Experimental assessment of tropical surface ozone related to land utilization in Central Thailand

Abstract

Surface ozone (O 3 ) is a harmful air pollutant that is created through complex atmospheric photochemical reactions between nitrogen oxides (NO x ) and various precursors. Its abundance depends on the associated chemical pathways, local environmental conditions, and meteorological factors, the latter of which affects the dispersal of O 3 . This research investigates vertical and horizontal variations in NO 2 and O 3 in urban and rural areas associated with atmospheric parameters at 13 monitoring locations stretching from greater Bangkok to Ratchaburi Province, Thailand. O 3 and NO 2 were measured concurrently with temperature and relative humidity using calibrated portable devices (Aeroqual, Series 500), typically at heights of 1.5, 75, and 110 m. The instruments were mounted on a drone to obtain measurements at elevations of 75 m and 110 m. The data obtained showed that even in the lowest part of the boundary layer, the average concentrations of O 3 in the urban area increased by nearly 21% with altitude from the ground (26.8 ± 4.7 ppb at 1.5 m) to 110 m. However, in the rural area, the average ground concentrations of O 3 were higher (38.6 ± 11.8 ppb) but they decreased by approximately 43% at 110 m. Notably, at all monitoring sites, NO 2 concentrations exhibited a decreasing trend with height above the ground. As the wind conditions were stagnant, the ground measurements at each station were representative of local conditions. However, modelling of air mass backward trajectories indicated that despite the stagnant conditions at the ground level, there were contributions from long-range transport (even within the shallow atmospheric layers) at elevations as low as 110 m above the ground.