Assessment of background particulate matter concentrations in small cities and rural locations—Prince George, Canada

Figures & data

Figure 1. Locations of the PM measurement stations analyzed in this study. Map (a) provides a rough overview of the overall study domain on the North American continent, map (b) illustrates the locations of all small cities in central British Columbia included in this study, and map (c) shows the specific location of the Plaza and Gladstone measurement stations in Prince George.

Figure 2. Low pollution sectors for the PG Plaza monitoring location identified by the geographical analysis. Light shading identifies forested areas. Hatching, cross hatching and stippling (with road network) indicate commercial, industrial, and residential areas, respectively. Major rivers are shown in white.

Figure 3. Analysis of low pollution sectors for Plaza. Rings indicate wind speed (m/s); shading is mean PM₁₀ concentration (µg/m³).

Figure 4. Low pollution sectors for the PG Gladstone monitoring location. For explanation of shadings, see Figure 2.

Figure 5. Analysis of low pollution sectors for Gladstone. Rings indicate wind speed (m/s); shading is mean PM₁₀ concentration (µg/m³).

Table 1. Annual and seasonal PM₁₀ and PM_2.5 background concentrations with 95% confidence intervals for the PG airshed based on Plaza 2000–2009 and Gladstone 2006–2009 data

Season	PM10 all data (µg/m^3)	PM10 dry (µg/m^3)	PM10 wet (µg/m^3)	PM2.5 all data (µg/m^3)	PM2.5 dry (µg/m^3)	PM2.5 wet (µg/m^3)	No. of obs.,all data
Annual	7.4 ± 0.2	9.7 ± 0.5	6.4 ± 0.3	2.2 ± 0.1	2.7 ± 0.2	2.2 ± 0.2	5012
Winter	5.8 ± 0.3	6.3 ± 0.7	5.4 ± 0.5	1.9 ± 0.1	1.9 ± 0.3	2.0 ± 0.2	1300
Spring	8.2 ± 0.4	10.2 ± 0.9	6.3 ± 0.6	2.2 ± 0.1	2.8 ± 0.3	1.7 ± 0.2	1828
Summer	7.5 ± 0.6	11.2 ± 1.7	6.2 ± 0.9	2.2 ± 0.4	3.5 ± 0.9	2.0 ± 0.6	975
Fall	7.9 ± 0.4	10.3 ± 1.1	7.5 ± 0.6	2.6 ± 0.2	2.7 ± 0.4	3.0 ± 0.4	1354
Note: The “No. of obs.” (Number of observations) column shows the number of hourly data points used for calculation of given means. See text for explanation of dry and wet conditions.

Figure 6. Seasonal variability of PM₁₀ background concentrations for the PG airshed based on both Plaza (2000–2009) and Gladstone (2006–2009) monitoring data. See text for explanation of dry and wet conditions. Error bars represent 95% confidence intervals.

Figure 7. Seasonal variability of PM_2.5 background concentrations for the PG airshed based on both Plaza (2000–2009) and Gladstone (2006–2009) monitoring data. See text for explanation of dry and wet conditions. Error bars represent 95% confidence intervals.

Figure 8. Seasonal PM_2.5 background percentiles for the PG airshed (50th, 75th, and 98th).

Table 2. Low pollution sectors and wind conditions for the six northern BC locations analyzed in this study

Location	Wind speeds	Low pollution sectors	Station coordinates	Data set range	Number of observations
PG Plaza	3–5 m/s	350–10˚ and 150–170˚ and 230–250˚	53.9147 N, –122.7425 W	2000–2009	2512
PG Gladstone	3–5 m/s	180–310˚	53.8592 N, –122.7633 W	2006–2009	2500
Quesnel West Correlieu School	3–6 m/s	90–310˚	52.9664 N, –122.5167 W	2000–2009	9013
Burns Lake Fire Centre*	2–4 m/s	180–360˚	54.2307 N, –125.7643 W	11/2006–12/2009	11,299
Houston Fire Hall*	2–4 m/s	0–360˚	54.3972 N, –126.6450 W	07/2001–12/2009	28,525
Smithers St Josephs	3–6 m/s	190–310˚	54.7830 N, –127.1775 W	07/2004–12/2009	2150
Note: *The geographic and pollutant-derived low pollution sectors did not agree for these stations; thus, the pollutant-derived low pollution sectors were applied. The method can be considered inappropriate for these stations.

Table 3. PM₁₀ background concentrations with 95% confidence intervals and related percentiles for all BC locations analyzed

Location	Mean PM10 (µg/m^3)	25th Percentile PM10 (µg/m^3)	50th Percentile PM10 (µg/m^3)	75th Percentile PM10 (µg/m^3)
PG Plaza	8.5 ± 0.3	4	7	11
PG Gladstone	6.3 ± 0.3	2	5	8
Quesnel	8.4 ± 0.2	4	6	10
Burns Lake*	(13.8 ± 0.3)	5	9.5	17
Houston*	(12.4 ± 0.1)	5	9	15
Smithers	7.2 ± 0.4	3	5	9
Note: *Values in parentheses indicate that the low pollution sector method fails.

Table 4. PM_2.5 background concentrations with 95% confidence intervals and related percentiles for all BC locations analyzed

Location	Mean PM2.5 (µg/m^3)	25th Percentile PM2.5 [(µg/m^3)	50th Percentile PM2.5 (µg/m^3)	75th Percentile PM2.5 (µg/m^3)
PG Plaza	2.5 ± 0.1	0	1	4
PG Gladstone	1.9 ± 0.1	0	1	2
Quesnel	2.5 ± 0.1	0	1	4
Burns Lake	2.2 ± 0.1	0	1	3
Houston*	(3.5 ± 0.1)	0	2	5
Smithers	1.8 ± 0.1	0	1	2
Note: *Values in parentheses indicate that the low pollution sector method fails.

Figure 9. PM₁₀ background PG airshed (mean of Plaza and Gladstone values) versus Smithers and Quesnel: 25th, 50th, and 75th percentiles of hourly means.

Figure 10. PM_2.5 background PG airshed (mean of Plaza and Gladstone values) versus Smithers and Quesnel: 50th and 75th percentiles of hourly means.

Figure 11. Annual PM (wet)/PM (dry) ratios for PM_2.5 (left) and PM₁₀ (right) for Prince George Plaza, Prince George Gladstone, Smithers, and Quesnel.

Table 5. Detailed sector analysis for annual PM background concentrations at PG Plaza

Sector(s)	Mean PM10 (µg/m^3)	Mean PM2.5 (µg/m^3)
350–10˚ and 150–170˚ and 230–250˚	8.4 ± 0.3	2.5 ± 0.1
0–10˚	10.3 ± 1.0	3.5 ± 0.5
150–160˚	8.9 ± 1.2	2.9 ± 0.5
160–170˚	8.8 ± 0.5	2.3 ± 0.3
230–240˚	7.7 ± 0.7	2.1 ± 0.3
240–250˚	7.8 ± 0.7	2.1 ± 0.3
350–360˚	8.3 ± 0.7	2.9 ± 0.3
Note: Uncertainties show 95% confidence intervals.

Table 6. Summary of background PM concentration values investigated by different authors

Author	Mean PM2.5(µg/m^3)	Mean PM10 (µg/m^3)	Area/location	Observation period
Trijonis et al., 1990	1.47	4.47	Western United States	1980s
U.S. EPA, 1996	1–4	4–8	Western United States	1990s
Cheng et al., 2000	3.2	8.8	Rural Alberta	2–24 months1993–1997
Putaud et al., 2004	3.5	5	Northern Finland	1991–2001
Vingarzan, 2007	1–3	6	Alberta/British Columbia	1999–2001

Figure 12. Comparison of annual and seasonal mean PM₁₀ background concentrations observed at Plaza 2000–2009 and Gladstone 2006–2009. Error bars show 95% confidence intervals.

Figure 13. Comparison of annual and seasonal mean PM_2.5 background concentrations observed at Plaza 2000–2009 and Gladstone 2006–2009. Error bars show 95% confidence intervals.

Figure 14. Comparison of the PG airshed annual PM₁₀ and PM_2.5 concentrations (blank stars) to Smithers and Quesnel (shaded stars) as well as literature values. Diamonds indicate mean annual background values; triangles indicate minimum and maximum background levels investigated by former authors; see also Table 6.

Trijonis , J.C. , Malm , W.C. , Pitchford , M. , Charlson , R. and Husar , R. 1990 . Natural Background Conditions for Visibility/Aerosols. NAPAP Report 24, section 3.5 , Washington , DC : National Acid Precipitation Program .

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