During the last decade, the usefulness of passive mobile phone data for the study of urban mobility have been investigated by different research communities. Mobile phone data have many advantages, among them, a passive collection process and the availability of mobility data during a continuing period. However, at the moment in European Union due to an increasing concern in privacy issues, these data are aggregated per hour and antenna. We assume that this kind of data, despite their aggregation level, have still a large utility in studying urban mobility. To answer this issue we use a 12 months mobile phone dataset from the french mobile operator Orange. We will explore with visual and statistical methods Paris daily patterns in order to track differences between casual days and the massive alternate circulation day setup in march 2015 by local authorities, due to an historical pollution episode. Although the number of mobile phone users remains roughly constant, we assume that locally there will be some differences – due for example to an increase in telecommuting or public transportation use – showing the impact of such public policies on urban organization.