Abstract
In this work, based on the existing studies on photochemical reactions in the lower atmosphere, an analysis of the historical series of NOx, NO2, and O3 concentrations measured in the period 2015–2019 by two monitoring stations located in the urban area of Turin, Italy, was elaborated. The objective was to investigate the concentration trends of the contaminants and evaluate possible simplified relationships based on the observed values. Concentration trends of these pollutants were compared in different time bands (diurnal or seasonal cycles), highlighting some differences in the dispersion of the validated data. Calculated [NO2]/[NOx] ratios were in agreement with the values observed in other urban areas worldwide. The influence of temperature on the [NO2]/[NOx] ratio was investigated. An increase of [NO2]/[NOx] concentration ratio was found with increasing temperature. Finally, a set of empirical relationships for the preliminary determination of NO2 concentration values as a function of the NOx was elaborated and compared with existing formulations. Polynomial functions were adapted to the average concentration values returned by the division into classes of 10 μg/m3 of NOx. The choice of an empirical function to estimate the trend of NO2 concentrations is potentially useful for the preliminary data analysis, especially in case of data scarcity. The scatter plots showed differences between the two monitoring stations, which may be attributable to a different urban context in which the stations are located. The dissonance between a purely residential context (Rubino station) and another characterised by the co-presence of residential buildings and industries of various kinds (Lingotto station) leads to the need to consider a greater contribution to the calculation of the concentrations emitted in an industrial/residential context due to a greater presence of industrial chimneys but also to more intense motorised vehicle transport. The analysis of the ratio between nitrogen oxides and tropospheric ozone confirmed that, as O3 concentration increases, there is a consequent reduction of NOx concentration, due to the chemical reactions of the photo-stationary cycle that takes place between the two species. This work highlighted that the use of an empirical formulation for the estimation of [NOx] to [NO2] conversion rate could in principle be adopted. However, the application of empirical models for the preliminary estimation of [NOx] conversion to [NO2] cannot replace advanced models and should be, in principle, restricted to a limited area and a limited range of NOx concentrations.
Highlights
The sudden changes in lifestyles, the continuous growth of the world population, the progress of technologies applied to combustion, industrial and agricultural processes, and the indiscriminate use of the territory cause a continuous evolution of the characteristics of atmospheric pollution, which need to be understood in order to intervene with effective measures
Nitrogen oxides (NOx) and ozone are among the most important pollutants contributing to the worsening of air quality in urban areas
For O3, international limits are between 0.05 ppm for the short-term exposure and 0.3 ppm for the long-term exposure (American Conference of Governmental Industrial Hygienists (ACGIH; U.S National Institute for Occupational Safety and Health (NIOSH))
Summary
The sudden changes in lifestyles, the continuous growth of the world population, the progress of technologies applied to combustion, industrial and agricultural processes, and the indiscriminate use of the territory cause a continuous evolution of the characteristics of atmospheric pollution, which need to be understood in order to intervene with effective measures. Thorough knowledge of the behaviour of certain chemical compounds generating atmospheric pollution represents the key point for air quality improvement. Such knowledge is the basis for the planning of specific. Nitrogen monoxide (NO) is a colourless gas; the limit value for the 8-h working exposure is 5 ppm. Nitrogen dioxide (NO2) is yellowish-brown in colour; the limit value for 8-h working exposure is 5 ppm. The health-based limit concentrations in the ambient air in Europe, as established by Directive 2008/50/ EU (European Union), are 40 μg/m3 for N O2 (yearly mean) and 120 μg/m3 for O3 (maximum daily 8-h mean). Reached the objectives for 2010 identified by the National Directive on Emission Limits, which defined the target value of 990 Gg (European Union 2001). Despite the positive trend, reducing the presence of NOx and O3 still represents a challenge for administrations (Magaril et al 2017)
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