Changing rice environment in the Philippines
2004
Centeno, H.G.S. | Pascual, Z.P. | Ferrer, A.B. | Sheehy, J.E.,International Rice Reseach Inst., Los Banos, Laguna (Philippines)
The net effects of climate change on rice yields are difficult to predict. Rising carbon dioxide levels in the atmosphere could lead to yield increases whereas atmospheric pollutants could cause yields to decline. Almost nothing is known about the concentration of ozone in the Philippines and in 2001, the authors began to monitor it in Los Banos using automated environmental monitoring system (EMS) that was installed at the IRRI. Samples of air were collected at 3 m height, 1.4 m height, and 0.1 m above the crop canopy. The samples were automatically pumped into the EMS and analyzed for SO2, NO, NOx and O3 concentrations. Hourly mean gas concentrations were recorded for 3 years (2001-2003) on a data logger. This study investigates diurnal and seasonal patterns on real-time concentrations of SO2, NO, NOx, and O3 collected at IRRI. The highest recorded ozone concentrations was 91.4 ppb at noon of 26 Aug 2002. The mean daily (24-hr) concentration of O3 was about 26 ppb. Studies in Europe have shown that such levels can reduce yields by about 20-40%. Ozone concentrations increase with high solar radiation (40 MJ/sq m) and daily maximum temperature (30 deg C). Ozone is produced in a series of reactions involving emissions from motor vehicles mainly in the form of nitrogen oxides. The ozone is related to nitrogen oxide concentration. The observed quantities of NOx in the air depend on motor vehicle emissions, moisture content, and wind direction. The SO2 levels are generally low (10 ppb). Tropospheric pollution appears to be closely linked with the local level of commuter activities.
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