Synoptic weather patterns associated with carbon dioxide levels in Northern Spain

Measurements of atmospheric carbon dioxide, CO₂, were continuously carried out in the upper Spanish plateau over a three-year campaign, 2003-2005. Temporal CO₂ variations were examined. The results allow identification of the average data representative of background conditions, 382.9 ppm, with values ranging from 346.2 to 502.5 ppm. The weekly cycle evidences a difference of 0.2 ppm between weekday and weekend residuals, with levels increasing during the week. Seasonal variation in monthly means was inferred, the largest peak in appearing in spring, about 388 ppm. High values were also recorded in autumn, particularly in 2005 with an additional 5 ppm. By contrast, minimum values were obtained in July, between 374 and 379 ppm.A link between CO₂ concentrations and meteorological variables is explored. Analysis of surface wind speed intervals shows that low winds are the most frequent and are linked to the highest concentrations, around 395 ppm at night and in spring. CO₂ concentrations drop significantly for the 3.1-5.3 m s^− 1 interval from which steady levels, around 378 ppm except in autumn, were observed. If different temperature intervals are considered, the 10-15 °C interval establishes the boundary between the extreme mean CO₂ levels, except for winter, 5-10 °C. The mean associated values ranged between 376.0 and 390.4 ppm, with a greater contrast in spring, 12.8 ppm.Finally, the relation between synoptic-scale atmospheric transport patterns and maximum CO₂ concentrations was also examined. The highest values occur in spring with some quite frequent synoptic situations: continental ridges, troughs to the west, interactions of the two and Atlantic ridges.