SE—Structures and Environment

Optimized control strategies for carbon dioxide (CO2) enrichment of greenhouse tomato crops using CO2 from the exhaust gases of boilers burning natural gas are presented. In one group of strategies, the heat produced during CO2 generation which exceeds the immediate heat requirement of the greenhouse is stored as hot water and used subsequently for heating. The simulations show that, use of optimal control can increase the financial margin of crop value over the combined expenditure on gas used for CO2 and heating by £2.3 m-2 (11%) when heat is not stored and by £4.9 m-2 (24%) when heat is stored, compared with enriching with CO2 only when heating is required. A 30% increase in gas price reduced the financial margin by 11%, whereas a 30% increase in tomato price increased the margin by 40%. The capacity of the heat store places a limit on the amount of heat that can be stored and consequently on the amount of natural gas that can be burnt and the associated amount of CO2 produced during the day. The optimum size of heat store is 20 × 10-3 m3 per unit greenhouse area. © 2002 Silsoe Research Institute. Published by Elsevier Science Ltd. All rights reserved

SE—Structures and Environment

Two optimal control strategies for carbon dioxide (CO2) enrichment in greenhouse tomato crops have been developed. One uses pure CO2 from a storage tank and the other uses CO2 contained in the exhaust gases of boilers burning natural gas. The optimal strategies maximize the financial margin between crop value and the combined costs of the CO2 used for enrichment and the natural gas used for heating. In this paper, the strategy for optimal control using pure CO2 is presented and compared with strategies used by growers. The optimal strategy for enrichment with exhaust gas derived CO2 is presented in an accompanying paper. Simulations show that at a cost of £0.09 kg-1 for pure CO2 and £0.10 m-3 for natural gas, the optimal enrichment strategy would increase the annual margin of crop value over CO2 and heating costs by £4.6 m-2 (27%) compared to a basic control strategy of enrichment to a concentration of 1000 v.p.m. (parts per million by volume) when ventilators are < 5% open, otherwise enrichment to 350 v.p.m. The optimal CO2 concentration was expressed as an algebraic function of solar radiation, wind speed and ventilator opening angle, and so enabled a quasi-optimal value to be obtained using variables measured by greenhouse environmental controllers. The quasi-optimal equation, with coefficients averaged from simulations over 4 years, gave an increased margin over the basic control strategy of £4.4 m-2 (26%). © 2002 Silsoe Research Institute. Published by Elsevier Science Ltd. All rights reserved

Is the Recent Decrease in Airborne Ambrosia Pollen in the Milan Area Due to the Accidental Introduction of the Ragweed Leaf Beetle Ophraella Communa?

This study aims to determine whether a significant decrease in airborne concentrations of Ambrosia pollen witnessed in the north-west of the Province of Milan in Northern Italy could be explained by environmental factors such as meteorology, or whether there is evidence to support the hypothesis that the decrease was related to the presence of large numbers of the oligophagous Ophraella communa leaf beetles that are used as a biological control agent against Ambrosia in other parts of the world. Airborne concentrations of Ambrosia, Cannabaceae and Urticaceae pollen data (2000–2013) were examined for trends over time and correlated with meteorological data. The amount of Ambrosia pollen recorded annually during the main flowering period of Ambrosia (August–September) was entered into linear regression models with meteorological data in order to determine whether the amount of airborne Ambrosia pollen recorded in 2013 was lower than would normally be expected based on the prevailing weather conditions. There were a number of significant correlations between concentrations of airborne Ambrosia, Cannabaceae and Urticaceae pollen, as well as between airborne pollen concentrations and daily and monthly meteorological data. The linear regression models greatly overestimated the amount of airborne Ambrosia pollen in 2013. The results of the regression analysis support the hypothesis that the observed decrease in airborne Ambrosia pollen may indeed be related to the presence of large numbers of O. communa in the Milan area, as the drastic decrease in airborne Ambrosia pollen in 2013 cannot be explained by meteorology alone