Analysis of the air pollution climate at a background site in the Po valley

Abstract

The Po valley in northern Italy is renowned for its high air pollutant concentrations. Measurements of air pollutants from a background site in Modena, a town of 200 thousand inhabitants within the Po valley, are analysed. These comprise hourly data for CO, NO, NO(2), NO(x), and O(3), and daily gravimetric equivalent data for PM(10) from 1998-2010. The data are analysed in terms of long-term trends, annual, weekly and diurnal cycles, and auto-correlation and cross-correlation functions. CO, NO and NO(2) exhibit a strongly traffic-related pattern, with daily peaks at morning and evening rush hour and lower concentrations over the weekend. Ozone shows an annual cycle with a peak in July due to local production; notwithstanding the diurnal cycle dominated by titration by nitrogen oxide, the decreasing long term trend in NO concentration did not affect the long term trend in O(3), whose mean concentration remained steady over the sampling period. PM(10) shows a strong seasonality with higher concentration in winter and lower concentration in summer and spring. Both PM(10) and ozone show a marked weekly cycle in summer and winter respectively. Regressions of PM(10) upon NO(x) show a consistently greater intercept in winter, representing higher secondary PM(10) in the cooler months of the year. There is a seasonal pattern in primary PM(10) to NO(x) ratios, with lower values in winter and higher values in summer, but the reasons are unclear.

Observational assessment of the role of nocturnal residual-layer chemistry in determining daytime surface particulate nitrate concentrations

“…It may be that production of NO − 3 (p) via the N 2 O 5 hydrolysis pathway may be significant in the aloft RL in other regions with similar geographical and meteorological conditions, such as Salt Lake Valley, Utah (Kuprov et al, 2014;Baasandorj et al, 2017). However, in valley regions with lower NO x or O 3 the nocturnal P NO − 3 may be lower, thus limiting the importance of this pathway (Akira et al, 2005;Bigi et al, 2012). Among other factors, the extent to which nocturnal NO − 3 (p) formation occurs more so in the surface layer versus in layers aloft will depend importantly on the extent of NO x emissions at the surface (which titrate O 3 , suppressing particulate nitrate formation), the absolute and relative height of the nocturnal boundary layer (which affects the rate of HNO 3 deposition and the air volumes in which nitrate production occurs), and gradients in RH, T and NH 3 (Kim et al, 2014).…”

The dispersion characteristics of air pollution from the world's megacities

“…Among the European megacities the Po Valley shows a unique behavior since the tracer is trapped there by mountains on three sides, which strongly limits the early phase of transport. One consequence of this is the high pollution levels usually registered in this area (e.g., Bigi et al, 2012). However, overall in the NH the megacity with the slowest horizontal transport up to 10 days is the tropical city of Lagos, which also has severe air pollution problems (Baumbach et al, 1995).…”

Governing processes for reactive nitrogen compounds in the European atmosphere

“…Often the morning rush hour is more pronounced than the afternoon rush hour, and this is reflected in emissions and resulting concentrations of NO x Menut et al, 2012). In some parts of Southern Europe there may even be four rush hours or a generally elevated traffic flow throughout the daytime hours (Bigi et al, 2012; as people are off work in the middle of the day.…”

“…Furthermore, different patterns are observed for weekday vs. weekend, and the pattern also differs for passenger cars and commercial vehicles Bigi et al, 2012;Vignati et al, 1996). Various studies have focussed on how to change transportation habits in urban areas, encouraging bicycle use, and discouraging rush-hour commuting (Murtagh et al, 2012;Su and Zhou, 2012;Zhao et al, 2012;Zhou, 2012).…”