ca2+, and Cl−. Daily maximum O3 concentrations exhibited a statistically significant increase over the period of record of 0.33 ± 0.26 ppb/yr. Statistically significant declines were found for concentrations of SO2, SO4 2−, HNO3, Ca2+, and potassium, ranging from 20 to 36% from levels at the start of the sampling period. Declines in ambient concentrations of SO2, SO4 2−, and HNO3 reflect local declines in anthropogenic emissions of the primary precursors SO2 and NOx over the past decade. Trends in Ca2+ and potassium ion concentrations are in line with a broader North American declining trend in acid-neutralizing cations.