Risk analysis by emission source strengths and wind directions of trace gases at Map Ta Phut Industrial Estate, Rayong province, Thailand

摘要

When air mass is flowing across the source area, it can lead to emissions and subsequently higher emissions of atmospheric concentrations of trace gases. It is well known that wind direction plays a significant role on atmospheric concentrations of persistent organic pollutants (POPs). While temperature and wind speed are obviously important parameters governing the atmospheric concentration of trace gases, these two parameters alone fail to entirely predict the atmospheric concentration of trace gases. Alternatively, wind direction may also be a controlling parameter for trace gas concentrations. Given that wind direction is measured as an angle (α) relative to true north (0), mean direction was determined by using trigonometric relations to determine the direction of the resultant of individual wind vectors. The emission source strength - wind direction relationship can be represented graphically by plotting R-value of (natural logarithm of partial pressure) vs against downwind angle (α) during the monitoring period. To apply this relationship, measured atmospheric concentrations must be expressed as partial pressures (P), which can be converted through the use of the ideal gas law with a temperature correction. The aims of this study are to statistically quantify the relationships between emission source strengths and downwind angles of sulphur dioxide, nitric oxide, nitrogen dioxide and ozone measured at five monitoring stations adjacent to Map Ta Phut Industrial Estate during 28/08/08 - 23/07/09. R-values of gaseous SO_2, NO, NO_2, NO_x and O_3 measured at POS and ITS tended to be higher than those of trace gases detected at other sites. Significant positive correlations (p < 0.05) were found in downwind angles ranging from 180° to 240° for SO_2 monitored at POS and ITS, suggesting the proper selection of these observatory sites as a part of risk analysis in a residential zone. In addition, the probability distribution analysis revealed that the emission source strengths of SO_2 in POS and ITS have relatively low fluctuations comparing with those of other observatory sites.