Total suspended particulate manganese in ambient air in Montreal 1981–2000

Our research group previously established the time variation of atmospheric Mn in Montreal for the period 1981–1992. The results indicated stable Mn concentrations between 1981 and 1990 followed by a decrease of almost 50% attributed to the closing of a ferromanganese plant located approximately 25 km from Montreal. The aim of this study is to assess the atmospheric concentrations of Mn in Montreal between 1993 and 2000, to compare these data to those for the period 1981–1992, and to evaluate the presence of any trend. Three sampling stations belonging to the Montreal Urban Community (MUC) air quality surveillance network were selected. Filters from 1993 to 2000 were obtained from the MUC archives. The first sample of each month was selected and chemical analysis was performed by neutron activation analysis. The mean annual atmospheric Mn concentrations in Montreal from 1993 to 2000 were found to be very stable. The mean Mn concentration calculated for this time period was 0.01 μg/m3 for station 99 (characterized by a low traffic density), which was significantly different (P<0.05) from the mean of 0.03 μg/m3 for stations 13 and 68 which had higher traffic densities. Even though Mn represented a small percentage of the TSP (varying between 0.02% and 0.14%), the comparison between Mn and TSP is interesting since the stable temporal profile of Mn since 1993 contrasts with the continuously decreasing atmospheric TSP concentrations. This observation suggests that the combustion of MMT used in gasoline could be contributing to maintaining stable atmospheric Mn levels.