Menachem Luria

Heterogeneous sulfur conversion in sea-salt aerosol particles: the role of aerosol water content and size distribution

Abstract Meteorological and chemical conditions during the July 1988 Bermuda-area sampling appear to have been favorable for conversion of sulfur gases to particulate excess sulfate (XSO4). Observed average XSO4 and SO4 concentrations of 11 and 2.1 nmol m−3, respectively, at 15 m a.s.l. in the marine boundary layer (MBL) upwind of Bermuda, indicate that conversion of SO2 to XSO4, over and above homogeneous conversion, may be necessary to explain the > 5.0 average molar ratio of XSO4 to SO2. Given an observed cloud cover of Aerosol water content, estimated as a function of particle size distribution plus consideration of SO2 mass transfer for the observed particle size distribution, shows that SO2 was rapidly transferred to the sea-salt aerosol particles. Assuming that aqueous-phase SO2 reaction kinetics within the high pH sea-salt aerosol water are controlled by O3 oxidation, and considering mass-transfer limitations, SO2 conversion to XSO4 in the sea-salt aerosol water occurred at rates of approximately 5% h−1 under the low SO2 concentration, Bermuda-area sampling conditions. All of the 2 nmol XSO4 m−3 associated with sea-salt aerosol particles during low-wind-speed, Bermuda-area sampling can be explained by this conversion mechanism. Higher wind speed, greater aerosol water content and higher SO2 concentration conditions over the North Atlantic are estimated to generate more than 4 nmol XSO4 m−3 by heterogeneous conversion of SO2 in sea-salt aerosol particles.

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.

Heterogeneous and homogeneous oxidation of SO2 in the remote marine atmosphere

Abstract A photochemical computer model was used to simulate production and removal of S-containing species in the remote marine atmosphere. The results of aircraft and shipboard trace gas and aerosol measurements, performed during the 1988 Coordinated Air-Sea Experiment/Western Atlantic Ocean Experiment (CASE/WATOX) were used for the model input. The modeling revealed that homogeneous oxidation can not explain the existence of excess sulfate on large particles. Thus, it must be supplemented by an additional process in order to obtain a balance between sources and sinks of sulfur species. A proposed heterogeneous pathway consisting of SO 2 condensation on and oxidation in aerosol particles was tested. With the addition of the heterogeneous processes, and assuming that the rate-determining step is condensation of SO 2 on large particles by molecular diffusion, it was possible to simulate the experimentally observed concentrations of all sulfur species. Results show that the upper limit for rate constants (dictated by diffusion theory) was 50–1500 times larger than the rate constants used in the model for the condensation process. The balance between sources and sinks, using this model, requires that nearly 60% of the observed oxidation should occur via the heterogeneous channel at a rate of about 0.015 h −1 . The 24h average homogeneous rate was approximately 0.01 h −1 .

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.

Relative production of ozone and nitrates in urban and rural power plant plumes: 1. Composite results based on data from 10 field measurement days

A rather limited number of large power plants are responsible for about 2/3 and 1/3 of the U.S. anthropogenic emissions of SO2 and NOx, respectively. Considerable uncertainty continues to prevail about the local and regional impact of their potentially harmful secondary products (e.g., ozone, sulfates, nitrates), We have analyzed state-of-the-art data of the Southern Oxidant Study (SOS)-Nashville Field Study (1994, 1995) for 10 days of summer daytime field measurements by instrumented aircraft in the plumes of three large, tall-stack, base-load, Tennessee Valley Authority (TVA) coal-fired power plants in northwestern Tennessee: Gallatin (G), located within the Nashville urban ozone nonattainment area, and Cumberland (C) and Johnsonville (JV) in rural isoprene-rich forested areas about 100 km to the west of Nashville. The average 1995 emissions of NOx from these three sources ranged over more than an order of magnitude. In this paper, we have explored plume chemical evolution and the magnitude, efficiency, and yield of ozone and NOz, (NOx oxidation products, mostly inorganic and organic nitrates) production in a broad variety of plume transport and chemistry scenarios within the convective boundary layer (CBL) in rural and urban settings. The results show that (1) plume chemical maturity and peak production capacities of ozone and NOz were realized quite close to the sources, within 30–40 km and 4 hours of daytime transport for Gallatin (smallest NOx emission rate, QNOx, and suburban environment) and typically within 100 km and 6 hours of CBL transport for Cumberland (highest QNOx and rural environment rich in isoprene); (2) the ozone impact of Gallatin on Nashville can exceed that of Cumberland, and under favorable transport and chemical conditions, both power plants can contribute as much as 50 ppb of excess ozone to the urban area, raising local peak levels well in excess of 100 ppb; (3) an estimated 3.1±0.7 molecules of ozone and more than 0.6 molecules of NOz, may be produced in large isolated rural power plant plumes (PPPs) per molecule of NOx release, and the corresponding peak yields of ozone and NOz may be significantly greater in urban PPPs; (4) the rate of NOz production ≈ 10–15% h−1 in isolated rural PPPs, and higher in urban PPPs; (5) NOz production is favored in all PPPs at first when the chemistry is VOC-limited; later, with increasing VOC ingestion from the background, the chemistry increasingly favors NOx-limited ozone production, starting at plume edges, and ultimately throughout the diluted plume. These results have major implications on outstanding issues related to the environmental impact and regulatory control of electric utility industry NOx emissions.

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.

The production of O3 in an urban plume: Airborne sampling of the Atlanta urban plume

Abstract As part of the Southern Oxidant Study, The Tennessee Valley Authoritys instrumented helicopter made a series of air sampling flights over the city of Atlanta. The flights were made during the summer of 1992 to investigate the evolution of the urban O 3 plume. Air samples were taken during morning and afternoon hours; the morning data were used to estimate background O 3 and the afternoon data were used to estimate O 3 production efficiency, i.e. the number of O 3 molecules produced per molecule of NO y emitted. Detailed data on O 3 production were available for five afternoon flights. Within the radius sampled, three zones were identified: the source zone where afternoon levels were comparable with the morning levels, the production zone where 03 increased rapidly within a short distance, and the dilution zone where both O 3 and its precursors were diluted, at the same rate. O 3 peak levels, or the transition from net production to dilution occurred at 20–40 km from the city center. O 3 production efficiency for the five afternoon flights was between 4 and 10, in good agreement with previous surface measurements.

The relationship between dimethyl sulfide and particulate sulfate in the mid-atlantic ocean atmosphere

Abstract Dimethyl sulfide (DMS) and atmospheric aerosols were sampled simultaneously over the Atlantic Ocean in the vicinity of Bermuda using the NOAA King Air research aircraft. Total and fine (50% cutoff at 2 μm diameter) aerosol fractions were sampled using two independent systems. The average nonsea-salt (nss)SO 4 2− concentrations were 1.9 and 1.0 μg m −3 (as SO 4 2− ) for the total and the fine fractions in the boundary layer (BL) and 0.53 and 0.27 μg m −3 in the free troposphere (FT). Non-sea-salt SO 4 2− in the two aerosol fractions were highly correlated ( r = 0.90), however a smaller percentage (55%) was found in the fine aerosol near Bermuda relative to that (90%) near the North American continent. The BL SO 4 2− concentrations measured in this study were higher than those measured by others at remote marine locations despite the fact that the 7-day air mass back trajectories indicated little or no continental contact at altitudes of 700 mb and below; the trajectories were over subtropical oceanic areas that are expected to be rich in DMS. DMS concentrations were higher near the ocean surface and decreased with increasing altitude within the BL; the average DMS concentration was 0.13 μg m −3 . Trace levels of DMS were also measured in the FT (0.01 μg m −3 ). Computer simultation of the oxidation and removal of DMS in the marine atmosphere suggests that 4 2− observed could be related to the natural S cycle.

O3, CO, Hydrocarbons and dimethyl sulfide over the Western Atlantic Ocean

Abstract The concentrations of O 3 , CO, dimethyl sulfide (DMS) and light hydrocarbons (C 2 –C 4 ) were measured from an instrumented aircraft during February–April 1985, near the U.S. East Coast and in the vicinity of Bermuda as part of the Western Atlantic Ocean Experiment (WATOX). Sampling flights were performed within the boundary layer (BL) and in the free troposphere (FT) at both locations. Photochemical generation of O 3 in polluted air parcels transported from the continent within the BL was identified as the probable source of excess O 3 (up to 50 ppbv above background). Convective lifting of boundary layer air carried pollutants into the free troposphere. The concentrations of HC compounds in air sampled near Bermuda had a significant inverse relation to air mass transport time from the continent. The BL concentrations of the more reactive HCs (ethylene, propane, propylene, normal- and isobutane) declined faster than the less reactive HCs (acetylene and ethane), and were found to be proportional to air mass transport time over the ocean. DMS was detected, with few exceptions, only within the BL at both sampling locations. The average concentrations in the BL samples collected near the U.S. East Coast and in the vicinity of Bermuda were 27 and 54 pptv. In all samples taken in the BL the DMS concentration decreased sharply as a function of altitude.