Effects of Temperature, Relative Humidity and Traffic Density on the Concentration of Acid Substances in the Congested Area

Abstract

The concentrations of acid substances in the atmosphere in the forms of both acidic gases andaerosols were monitored at The Phloen Chit sky train station in downtown Bangkok for 5 months fromNovember 2006 to March 2007. The air samples were collected by a four - stages filter packs. The trafficdensity around the monitoring area was 140,000 vehicles/day. The results of this study showed that theaverage concentrations of aerosols in the forms of anion and cation components were found to be 78, 67,and 73, 67 nmol/m3 for SO₄^-2, NO^3- and Ca²⁺, NH⁴⁺, respectively. The gaseous concentrations in theatmosphere were 835, 162, 45 and 39 nmol/m³ for NH₃, SO₂, HCl and HNO₃, respectively. Regarding tothe effects of the temperature, the concentration of both acidic gases and aerosols varied directly with thetemperature, except for NH₃. For the relative humidity, it showed no effect on the amount of the acidicgases or aerosol formations, except for SO₂ in which it was inversely varied with the relative humidity.Further study on the influence of the traffic density, the result showed no distinctive relationship betweenthe concentration of the gases and aerosols and the variation in the traffic density.

Keywords : Urban Area / Acid Concentration / Temperature / Relative Humidity / Traffic Density