A five‐year study of coastal recirculation and its effect on air pollutants over the East Mediterranean region

Abstract

[1] Many studies have shown that air pollutants concentrations in coastal cities may be gravely affected by coastal recirculation. In this study an attempt is made to examine the properties of coastal recirculation over a long period (5 yrs) at multiple sites along the East Mediterranean Sea (EMS). For this purpose, a single station quantitative measure of horizontal recirculation is used based on wind field measurements over periods of 1-96 hrs. The horizontal recirculation is examined with respect to the integration time period, synoptic flow, seasonality, coastline variations, elevation, and air pollutants concentrations. The interaction between synoptic and mesoscales is shown to be a governing factor by allowing or overruling the land sea breeze winds. Favorite conditions for coastal recirculation are shown to be light or variable winds such as under a Cole or a High-Pressure system. The monthly distribution of the recirculation potential has a bimodal behavior with two peaks during the transitional seasons and October in particular. This is as a result of the annual cycle of night-time land-sea temperature difference driving the land breeze and the more frequent passage of synoptic scale flows with an easterly wind component at the EMS. Two factors leading to variations along the coastline are the urban heat island, weakening the breeze winds and reducing recirculation potential, and the concaved shape of the southern shoreline that causes a convergence and strengthening of the land breeze, thus supporting recirculation. The primary pollutants NO x and SO 2 have the highest concentrations during weak daily mean wind speeds. O 3 levels depict an almost opposite image of NO x , with higher values for both high and low recirculation, possibly resulting from either long range transport or coastal recirculation.Citation: Levy, I., U. Dayan, and Y. Mahrer (2008), A five-year study of coastal recirculation and its effect on air pollutants over the East Mediterranean region,

Analyzing coastal precipitation using TRMM observations

“…During the rainy months studied here (November-March), EM Sea Surface temperatures are usually warmer than the adjacent land by 2-10 • C, making LB a common phenomena during the winter (Neumann, 1951;Goldreich, 2003;Levy et al, 2008). The LB magnitude varies both diurnally: maximum (minimum) Land-Sea Temperature Difference (LSTD) at sunrise (afternoon), and seasonally: maximum (minimum) LSTD during December (March).…”

“…1.1). Ground based radar observations near the Israeli coastline show a 1:1 to 3:1 sea to land rainfall ratio during winters (Levin et al, 2004), with the ratio peak in November, suggesting a stronger contribution of LB in the early stages of winter. Further evidence for LB effect is manifested through diurnal variation of lightning activity (Altaratz et al, 2003), showing a clear maximum of flashes number over sea (land) during midnight (afternoon).…”

Air recirculation and ventilation in the coastal regions of the Black Sea

“…pieces of work showed a good correlation between the recirculation parameter and the pollutant concentrations and confirmed the effectiveness of R. The authors [16] have shown that the integration period of 24 hours is optimal for recirculation assessment, regardless of the start time of integration and weather patterns. Our results are obtained by integrating over 24 hours, starting at 0 hours.…”

“…A lot of investigations [6,12,14,16,19,22,30] were devoted to the assessment of such conditions using Rand accompanied by measurements of the concentration of pollutants. These Table 1).…”

“…Active air recirculation in the breeze cell can lead to the accumulation of substances released during the day at the coast, decreasing air quality. [1,2,4,6,9,11,16,19].…”