Exploring wind direction and SO2 concentration by circular-linear   density estimation
  The study of environmental problems usually requires the description of variables with different nature and the assessment of relations between them. In this work, an algorithm for flexible estimation of the joint density for a circular-linear variable is proposed. The method is applied for exploring the relation between wind direction and SO2 concentration in a monitoring station close to a power plant located in Galicia (NW-Spain), in order to compare the effectiveness of precautionary measures for pollutants reduction in two different years. 
Eduardo Garc\'ia-Portugu\'es, Rosa M. Crujeiras, Wenceslao   Gonz\'alez-Manteiga
stat.ME