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

摘要

A multiple linear regression model was used to investigate seasonal and long-term trends in concentrations of ozone (O_3) 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 O_3, sulfur dioxide (SO_2), nitric acid (HNO_3), and aerosol concentrations of sulfate (SO_4~(2-)), calcium (Ca~(2+)) and chloride (Cl~-). Of these, peak median concentrations occurred during the spring for O_3 and Ca~(2+), during the warmer, drier months (April-September) for SO_4~(2-) and HNO_3, and during the cooler, wetter months (October-March) for SO_2 and Cl~-. Statistically significant secondary cycles of 6 months duration were seen for concentrations of O_3, SO_4~(2-), HNO_3, Ca~(2+), and Cl~. Daily maximum O_3 concentrations exhibited a statistically significant increase over the period of record of 0.33 +- 0.26 ppb/yf. Statistically significant declines were found for concentrations of SO_2, SO_4~(2-), HNO_3, Ca~(2), and potassium, ranging from 20 to 36% from levels at the start of the sampling period. Declines in ambient concentrations of SO_2, SO_4~(2-), and HNO_3 reflect local declines in anthropogenic emissions of the primary precursors SO_2 and NO_x over the past decade. Trends in Ca~(2-+) and potassium ion concentrations are in line with a broader North American declining trend in acid-neutralizing cations.