NATIONAL AGENCY FOR METEOROLOGY AND ENVIRONMENTAL MONITORING, MONGOLIA 48 INFLUENCE OF PHOTOCHEMISTRY AND METEOrOLOgy ON SEASONAL VAriATiON OF SURFACE OZONE Sandelger Dorligjav 1 , Erdenesukh Sumiya 1 , Gomboluudev Purevjav 2 1 School of Arts and Sciences, National University of Mongolia 2 Sector of Climate Research, Information and Research Institute of Meteorology, Hydrology and Environment Abstract In this study, the temporal variability of surface ozone along with a study of the effects of the photochemistry and meteorological processes on the surface ozone concentrations over Ulaanbaatar city is investigated using the surface observation, radiosonde, reanalysis and back trajectory of air mass data during 2014. Keywords: an ozone precursor, temperature inversion, the wind, stratospheric intrusion Introduction Although, near-surface ozone (O 3 ) is a local and regional pollutant with adverse effects on the human health and vegetation (e.g., WHO, 2000), it is responsible for the production of the highly reactive hydroxyl radical (OH), which oxidizes and removes the majority of pollutants from the atmosphere (e.g., Levy, 1971). The amount of the surface ozone at any location depends upon the amount of its supply from the stratosphere (e.g., Junge, 1962), rate of photochemical production of some pollutants such as carbon monoxide (CO), methane (CH 4 ), and other non-methane compounds (e.g., Crutzen, 1995), transport from other regions (e.g., Dop, 1977; Lal et al., 2013), and the rate of its destruction on the earth’s surface either due to dry deposition (e.g., Park et al, 2014) or photochemical loss mechanisms (e.g., Monks, 2005; Ganguly, 2012). Trainer et al., (2000) summarized this that the time derivative of the ozone is the result of the chemical and dynamical processes that effect on the ozone mixing ratio (Eq. 1). (Eq.1) Where: - represents the sum of the horizontal and vertical transport (stratospheric intrusion), - represents the net ozone production, including