Ozone, a very reactive gas is found in very small quantities in the atmosphere. Its mean concentration can vary from a few to hundreds of parts per billion (ppb) depending on the location and altitude. At the surface layer, ozone is considered a secondary pollutant which causes oxidant episodes such as haze and smog. In the stratosphere, the layer of ozone reduces harmful ultraviolet radiation reaching the earth's surface. On a global scale,  ozone is a greenhouse gas which contributes to global warming.

Globally, due to rapid development, ozone concentrations throughout the vertical atmosphere is affected. Surface ozone levels are increasing while ozone in the stratosphere is being depleted. To monitor and assess these changes, the Malaysian Meteorological Department (MMD) began ozone monitoring in 1992 at the MMD headquarters in Petaling Jaya. The ozone monitoring programme of MMD includes monitoring of vertical ozone profile and total column ozone in the atmosphere.

Vertical Ozone Profile

The vertical ozone profile is measured by releasing an ozonesonde attached to a balloon into the upper atmosphere. Signals transmitted from the ozonesonde are received by a ground station. The monthly soundings obtained showed that ozone concentrations peak sharply in the stratosphere at a height of about 25 kilometers.

Total Column Ozone

Total column ozone observations are made with a Brewer Ozone Spectrophotometer which measures the relative intensities of selected pairs of ultraviolet wavelengths of light emanating from the sun and zenith sky to determine the amount of ozone in the atmospheric column. Total ozone values measured during the year 2009 varied from 231 to 270  Dobson units.

For more information, see Atmospheric Ozone.