Observations of NO2 at the Manila Observatory in the Ateneo de Manila Campus (Quezon City, Philippines) are analyzed. These have been made with a Differential Optical Absorption Spectroscope (DOAS) during the two months of June and August 2002.
The concentrations have been analyzed in order to determine
the characteristics of the time variations. The analysis shows that the average concentration in August is greater than that of June. On the basis of all of the observations, the average variation during a 24-hour period is semi-diurnal. The maximum concentrations occur in the morning as well as in the evening. The evening maximum is higher than the morning maximum. An examination of the day-to-day variations indicates the occurrence of four types of diurnal variations with the following characteristics: Type 1: Major maximum in the evening and a minor or negligible morning maximum; Type 2: Only one maximum which occurs near noontime; Type 3: Major morning maximum and insignificant or minor evening maximum; Type 4: Low concentrations without any significant maximum or minimum throughout the 24-hour period.
These variations may be explained basically by corresponding variations in the large scale prevailing atmospheric conditions. These conditions control the development of different types of mesoscale disturbances. These different types of mesoscale disturbances, in turn, result in the occurrences of different types of diurnal variations in the concentrations.