A report describing ambient levels of particulate matter (PM10 and PM2.5) within the province of British Columbia was prepared to aid in airshed planning and management. The 130-page report details temporal trends and patterns in PM concentrations at various sites throughout British Columbia up to the year 2000. PM concentrations are highest in the interior of the province and lowest in coastal communities. There are also large seasonal variations that vary from one region of the Province to another. Seasonal and spatial variations arise due to regional patterns in land use and industrial development, proximity of monitoring sites to PM sources, and regional differences in geography and meteorological conditions. The report is a technical document which will be of value to regulatory officers, air quality planners and scientists mainly within the federal, provincial and regional levels of government.
Key Points for Decision-Makers
Owing to large seasonal differences in PM concentrations that vary from one region of British Columbia to another, there is a need for each region to identify when it is most susceptible to higher concentrations and to develop PM management plans accordingly. These variations are particularly evident when comparing the highly urbanized Lower Fraser Valley with the interior of the province, and are a reflection of seasonal differences in source types and contributions and prevailing meteorology.
PM management plans may require the cooperation of multi-levels of government, given the range of sources that have been identified as major emitters of PM10 and PM2.5, and the number of jurisdictions having authority over these sources.
Separate approaches may be required to control PM10 and PM2.5, particularly where the focus is on reducing the more extreme concentrations.
In the Lower Fraser Valley , source apportionment studies and emission inventories suggest that PM management approaches should include the control of both direct PM emissions and PM precursor emissions.
In the interior, the significance of secondary PM has yet to be demonstrated; however, it would be prudent to begin identifying measures to reduce emissions of precursor gases such as NOx and SOx emissions which are overwhelmingly anthropogenic in nature.
In the interior, there is a need to apply source apportionment techniques based on the collection of speciated PM data, beginning in communities characterized by high PM concentrations and a number of different PM sources.
The long-range transport of pollutants has been shown to influence local PM levels, as demonstrated during Kosa Asian dust events. Furthermore, the Canada-Wide Standard (CWS) for PM and Ozone contains provisions for identifying communities where background, natural or transboundary sources contribute to exceedances of the CWS, and for Keeping Clean Areas Clean. To meet these provisions under the CWS, and ultimately to develop emission reduction initiatives that will be effective in reducing local PM problems, it will be necessary to obtain improved estimates of background PM levels and to better understand the mechanisms for long-range transport.
Meteorology plays a large role in the development of PM episodes. More needs to be known about the meteorological conditions and synoptic patterns most conducive to periods of poor air quality, as this will assist in our ability to predict such episodes.
To facilitate the tracking of long-term trends, it will be necessary to develop and maintain a stable network of PM2.5 stations that characterizes the major macroclimatic and ecologically distinct populated areas of the province.
Key Scientific Findings
PM concentrations are highest in the interior and lowest in the coastal communities.
Two predominant seasonal patterns of PM10 exist.
In the Lower Fraser Valley, the highest PM10 concentrations are observed during late summer while the lowest concentrations are found in late fall and winter.
At interior sites, the highest concentrations of PM10 are typically observed in late winter/early spring, and the lowest concentrations occur in early winter as well as in early summer.
Based on limited monitoring, the highest concentrations of PM2.5 occur during the fall. The Lower Fraser Valley also experiences higher PM2.5 concentrations during the later summer months, while the lowest concentrations typically occur during the winter.
PM10 concentrations are typically 30% higher at mid-week than on Sundays. There is also a diurnal pattern with peak concentrations occurring in mornings and evenings.
PM concentrations can vary considerably from one community to the next due to regional patterns in land use and industrial development, proximity of monitoring sites to PM sources, and regional differences in geography and meteorological conditions.
Occasionally, meteorological conditions persist that produce extended periods of high PM10 concentrations during which the provincial ambient air quality objective of 50 µg/m3 is exceeded. Episodes typically last between two and six days. In the interior, PM10 episodes are most likely to occur during February and March, although episodes have been reported in every month of the year. PM10 episodes occur very rarely in the Lower Fraser Valley and coastal regions of BC.
Based on the limited PM2.5 data available in the province, nine of 11 PM2.5 episodes up to 2000 have occurred in Prince George. PM2.5 episodes are most frequent between September and February, with none occurring during the month of March when PM10 episodes are most frequent in the province.
PM levels do appear to be decreasing at a number of sites in the province; however, they remain at levels that are associated with increased risks of potential health effects.
Limitations/Caveats/Uncertainties Associated with the Findings
A comprehensive evaluation of ambient levels of PM2.5 has been hampered by a lack of data. A much longer record exists for PM10 for which a provincial air quality objective exists. Our knowledge of porno gratis particulate matter in BC is based largely on PM10 monitoring augmented by limited measurements of PM2.5
Since concentrations of PM can vary widely over a small area, data from individual sites may not be representative of the air quality in the surrounding geographic area.
The relatively short monitoring history at most sites precludes a robust trend analysis of PM10 or PM2.5 data.