Assessing the intra-urban variability of nitrogen oxides and ozone across a highly heterogeneous urban area.

High-resolution air quality maps are critical towards assessing and understanding exposures to elevated air pollution in dense urban areas. However, these surfaces are rarely available in low- and middle-income countries that suffer from some of the highest air pollution levels worldwide. In this study, we make use of land use regressions (LURs) to generate annual and seasonal, high-resolution nitrogen dioxide (NO), nitrogen oxides (NO), and ozone (O) exposure surfaces for the Greater Beirut Area (GBA) in Lebanon. NO, NO and O concentrations were monitored using passive samplers that were deployed at 55 pre-defined monitoring locations. The average annual concentrations of NO, NO, and O across the GBA were 36.0, 89.7, and 26.9 ppb, respectively. Overall, the performance of the generated models was appropriate, with low biases, high model robustness, and acceptable R values that ranged between 0.66 and 0.73 for NO, 0.56 and 0.60 for NO, and 0.54 and 0.65 for O. Traffic-related emissions as well as the operation of a fossil-fuel power plant were found to be the main contributors to the measured NO and NO levels in the GBA, whereas they acted as sinks for O concentrations. No seasonally significant differences were found for the NO and NO pollution surfaces; as their seasonal and annual models were largely similar (Pearson's r > 0.85 for both pollutants). On the other hand, seasonal O pollution surfaces were significantly different. The model results showed that around 99% of the population of the GBA were exposed to NO levels that exceeded the World Health Organization defined annual standard.