Although emissions have a direct impact on air pollution, meteorological processes may influence inmission concentration, with the only way to control air pollution being through the rates emitted. This paper presents the close relationship between air pollution and meteorology following the scales of atmospheric motion. In macroscale, this review focuses on the synoptic pattern, since certain weather types are related to pollution episodes, with the determination of these weather types being the key point of these studies. The contrasting contribution of cold fronts is also presented, whilst mathematical models are seen to increase the analysis possibilities of pollution transport. In mesoscale, land–sea and mountain–valley breezes may reinforce certain pollution episodes, and recirculation processes are sometimes favoured by orographic features. The urban heat island is also considered, since the formation of mesovortices determines the entry of pollutants into the city. At the microscale, the influence of the boundary layer height and its evolution are evaluated; in particular, the contribution of the low-level jet to pollutant transport and dispersion. Local meteorological variables have a major influence on calculations with the Gaussian plume model, whilst some eddies are features exclusive to urban environments. Finally, the impact of air pollution on meteorology is briefly commented on.

Wind resources are increasingly being investigated as a clean alternative for generating energy. This paper analyses the daily wind speed recorded at 46 automatic weather stations located in Navarre, northern Spain, in 2005e2015. Key points are the surface density of stations and the range of time that ensure a faithful depiction of wind speed together with surface calculations from image analysis and correlation with height. Different statistics were used. Median wind speed at 10 m was low, about 3.3 m s À1 and its interquartile range was narrow, about 2.3 m s À1. Nearly half the surface shows a median wind speed above 3.0 m s À1. The method of moments was employed to calculate the parameters of the Weibull distribution. Around half of the surface presented a shape parameter above 2.25 and the scale parameter was above 4 m s À1 for nearly 41% of the region. Although wind resources are not suitable for wind turbine applications in most of the region, since the wind speed is low in low-lying areas, about 12% of the region is suitable for stand-alone applications and, moreover, a substantial part of the region, around 23%, presents satisfactory wind resources for the installation of wind turbines.

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CO and CH evolution is usually linked with sources, sinks and their changes. However, this study highlights the role of meteorological variables. It aims to quantify their contribution to the trend of these greenhouse gases and to determine which contribute most. Six years of measurements at a semi-natural site in northern Spain were considered. Three sections are established: the first focuses on monthly deciles, the second explores the relationship between pairs of meteorological variables, and the third investigates the relationship between meteorological variables and changes in CO and CH. In the first section, monthly outliers were more marked for CO than for CH. The evolution of monthly deciles was fitted to three simple expressions, linear, quadratic and exponential. The linear and exponential are similar, whereas the quadratic evolution is the most flexible since it provided a variable rate of concentration change and a better fit. With this last evolution, a decrease in the change rate was observed for low CO deciles, whereas an increasing change rate prevailed for the rest and was more accentuated for CH. In the second section, meteorological variables were provided by a trajectory model. Backward trajectories from 1-day prior to reaching the measurement site were used to calculate distance and direction averages as well as the recirculation factor. Terciles of these variables were determined in order to establish three intervals with low, medium and high values. These intervals were used to classify the variables following their interval widths and skewnesses. The best correlation between pairs of meteorological variables was observed for the average distance, in particular with horizontal wind speed. Sinusoidal relationships with the average direction were obtained for average distance and for vertical wind speed. Finally, in the third section, the quadratic evolution was considered in each interval of all the meteorological variables. As regards the main result, the greatest increases were obtained for high potential temperature for both gases followed by low and medium boundary layer height for CO and CH, respectively. Combining both meteorological variables provided increases of 22 ± 9 and 0.070 ± 0.019 ppm for CO and CH, respectively, although the number of observations affected is small, around 7%.

This work analyses levels of particles PM10 and PM2.5 recorded at four air-quality monitoring stations located in the urban area of Valladolid (Spain) during 2015-2016. To achieve this, the evolution of particle concentrations at different time scales was determined. Average concentrations ranged from 15.3 to 17.6 µg m −3 for PM10 and between 8.9 and 14.8 µg m −3 for PM2.5. The highest monthly means were recorded in autumn and winter. The difference between mean concentrations at weekends and on weekdays for PM10 was around 3 µg m −3 at most of the measuring stations and was 1 µg m −3 for PM2.5. Two concentration peaks were found during the day, one in the morning and the other in the evening, which evidenced the influence of traffic and other anthropogenic activities on PM concentrations. Their mean values were approximately 21 and 17-21 µg m −3 , respectively, for PM10. Mean maximum values for PM2.5 were 12 µg m −3 , except at one of the measuring sites, with 17 µg m −3 for the morning maximum and 1 µg m −3 more for the nocturnal peak. In addition, the impact of longdistance transport of air masses in the study area was analysed by applying a HYSPLIT trajectory model, taking into account backward trajectories of European, African, and Atlantic origins as well as local conditions. In particular, high concentration events due to Saharan dust intrusions are presented. Finally, background levels of particle concentrations estimated at most sampling areas were around 15 and 7.7 µg m −3 for the PM10 and PM2.5 particle fractions, respectively.