Seasonal and Diurnal Concentrations of Ambient Formaldehyde and Acetaldehyde in Bangkok

The concentration level of carbonyl compounds in Bangkok ambient air were measured in five roadside sites and five residential sites during July 2007 to April 2008. About 250 samples were collected and ten carbonyls were identified. Formaldehyde and acetaldehyde were the most abundant carbonyl compounds found in Bangkok ambient air. The ambient concentration of formaldehyde at the roadside areas in Bangkok during July 2007 to April 2008 ranged from 5.14 to 17.2 ??g/m³ (average 11.53 ??g/m³) while, the ambient concentrations of formaldehyde in residential areas in Bangkok during the same period ranged from 3.06 to 19.9 ??g/m³ (average 9.65 ??g/m³). The concentrations of acetaldehyde in roadside areas ranged from 1.59 to 7.95 ??g/m³ (average 3.51 ??g/m³) while at the residential areas the concentrations of acetaldehyde during the same period ranged from 1.07 to 8.05 ??g/m³ (average 3.11 ??g/m³). Other compounds showed low concentration. The concentrations of formaldehyde and acetaldehyde were low during the rainy season due to rain washout since these compounds are water soluble. The concentrations were high during the cold season due to stable conditions during these months. The concentrations slightly decreased during the summer due to photochemical reactions and photolysis under extreme temperature. Formaldehyde and acetaldehyde showed good correlation during 17:00 P.M. to 05:00 A.M. due to absence of solar radiation that may enhance photochemical reactions and mobile sources may be the sources of emission in the environment. It was also found that the concentrations of formaldehyde and acetaldehyde were low during the night time.     

Effects of Photosynthetically Active Radiation and Air Temperature on CO2 Uptake of Pterocarpus macrocarpus in the Open Field

Since trees and plants can absorb CO2, forests are widely regarded as a carbon sink that may control the amount of CO2 in the atmosphere. The CO2 uptake rate of plants is affected by the plant species and environmental conditions such as photosynthetically active radiation (PAR), temperature, water and nutrient contents. PAR is the most immediate environmental control on photosynthesis while air temperature affects both photorespiration and dark respiration. In the natural condition, PAR and temperature play an important role in net CO2 uptake. The effects of PAR and air temperature on the CO2 uptake of Pterocarpus macrocarpus grown in a natural habitat were studied in the present work. Due to many uncontrollable factors, a simple rectangular hyperbola could not represent the measured data. The data were divided into groups of 2℃ intervals; CO2 uptake in each group may then be related to PAR by a rectangular hyperbola function. Using the obtained functions, the effect of PAR was removed from the original data. The PAR-independent CO2 uptake was then related to air temperature. Finally, the effects of PAR (I) and air temperature (Ta) on the CO2 uptake rate (A) were combined as:A= [(-0.0575 Ta2+ 2.6691 Ta-23.264)I/(-4.8794Ta2+227.13Ta-2456.9)+I](-0.00766Ta2+0.40666Ta-3.99924)