The influence of meteorological conditions and atmospheric circulation types on PM₁₀ and visibility in Tel Aviv

A 3-yr dataset (February 2000-November 2002) of 30-min averages for particulates, visibility, and meteorological data were analyzed to examine the dependence of particulate matter of less than 10 μm in diameter (PM₁₀) mass concentrations and visibility in Tel Aviv, Israel, on seasonal meteorological conditions, synoptic weather patterns, and airmass history. The persistent nature of the summer synoptic weather pattern in the east Mediterranean (EM) region yielded the highest mean visibility (35 km) and lowest variability in PM₁₀ concentrations, as compared with the higher variance for the other seasons, and spring in particular. The frequent passage of the "Sharav" cyclones during spring causes natural dust outbreaks with extreme values that result in a much higher PM₁₀ annual mean (57 μg m^-3) as compared with other larger cities. The history of the air mass dictating the physical and chemical properties of the particulate matter reaching Israel was assessed by back-trajectory analysis from predetermined transport sectors. The west and central European sectors, representing mostly the summer flow regime of European clean air masses that are advected over the Mediterranean, differ significantly in their reduced PM₁₀ loading and high visual range from the Arabian Peninsula and North African sectors, originating from the surrounding deserts. Because the most frequent direction of air masses reaching the EM is from European origins, Tel Aviv experiences most of the time satisfying visibility conditions. Applying the definition "very good visibility" for visibility exceeding 19 km shows that about 90% of the time these conditions were met for this 3-yr period.