Day-night variability of PM10 components at a Mediterranean urban site during winter

Daytime and nighttime PM₁₀ samples were collected during winter at an urban site in Southeastern Spain. Samples were subsequently analyzed to determine the concentrations of water-soluble ions, carbonaceous species, and metals. PM₁₀ daytime and nighttime concentrations were 26.1 and 20.6 μg/m³, respectively. This difference may be mainly attributed to the reduction in the number of vehicles during nighttime. Traffic-related components such as EC, Ca and other crustal elements, Cu or Zn, showed statistically significantly higher concentrations during daytime, suggesting that traffic emissions were more relevant than day-to-night differences in meteorological conditions. In contrast, no significant differences between daytime and nighttime levels of secondary inorganic ions (SO₄^2?, NO₃^? and NH₄⁺) were found. Primary and secondary organic carbon concentrations were estimated using the EC tracer method. As expected, POC levels were greater during the day due to increased vehicle exhaust emissions; conversely, higher SOC concentrations were registered during the nighttime period. This was most likely the result of a significant contribution of nighttime chemistry to the formation of secondary organic aerosols.