Mobile sources often have the characteristic of high CONO ratios and low SO 2

Mobile sources often have the characteristic of high

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against emission inventories. Mobile sources often have the characteristic of high CO/NO ratios and low SO 2 /NO ratios, whereas higher SO 2 /NO ratios and lower CO/NO ratios are associated with point sources (energy production). Based on ambient data, Figure 3 provides the relationship between CO and NO, and RASHEED ET AL. © 2014 The Authors. 306
Earth’sFuture 10.1002/2013EF000174 Figure 2. Correlation between ambient concentrations of CO and PM 2.5 during 2007–2011. between CO and reactive nitrogen species, NO y , in Islamabad during 2007–2011. A linear regression of hourly average CO and NO, and CO and NO y was performed, which shows a significant ( p -value 0.01) correlation between CO and NO concentrations ([CO] = 10.13[NO] + 511.3; r 2 = 0.76) and a significant ( p -value 0.01) cor- relation between CO and NO y con- centrations ([CO] = 9.84[NO y ] + 256.8; r 2 = 0.78). From this ratio analysis, relative background concentrations may be determined by examin- ing the intercept of the regres- sion lines. The regression curves reveal a background CO con- centration of 300 to 600 ppbv in the Islamabad urban area. This is similar to Raleigh, NC, USA, urban site value of 470 ± 52 ppbv [ Aneja et al ., 1997]; however, CO background concentration in New Delhi, India, has been observed as approximately 1693 ppbv [ Aneja et al ., 2001]. Moreover, rel- ative source strengths like mobile sources versus point sources may also be suggested by exam- ining the slope of the regression lines, and compared with emissions inventory. Klimont et al . [2013] and ECCAD (Emissions of atmospheric Compounds & Compilation of Ancillary Data, 2014, , hereinafter referred to as ECCAD, online report, 2014) have provided an emissions inventory (developed for the year 2010) for CO, SO 2 , and NO x . Table 1 compares and contrasts the emissions from this inventory by examining the relationship between ambient CO and NO x , and between ambient SO 2 and NO x for 2007–2011 in Islamabad, Pakistan. It also compares and contrasts with CO and NO x relationship observed in Denver, CO, USA [ Parrish et al ., 1991]; Boulder, CO, USA [ Goldan et al ., 1995]; Raleigh, NC, USA [ Aneja et al ., 1997]; and New Delhi, India [ Aneja et al ., 2001]. Based on ratio analysis of CO and NO x , Parrish et al . [1991] reported values of 8.4, 7.8, and 10.2 for mobile sources in the Eastern United States, Pennsylvania area, and Western United States, respec- tively. Given the average ratio of about 10 (i.e., the slope of the regression line) in Islamabad, it appears that mobile sources contribute more to the concentrations of CO and NO x than point sources. Monthly averages of SO 2 concentration (1 μ g m 3 SO 2 = 0.38 ppbv) are plotted in Figure 4. Sulfur dioxide concentrations are below Pakistan’s 24 h average NEQS value of 120 μ g m 3 during the measurement (a) (b) Figure 3. Correlation between (a) CO and NO, and (b) CO and NO y during 2007–2011. RASHEED ET AL.

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