Several European urban areas are characterised by low air quality due to high local emission per unit surface. A further key feature can be related to the pollutant load due to adverse local meteo-climatic conditions. This study aims to compare the two urban agglomerations of Torino and Lyon – located on opposite sides of the Alps and characterised by similar size and population – to enlighten the role of meteorology on local pollutant dispersion. The assessment of air quality has been developed by monitoring network data, emissions analysis and the SIRANE urban dispersion model. Although the two agglomerations have similar NO_X and PM10 emissions, the simulation results show higher ground level concentrations in Torino. To quantify the effect of meteorology on this excess of concentrations, we run simulations in Torino imposing the meteorological conditions of Lyon and vice versa. This implies an overall reduction of ground level concentrations in the city centre of Torino between 20% and 40% (analogously, Lyon concentrations increase by a similar amount). These results show the peculiar difficulties faced by Po valley's cities in maintaining pollution levels below regulatory thresholds and highlight the need of systemic policies and site-specific mitigation to reduce air pollution health risks.

欧洲的一些城市地区由于单位表面局部高排放而导致空气质量低下。另一个关键特征可能是由于不利的局部气象条件造成的污染物负荷。这项研究旨在比较都灵和里昂这两个城市群（都位于阿尔卑斯山的对面，并具有相似的规模和人口），以启发气象学在当地污染物扩散中的作用。通过监测网络数据，排放分析和SIRANE城市扩散模型，可以开发空气质量评估。尽管两个团块的NO _X相似和PM10排放，模拟结果显示都灵的地面浓度较高。为了量化气象对这种过量浓度的影响，我们在都灵进行了模拟，并提出了里昂的气象条件，反之亦然。这意味着都灵市中心的地平面浓度总体降低了20％至40％（类似地，里昂的浓度增加了类似的数量）。这些结果表明，波谷市在将污染水平保持在监管阈值以下方面面临着特殊的困难，并强调需要采取系统性政策和针对特定地点的缓解措施来减少空气污染健康风险。