Mordechai Peleg

Atmospheric sulfur over the east Mediterranean region

Particulate sulfate has been measured intermittently at various ground sites in Israel and from an instrumented aircraft for a 10-year period between 1984 and 1993. The measurements were accompanied by concurrent monitoring of primary and secondary air pollutants and meteorological parameters. In three studies, Etzion 1984–1986, Jerusalem 1987–1988, and Jerusalem 1990–1991, measurements were taken for at least a year. The other studies were performed during summer months when higher levels of secondary pollutants, including particulate sulfate, were observed. In most of the studies samples were taken for four sequential 6-hour time segments. In one study, at Caesarea 1993, sulfate samples were taken only when wind flows were perpendicular to the coastline. The airborne measurements were performed along three north-south paths inside the planetary boundary layer, over the Mediterranean coast, over the Judea-Samaria mountains and over the Jordan Valley. Each flight path consisted of 30 to 45 minutes of continuous sampling of SO2 and one integrated sample of particulate sulfate. In all of our studies the concentration of particulate sulfate observed was relatively high compared with other world locations. The highest values, occasionally exceeding 500 nmole m−3, were found during the summer. Wintertime levels were in the range of 50–100 nmole m−3. The annual average, calculated for the three long studies, is 100 ± 15 nmole m−3, which is twice as high as predicted for the region by a global model and as high as reported for some of the more polluted regions in the US. Several indicators suggested that the origin of the sulfate in the region is not from local sources but the result of long range transport. The indicators include the lack of correlation between particulate sulfate and primary pollutants, the high sulfate to total sulfur values, the origin of the airmass back trajectories and the fact that similar levels were observed during concurrent periods at different sites. Throughout the study, higher concentration of particulate sulfate was found during the afternoon hours, especially during the summer and at the inland locations. The contribution to the afternoon elevated values could not be associated with long range transport and results probably from major sulfur emission sources located along the Israeli Mediterranean coast.

Bromine oxide—ozone interaction over the Dead Sea

Atmospheric measurements were performed during a 1 month period in early summer of 1997 at the Dead Sea in Israel in an attempt to identify bromine monoxide BrO, and evaluate its effect on ozone chemistry. The differential optical absorption spectroscopy (DOAS) technique was utilized to identify and measure BrO present in the air masses. Concurrent to the DOAS measurements, continuous monitoring of SO2, NO/NOx, O3, and CO was performed. Filter samples for aerosol analysis and whole air canister samples for bromocarbon analysis were also collected. The present paper reports the complete comprehensive data set of the measurements at the Dead Sea site and is a continuation to our preliminary communication [Heberstreit et al., 1999]. The more complete data now available enable a more detailed examination of the sources and mechanisms of the reactive halogen species and the presentation of new conclusions. The results showed a diurnal repeating cycle of O3 and BrO variations, correlated with solar radiation and wind direction. During the elevated BrO events, where bromine oxide rose to daily maximum values often exceeding 100 ppt, a clear negative correlation with O3 was observed. During these episodes, the O3 regularly decreased from noontime levels of 50–80 ppb or higher down to 10–30 ppb and occasionally to levels below the detection limit of 2 ppb. The enhanced BrO levels were associated with southerly winds that are typical for the location during midday hours. This suggests that a possible source for the reactive bromine species is the interaction of atmospheric oxidants with bromide at the surface of the large salt pans located at the southern end of the Dead Sea. Research flights flown over the area showed that ozone destruction to levels well below the background values were observed over large areas of the Dead Sea Valley.

Recirculation of polluted air masses over the East Mediterranean coast

Abstract An air quality observatory was operated at a rural site on the Mediterranean coast of Israel near the ancient city of Caesarea between May 1993 and October 1995. The objective of the study was to monitor transport of air pollutants from remote sources that arrive at the Israeli coast. Normally, under onshore westerly winds, which come from the Mediterranean sea, the levels of NO, NOy and SO2 at the site dropped to below 0.5 ppbv, CO to below 150 ppbv, and the O3 levels ranged between 30 and 60 ppbv. During the last week of October 1993, an unusual series of pollution episodes occurred, with elevated values for all the pollutants being recorded during onshore flows. The SO2 concentration reached 30 ppbv, NO and NOy more than 100 ppbv and O3 levels rose above 200 ppbv. On 26 October the O3 levels were the highest observed with an abnormally high concentration of 230 ppbv being recorded. The episode that occurred on that day was investigated in detail in order to understand the cause for this high ozone value. During the above day, night and early morning, easterly winds swept the air parcels containing the locally emitted pollution westwards over the sea. The intense photochemical activity that occurred while the air mass was over the sea for a relatively extensive time combined with the low mixing height on that day and the fact that the returning air mass reached the measuring site at peak ozone formation time, give rise to record ozone levels. The elevated concentrations were measured when the polluted air parcels returned to the coast during the afternoon onshore flows. An excellent linear correlation between O3 and NOy was obtained for the time period between 1400 and 1700. The linear fit between O3 and NOy indicates that approximately 11 O3 molecules were formed for each NOy molecule present. Similar ratios have been reported in other studies dealing with aged air masses under NOy limited conditions.

Some observational and modeling evidence of long-range transport of air pollutants from Europe toward the Israeli coast

The present paper reports results of a study that attempted to elucidate the factors causing relatively high levels of particulate sulfate that have frequently been observed over central Israel. Aircraft research flights were performed some 70 km west of and parallel to the Israeli coastline during September 1993 and June 1994. Comparison between the two measurement periods revealed a distinctive difference between the two different sampled air masses. While both air masses were nearly homogeneous throughout the measurement period and along the 180 km flight path, the air mass sampled in September 1993 was much cleaner than the air mass sampled during June 1994. The concentrations of the air pollutants measured during the 1993 campaign averaged 0.7 ± 0.4 parts per billion by volume (ppbv) SO 2 , 1.0 ± 0.6 ppbv NO y , 39 ± 7 ppbv O 3 and 38 ± 7 nmol/m 3 particulate sulfate, whereas in the second period the levels averaged 3.0 ± 1.0, 3.9 ± 1.8, 48 ± 9, and 108 ± 63, respectively. These results suggest that the two air masses traveled different paths before reaching the eastern Mediterranean region. Further examination of the air mass sources and transport were performed using the Regional Atmospheric Modeling System for meteorological simulations and the Hybrid Particle and Concentration Transport Package for dispersion modeling. The model simulation showed that during the 1993 measurement period, the pollution sources in southern Europe and the Balkans did not effect the eastern coasts of the Mediterranean, while the synoptic conditions and simulation results for the June 1994 period indicated that the winds over the eastern Mediterranean tended to be northwesterly and thus forcing the polluted air masses toward the coast of Israel.

Atmospheric sulfur flux rates to and from Israel

Both field measurements and model simulation studies have shown that Israel is the recipient of long range transported air pollutants that originated over various parts of Europe. The present paper presents results of aircraft measurements aimed at quantitizing the sulfur flux arriving at Israels western coast from Europe and the Israeli pollution contribution to the air masses leaving its eastern borders towards Jordan. During the research flights, measurements of sulfur dioxide and sulfate particulates and meteorological data were recorded. Two different legs were performed for each research flight: one over the Mediterranean Sea, west of the coast and the second along the Jordan Valley. All flights were carried out at a height of approximately 300 m above ground level. A total of 14 research flights were performed covering the summer and autumn seasons. The results indicate that the influx of sulfur arriving at the Israeli coast from Europe varied in the range of 1-30 mg S/h, depending on the measuring season. The particulate sulfate level in the incoming LRT air masses was at least 50% of the total sulfur content. The contribution of the local pollutant sources to the outgoing easterly fluxes also varies strongly according to season. During the early and late summer, the Israeli sources contributed an average of 25 mg S/h to the total pollution flux as compared to only approximately 9 mg S/h during the autumn period. Synoptic analysis indicates that conditions during the summer in Israel favor the accumulation of pollution species above the Mediterranean basin from upwind European sources. This season features a shallow mixed layer and weak zonal flow leads to poor ventilation rates, inhibiting an efficient dispersion of these pollutants while being transported eastward. Under these conditions, in flux, local contribution and the total out-flux of these pollutants are elevated as opposed to during other seasons. During the fall, the eastern Mediterranean region is usually subjected to weak easterly winds, interrupted at times by strong westerly wind flows inducing higher ventilation rates. These meteorological conditions and the lack of major emitting sources eastwards of Israel result in lower sulfur budgets to and from Israel for this season. An estimate of the yearly flux showed that approximately 0.06 tg S arrived at the Israeli coast from the west. This is approximately 15% of the estimated pollution leaving Europe towards the eastern edge of the Mediterranean basin. The local contribution to the out-flux towards Jordan was calculated to be 0.13 tg S per year, almost all of the sulfur air pollutants emitted in Israel.

Observational evidence of an ozone episode over the Greater Athens Area

Research flights have been performed over the Greater Athens Area (GAA) and southwards over the Island of Aegina and east of Peloponnisos in order to investigate the evolution of an ozone episode over GAA and the transportation of the urban pollution plume southwards from the Athens region. During the 3 day period of 6 July to 8 July 1994, the GAA was under the influence of an ozone episode with ground-level noontime concentrations of more than 120 ppbv. Upper-air ozone concentrations measured during the flights were as high as 135 ppbv. The interaction of the weak synoptic conditions over the area along with the development of a mesoscale thermal circulation created poor dispersion conditions during the period of interest and resulted in elevated ozone levels. The primary pollutants emitted in the GAA during the night and early morning hours, were funneled out to the Saronic Gulf and southwards along the southwestern Aegean Sea, near the coast of east Peloponnisos. Under the influence of strong sunlight these primary pollutants continued to undergo photochemical reaction giving rise to elevated ozone levels tens of kilometers downwind of the pollution emission sources. Further evidence of the photochemically-aged air masses was the high correlation (R2 = 0.8) observed between NOy, and ozone. The ozone production efficiency in these transported air masses reached a value of close to six.

CO and NOx levels at the center of city roads in Jerusalem

Abstract CO and NOx monitors in conjunction with a data acquisition system were installed inside a small van, together with an independent battery operated power supply, to study air pollution levels in the zones where Jerusalem commuters are exposed. The results revealed that along most sections of the test road, CO and NOx concentrations exceed the short term lower Israeli national air quality standards of 30 and 0.5 ppm, respectively. In addition, there were also a large number of violations of the higher standard for NOx (1.0 ppm). Traffic volume correlated reasonably well with pollution levels; however, the geometry of the road was found to be equally important. The highest pollution levels were recorded in the narrower segment of the test road near the market place, despite the fact that the traffic counts along these road segments were relatively low. This phenomenon is related to the trapping caused by the canyon effect resulting from the buildings bordering the road. No significant relationship with the general meteorological conditions was found, however, rain washout of NOx was observed during one sampling trip, while CO concentrations ramained almost unaffected.

Long-term measurements of NO3 radical at a semiarid urban site: 2. Seasonal trends and loss mechanisms.

This study is the first to present long-term measurements of the nitrate radical in an urban location. Extensive nitrate radical measurements were conducted together with ancillary parameters during a continuous two year campaign (2005-2007) in the semiarid location of Jerusalem. The average nighttime NO3 concentration was 27.3+/-43.5 ppt, the highest ever reported, with a seasonal average peak during summer (33.3+/-55.8 pptv) with maximum levels exceeding 800 pptv. Significant diurnal changes in NO3 concentrations were observed, caused by an unusual nighttime increase in ozone concentrations. The NO3 loss processes exhibited strong seasonal variability. Homogeneous gas-phase losses were the main removal processes during summer and spring. The heterogeneous losses of N2O5, averaged over the entire campaign, contributed to less than half of the direct losses even though they dominated the winter seasons and part of the autumn months. Statistical regression analysis showed that NO3 was inversely correlated with relative humidity and positively correlated with temperature and to a lesser extent with NO2 and O3, indicating that the heterogeneous removal processes were also important. The diurnal behavior of NO3 was examined using a one-dimensional chemical transport model. The simulations showed that NO3 trends and concentrations were influenced mainly by changes in ozone and nitrogen oxide levels and that the very high levels of NO3 can be explained by the entrainment of fresh ozone from the upper atmospheric levels. After sunset and in the early morning, the homogeneous processes are the major loss pathways, while the heterogeneous N2O5 removal pathway dominates the intermediate times.

Particulate sulfate levels at a rural site in Israel

Ambient particulate sulfate measurements have been intermittently performed at a rural site in Israel over a period of more than two years. Concurrent measurements of ambient pollutants (SO2, NO−NOx, and O3), as well as meteorological data, were also carried out. The daily data included four particulate sulfate samples representing four successive 6 h accumulating periods. The measured concentrations of sulfate ions ranged from a low 2 μg m-3 observed during the winter season to a high of >50 μg m-3 obtained during the summer. Little correlation was obtained between the sulfate concentration and either O3 or SO2, although sulfate and O3 showed a similar diurnal and annual trend. Based on the data distribution and on a photochemical model, it was concluded that a large part of the particulate sulfate observed at the eastern coast of the Mediterranean Sea must be related to long-range transport from distant sources.

Impact of coastal transportation emissions on inland air pollution over Israel: Utilizing numerical simulations, airborne measurements, and synoptic analyses

[1] The detection of high ozone levels over large inland areas in Israel during the early, mid and late summer triggered an analysis of air mass back-trajectories. This, in turn, pointed to the transportation system in the metropolitan coastal Tel Aviv region as the possible origin of the ozone’s precursors. To link the daily dynamics of rush hour transportation emissions to inland air pollution, in general, and airborne ozone measurements, in particular, an interdisciplinary modeling system was established. The simulations of transportation-to-inland air pollution integrated transportation, emission factor, atmospheric, transport/diffusion, and photochemical models. The modeling results elucidated a spatial and temporal overlap between the ozone precursors and ozone production. The model simulations indicated east to southeasterly dispersion of the pollution cloud. The results agreed well with both spatial and temporal ozone levels as recorded by aircraft over central Israel, as well as with ground-based monitoring station observations. The impact of the Tel Aviv metropolitan area as well as the Gaza Strip, as pivotal coastal transportation sources for inland air pollution in general and ozone formation in particular, is discussed. The synoptic analysis identified the conditions prevailing when elevated air pollution, and especially high ozone levels, exists over central Israel. The analysis showed that this season features a shallow mixed layer and weak zonal flow, which leads to poor ventilation rates and inhibit efficient dispersion of this secondary pollutant. These poor ventilation rates result in the slow transport of ozone precursors, enabling their photochemical transformation under intense solar radiation during their travel from the coast inland. Under these conditions, model results showed that traffic emissions during the morning rush hour from the Tel Aviv metropolitan area contribute about 60% to the observed ozone concentrations. INDEX TERMS: 0345 Atmospheric Composition and Structure: Pollution—urban and regional (0305); KEYWORDS: air pollution, numerical atmospheric modeling, transportation model, emission factors, photochemical model, ozone, photochemical aged air mass