Diurnal and seasonal variations in the carbon dioxide concentration of the lower atmosphere in the coastal plain of Israel

Abstract

Bulk-air carbon dioxide concentration at 5 m was recorded each week for 24 h, from October 1973 to September 1974. Measurements were made at a site typical of the agricultural environment in the Central Coastal Plain of Israel. CO 2 concentrations fluctuated from minute to minute; amplitudes were up to 100 vpm within 1 h during calm nights and 10 vpm during midday hours. Summarized data giving maximal and minimal values within each hour and the mean CO 2 concentration on the hour are presented. Most of the daylight (09–17 h) values ranged between 330 and 335 vpm throughout the year, though during October 1973 mean values of 354 were reached. Nocturnal CO 2 build-up reaching mean values of 373 around 04 h resulted in a diurnal yearly mean of 349 vpm, about 25 vpm above the global mean CO 2 concentration. The diurnal mean for each month was within ± 10 vpm of the yearly mean for 9 months of the year. The month to month variation was largely caused by differences in nocturnal CO 2 concentrations. It is argued that the elevated CO 2 concentrations at night increased near-ground temperatures by up to 0.5°C. Calculation of net photosynthesis in a C 3 plant in Israel indicated that the global CO 2 concentration increase (from 300 to 330 vpm), that has taken place in this century, has increased mean yearly photosynthesis by 3.1% and that the higher CO 2 concentrations found at the sampling site added another 0.4%.