Role of Meteorological Parameters in the Diurnal and Seasonal Variation of NO in a Romanian Urban Environment.

The main purpose of this study was to investigate whether meteorological parameters (temperature, relative humidity, direct radiation) play an important role in modifying the NO concentration in an urban environment. The diurnal and seasonal variation recorded at a NO traffic station was analyzed, based on data collected in situ in a Romanian city, Braila (45.26° N, 27.95° E), during 2009-2014. The NO atmospheric content close to the ground had, in general, a summer minimum and a late autumn/winter maximum for most years. Two diurnal peaks were observed, regardless of the season, which were more evident during cold months. Traffic is an important contributor to the NO atmospheric pollution during daytime hours. The variability of in situ measurements of NO concentration compared relatively well with space-based observations of the NO vertical column by the Ozone Monitoring Instrument (OMI) satellite for most of the period under scrutiny. Data for daytime and nighttime (when the traffic is reduced) were analyzed separately, in the attempt to isolate meteorological effects. Meteorological parameters are not fully independent and we used partial correlation analysis to check whether the relationships with one parameter may be induced by another. The correlation between NO and temperature was not coherent. Relative humidity and solar radiation seemed to play a role in shaping the NO concentration, regardless of the time of day, and these relationships were only partially interconnected.