Spatial and temporal analysis of ground level ozone and nitrogen dioxide concentration across the twin cities of Pakistan

Abstract

The analyses presented in this paper include the concentration levels of NO2 and O3 measured during 2 successive years in twin cities (Rawalpindi and Islamabad) of Pakistan from November 2009 to March 2011. NO2 was determined using the passive sampling method, while ozone was determined by Model 400E ozone analyzer. The average NO2 and O3 concentration in twin cities of Pakistan was found to be 44 ± 6 and 18.2 ± 1.24 ppb, respectively. Results indicate that the concentration of NO2 and O3 show seasonal variations. Results also depict that NO2 and O3 concentration levels are high in areas of intense traffic flow and congestion. Rawalpindi has more elevated levels of NO2 and O3 as compared to the Islamabad due to the narrow roads, enclosing architecture of road network and congestion. Climatic variables also influenced the NO2 and O3 concentration, i.e., temperature is positively related with O3, while negatively related with NO2, relative humidity is directly related with NO2 and inversely related with O3, whereas rainfall show negative association with both NO2 and O3 concentration. Comparing the results with WHO standards reveals that NO2 concentration levels at all the sampling points are above the permissible limit, while ozone concentration is still lower than the WHO standards. Thus, there is a need to take appropriate steps to control these continuously increasing levels of NO2 and O3 before they become a serious hazard for the environment and people living in those areas.

An evaluation of CMAQ NO2 using observed chemistry‐meteorology correlations

“…Correlations between NO 2 and meteorological variables have been investigated quantitatively at individual ground‐based locations [ Delaney and Dowding , ; Noble et al ., ; Roberts‐Semple et al ., ; Song et al ., ], at multiple ground‐based sites within urban areas [ Ahmad et al ., ; Ahmad and Aziz , ; Hatzianastassiou et al ., ], and qualitatively described as part of discussion of seasonal trends [e.g., Prasad et al ., ; Wei et al ., ]. These relationships are summarized in Figure and discussed below for each meteorological variable examined.…”

“…When OH is converted to the peroxy radical (HO 2 ) in the presence of ozone or VOCs, production of NO 2 from NO can be enhanced, but OH can also negatively impact NO 2 concentrations via reactions that form nitric acid [ Jacob , ]. A number of studies have found NO 2 concentrations positively correlated with RH [e.g., Ahmad et al ., ; Ahmad and Aziz , ; Noble et al ., ; Reddy et al ., ; Roberts‐Semple et al ., ; Song et al ., ]. Correlations between NO 2 and RH can be complicated by precipitation and by temperature.…”

“…Relative humidity is often higher when temperatures are low [e.g., Ahmad et al ., ; Noble et al ., ], so the multiple ways in which temperature affects NO 2 (discussed below) complicate the relationship with RH. Though NO 2 may be correlated with either absolute or relative humidity, throughout this analysis we focus on NO 2 correlations with relative humidity since it is less reflective of temperature and consistent with previous studies [ Ahmad et al ., ; Ahmad and Aziz , ; Noble et al ., ; Reddy et al ., ; Roberts‐Semple et al ., ; Song et al ., ].…”

Examination of the Relationship between Urban Air Pollution and Urban Planning Decisions in Cigli Case, Izmir (Turkey)

“…Due to the increase of motor vehicles in traffic in the study area, dense population and building blocks located in the center and southern parts of the study area, meteorological and topographical factors (Briggs et al, 2008, Mayer, 1999, Ahmad and Aziz, 2013, Lee et al, 2013, Lin et al, 2013, Zbieranowski and Aherne, 2012, Evci, 2009, Yang et al, 2005, the level of nitrogen dioxide (NO2) concentrations are higher in these points. …”

“…Briggs et al (2008), Mayer (1999), Ahmad and Aziz (2013) focus on nitrogen dioxide (NO2) that is a secondary pollutant and derived from especially motor vehicles. Brauer et al (2003) and Nerriere et al (2005) focus on particulate matter (PM10 and PM2.5) as an urban air pollutant causes a decrease in the level of air quality, while the level of individual exposure to pollution increases in urban areas.…”