The variability of total column ozone (TCO) and tropospheric column ozone (TrCO) was examined in Central Asia. Measurements were conducted at the Lidar Station Teplokluchenka in eastern Kyrgyzstan for one year, July 2008–July 2009. TCO was obtained using a handheld Microtops II Ozonometer (TCO-MII) and from the Aura OMI (TCO-OMI) satellite. Nitrogen dioxide (NO2) and formaldehyde concentrations also were obtained from the OMI satellite. Formaldehyde was used as a surrogate for volatile organic compounds. TrCO was estimated by the difference between TCO-OMI and stratospheric column ozone retrieved from the MLS satellite. Comparison of the ground-based TCO-MII with TCO-OMI showed good agreement (r2 = 0.93), and linear regression between these was used to estimate missing values in the TCO-MII dataset.
The contribution of TrCO to TCO varied from 15% in summertime to 5% in winter. High values of TrCO were observed during summer (July: 45 DU) and low values during winter (December: 15 DU), as is typically observed. The average values of TrCO for summer, autumn, winter, and spring were equal to 42, 27, 20, and 30 DU, respectively. Seasonal variability of TrCO corresponded to solar intensity, indicating that TrCO is likely to form through photochemical means rather than stratospheric intrusion.
The spatial distribution of NO2 and VOC were examined to better understand the regional sources of these ozone precursors. Transport from highly populated areas of the Ferghana Valley and Tashkent in Uzbekistan contributed to the TrCO concentrations observed in this work. The HCHO/NO2 ratio, an indicator of the ozone production rate, suggested that reducing NO2 would be more effective in reducing TrCO during most of the year, except summer, when reductions of both would likely be needed.