Yitzhak Mahrer

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.

Predicting the microclimate inside a greenhouse: an application of a one-dimensional numerical model in an unheated greenhouse

Abstract A one-dimensional numerical model has been adapted to predict the microclimate inside an unheated commercial greenhouse during a continuous period of 51 days. The main outputs of the model (hourly air and leaf temperatures and relative humidity) were used to derive the leaf wetness duration (LWD) each day. Measured microclimate parameters inside the greenhouse were used to test the model performance during the corresponding period. Reasonable agreement was found between the predicted and measured parameters for the entire period. The root mean square differences between the predicted and actual air and leaf temperatures, relative humidity and LWD were 1.2 and 1.8°C, 5.8% and 1.9 h d −1 , respectively.

Modeling the Survival of Two Soilborne Pathogens Under Dry Structural Solarization

ABSTRACT Structural (space) solarization of a closed, empty greenhouse for sanitation involves dry heating to 60 degrees C and higher and low relative humidity (RH), under a fluctuating temperature and RH regime. Survival of inocula of Fusarium oxysporum f. sp. radicis-lycopersici and Sclerotium rolfsii during structural solarization was studied for 4 years (total of 12 experiments) in an attempt to develop a dynamic model for expressing the thermal inactivation of the pathogens. After 20 days of exposure, the populations of F. oxysporum f. sp. radicis-lycopersici and S. rolfsii were reduced by 69 to 95% and by 47.5 to 100%, respectively. The Weibull distribution model was applied to describe pathogen survival. The Weibull rate parameter, b, was found to follow an exponential (for F. oxysporum f. sp. radicis-lycopersici) and the Fermi (for S. rolfsii) functions at constant temperatures. To improve the applicability of the model, fluctuating conditions of both temperature and RH were utilized. The Weibull distribution derivative, expressed as a function of temperature and moisture, was numerically integrated to estimate survival of inocula exposed to structural solarization. Deviations between experimental and calculated values derived from the model were quite small and the coefficient of determination (R (2)) values ranged from 0.83 to 0.99 in 9 of 12 experiments, indicating that ambient RH data should be considered. Structural solarization for sanitation could be a viable component in integrated pest management programs.

Effects of air temperature, relative humidity and canopy wetness on gray mold of cucumbers in unheated greenhouses.

Microclimatic variables were monitored in cucumber crops grown in polyethylene-covered, unheated greenhouses in Israel during the winter of 1987/88. The winter was characterized by a relatively large number of rainy days. The relative humidity (RH) in the greenhouses was high (>97%) during most of the day, resulting in long periods of dew persistence. Dew point temperature and duration of dew deposition were calculated for the plant canopy. Disease incidence was monitored in 2-m-high plants, both on senescing female flowers (‘fruits’) and on stems. Multiple linear correlations were calculated for gray mold incidence and duration of air temperature and RH at specific ranges, and of leaf wetness (LW). Disease was characterized by two stages, according to the rate of its development and the microclimatic conditions influencing it. In the first phase of the epidemic a high correlation was found between infected fruits and air temperature in the range of 11–25°C, and RH in the range of 97–100% or LW. In the second phase, disease incidence was better correlated with air temperature in the range of 11–16°C and RH above 85% (R2 = 0.681); there was no correlation between disease and LW at this stage. Development of stem infections was correlated with air temperature in the range of 11–16°C during the first phase of the epidemic. By contrast, the second phase was characterized by a close correlation between stem infections and RH in the range of 80–100% but also with air temperature in the range of 11–16°C, or with air temperature in the range of 11–25°C and RH 80–100%, and LW.

Qualitative approach for modelling outbreaks of grey mould epidemics in non-heated cucumber greenhouses

Disease records and microclimatic parameters were analysed in order to develop a model for predicting outbreaks of grey mould (Botrytis cinerea) epidemics in non-heated cucumber greenhouses. A quantitative statistical approach failed to produce a reliable model. However, when employing a qualitative approach, an accurate, biologically sound prediction model was developed. Outbreaks of grey mould occurred when, on a weekly average, the wetting period of the foliage exceeded 7 h day−1 and the duration of temperature in the range of 9–21°C during the night (18:00–08:00) exceeded 9.5 h day−1. Data recorded in two growing seasons were used to construct the model and its predictions were evaluated with an independent data set. Controlled-environment experiments provided biological interpretations for these greenhouse-originated thresholds: when free moisture was present, germination of B. cinerea spores occurred within 7 h; the period during which the pathogen is exposed to environmental microclimatic influences (germination and penetration) is 9–10 h. The potential for outbreaks of grey mould epidemics in commercial greenhouses could be reduced by restricting the wetting period to <7 h day−1 by measures such as ventilation and heating.

Effect of moisture on thermal inactivation of soilborne pathogens under structural solarization

ABSTRACT Structural solarization of greenhouses for sanitation by closing them involves dry heating to 60 degrees C and higher with a consequent low relative humidity (RH) ( approximately 15%), thus requiring an extended period for thermal inactivation of pathogens. In an attempt to enhance pathogen control by increasing moisture during the hot hours of the day, various regimes of inoculum moistening were studied. However, wetting inoculum of Fusarium oxysporum f. sp. melonis and F. oxysporum f. sp. radicis-lycopersici resulted in less effective pathogen control compared with that of dry heating. Fifty percent effective dose (ED(50)) values of thermal inactivation of wetted and dry inoculum for the former pathogen were 18 and 7 days, respectively, and for the latter, a respective 9 and 4 days. This was because wetting resulted in inoculum cooling due to evaporation, which eventually led to its drying. A model describing the drying of wet inoculum in a wetted greenhouse, based on the fact that there was an approximately 10 degrees C difference between greenhouse and ambient temperatures, was proposed. A double-tent system reduced this difference to 1 to 2 degrees C, reduced moisture loss, and led to improved inoculum inactivation of F. oxysporum f. sp. radicis-lycopersici. Thus, the ED(50) value of thermal inactivation was reduced from 15 days to 1 day, because this system provided both high temperature ( approximately 60 degrees C) and high RH ( approximately 100%), resulting in effective wet heating.

Studying coastal recirculation with a simplified analytical land‐sea breeze model

[1] The diurnal cycle of the land and sea breeze is of high importance in determining many aspects of the living conditions in coastal areas. One of these aspects is the buildup of air pollutants concentrations due to air mass recirculation. In order to study the main factors governing the recirculation of an air mass under land-sea breeze conditions, a single station characterization of the recirculation potential in an airshed is implemented using a simplified land-sea breeze analytical model. The factors studied are latitude, ambient wind intensity, breeze intensity and friction. A sensitivity analysis performed reveals that the highest potential for coastal recirculation exists around latitude 30° with low friction values. It is found that the combined effect of latitude, breeze intensity and the meridional component of the ambient wind has the biggest influence on the model and is responsible for 31% of its variance. Also, latitude and breeze intensity account each for about 20% of the variance. The recirculation model is found to be highly sensitive to latitude, particularly in mid latitudes and to breeze intensity for weak breeze winds. The performance of the recirculation model is compared to 5-year measurements of recirculation at the East Mediterranean Sea during typical summer conditions. In spite of its rudimentary nature, the model does succeed in giving good quantitative measure of the recirculation, in the order of 0.3 on a scale of 0-1, very close to the observed values in the region.

Survival of plant pathogens under structural solarization

Structural solarization of greenhouses is a nonchemical sanitation procedure. The method involves dry heating, since maximal temperatures may exceed 60°C and consequent relative humidity (r.h.) is low (ca 15%), under fluctuating temperature and r.h. regimes. Thirty-five structural solarization experiments were performed over 7 years, testing one bacterial and five fungal plant pathogens. Various aspects of pathogen thermal inactivation under this method were studied. Thermal inactivation of the various pathogens differed according to the organism and inoculum form. Sensitivity to heat was highest withClavibacter michiganensis subsp.michiganensis and lowest withFusarium oxysporum f.sp.radicislycopersici inoculum in dry infected tomato stems, with ED80 values of 7 and 47 days, respectively; intermediate values were obtained forPythium sp.,F. oxysporum f.sp.melonis, F. oxysporum f.sp.basilici andSclerotium rolfsii. The maximal ambient temperatures were in the range of 28.2° to 33.1°C. Structural solarization for sanitation can be a useful component of integrated pest management in greenhouses.