Click here to read the full report or an excerpt below.
NAPS data for metals in PM10 were analysed for Castlegar and Trail – Butler Park. The Trail data had a 14-month gap in it from late 1995 through late 1996 while the station was shut down during construction of a community recreation centre at Butler Park. During the seven year scope of this report declining trends in arsenic, cadmium and lead were found; there was no change in zinc levels.
Arsenic levels at Castlegar and Trail have been quite low since 1995, with very few exceedences of the BC 24 hour Level A objective except for a period between August and October 1999 when elevated levels were observed at Trail. The annual median values at these two sites are close to the detection levels, and annual maximum values have dropped steadily from 1993 to 1999.
Cadmium also has declined, with few values above the detection limit at either site since 1997. The annual median values at Trail and Castlegar have been equal to the detection limits at each site, and maximum annual values have declined towards the detection limit as well.
Lead levels, which have historically been of concern at Trail, have declined sharply since 1995, with the last exceedence of BC 24 hour Level A objectives occurring in 1997. Annual maximum values observed each year have declined to the detection limit at Castlegar, and are below the Level A objective at Trail.
Zinc in airborne particulate matter at Trail was lower in 1997 – 1999 than the high values observed in 1994 – 1995, but the 7 year time series shows no clear trend. Values of PM zinc at Trail in 1999 included many exceedences of the BC 24 hour Level A objective, and 2 exceedences of the Level B objective. Castlegar zinc levels were higher in 1999 than previously, with a higher median value and more exceedences of Level A and Level B objectives than in earlier years.
Sulphur Dioxide (SO2)
Sulphur dioxide was monitored hourly at Robson and Trail – Butler Park from 1993 through 1999 with one major gap in monitoring at Trail from November 1995 till June 1996 (as noted above). Clear declining trends are shown in ambient SO2 at both sites; there have been no exceedences of the 24-hour Level A objective since 1996 in either community.
Ambient SO2 at Robson has fallen steadily from 1993 in which there were 6 exceedences of the 1-hour Level A objective and 9 exceedences of the 3-hour Level A objective (no exceedences of the Level B objective at Robson) to no exceedences of any kind in 1997 through 1999. The plot of the daily cycle of ambient SO2 shows a well-defined peak in mid-morning; this is a meteorological phenomenon in which a ‘calm’ (i.e. poorly ventilated) period sets up each day and the airshed can accumulate suspended pollutants for a number of hours.
Trail – Butler Park sulphur dioxide concentrations have been higher than at Robson but have also fallen, especially since 1996. Exceedences of the 3-hour objectives were more common than 1- hour or 24-hour exceedences, emphasising the characteristic brief pulses of high SO2 that occur in this dataset. Exceedences of all Level B objectives (1-hour, 3-hour and 24-hour) have decreased since 1995, and there were no Level B exceedences observed in 1999. Level A exceedences (all durations) have also become infrequent with only 12 exceedences of the 1-hour objective, 8 exceedences of the 3-hour objective and 1 exceedence of the 24-hour objective in 1999. The daily cycle of SO2 at Trail shows two well defined peaks; the major one occurs in late morning and a smaller one in the late evening.