Analysis of NO x , NO and NO 2 ambient levels in Dhahran, Saudi Arabia Khaled Gasmi ⁎, Abdulaziz Aljalal, Watheq Al-Basheer, Mumin Abdulahi Department of Physics, King Fahd University of Petroleum & Minerals, Dhahran 31261, Saudi Arabia article info abstract Article history: Received 24 June 2016 Received in revised form 28 May 2017 Accepted 2 July 2017 Available online xxxx NO x , NO, and NO 2 concentrations and meteorological parameters, tem- perature, wind speed, relative humidity and pressure were measured continuously in Dhahran from May to July 2015. Concentrations of NO x , NO, and NO 2 were found to be highly influenced by traffic emission and meteorological conditions. The temperature and wind speed showed negative correlation coefficients while relative humidity showed positive correlation coefficient with NO x , NO, and NO 2 concen- trations. NO 2 was found to exceed international air quality standards, which indicates the existence of possible NO 2 air pollution problem in Dhahran. © 2017 Elsevier B.V. All rights reserved. Keywords: NO x NO NO 2 Traffic emission Meteorological parameters 1. Introduction Nitrogen oxides (NO x = NO + NO 2 ) are considered one of the main pollutants in urban areas. They are very reactive and play a significant role in the chemistry of the atmosphere (Han et al., 2011; Richter et al., 2005; Wang and Mauzerall, 2006). Their concentrations in ambient air are the result of processes of accumu- lation, dispersion, transformation and removal (Mazzeo et al., 2005). In general, NO x concentrations vary rap- idly in urban areas over the course of the day with a typical residence time of about few days (Andrews et al., 2004). Although significant amount of NO x is produced naturally, for example, during lightning and from micro- bial activities in soils, the main source of NO x production in urban and industrial areas is from fossil fuel com- bustions, in particular, emissions from car engines (Agudelo–Castaneda et al., 2014; Carslaw, 2005; Itano et al., 2014; Kurtenbach et al., 2012; Zhao et al., 2015), which depend on vehicle type/size, fuel used and the manner of driving (Clapp and Jenkin, 2001). Urban Climate xxx (2017) xxx–xxx ⁎ Corresponding author. E-mail address: kgasmi@kfupm.edu.sa (K. Gasmi). UCLIM-00321; No of Pages 11 http://dx.doi.org/10.1016/j.uclim.2017.07.002 2212-0955 © 2017 Elsevier B.V. All rights reserved. Contents lists available at ScienceDirect Urban Climate journal homepage: http://www.elsevier.com/locate/uclim Please cite this article as: Gasmi, K., et al., Analysis of NO x , NO and NO 2 ambient levels in Dhahran, Saudi Arabia..., Urban Climate (2017), http://dx.doi.org/10.1016/j.uclim.2017.07.002