Seasonal progression of surface ozone and NOx concentrations over three tropical stations in North-East India

Monitoring of surface ozone (O₃) and Nitrogen Oxides (NOx) are vital for understanding the variation and exposure impact of these trace gases over the habitat. The present study analyses the in situ observations of surface O₃ and NOx for January-December 2016, for the first time over three sites of North-Eastern India (Aizwal, Gauhati and Tezpur). The sites are major cities of north-eastern India, located in the foothills of Eastern Himalaya and have no industrial impacts. We have analysed the seasonal variation of O₃ and NOx and found that the site Tezpur, which is in the valley area of Eastern Himalaya, is experiencing higher values of pollutants persisting for a long time compared to the other two stations. The correlation of surface O₃ with the air temperature at all three sites suggested that all the O₃ may not be locally produced, but has the contribution of transported pollution reaching to stations. The study also attempts to discover the existing variability in the surface O₃ and NOx over the study area by employing continuous wavelet analysis.

Interdecadal Variations of the Midlatitude Ozone Valleys in Summer

Using the ERA-Interim total column ozone data, the spatial distributions of the long-term mean of the global total ozone in summer are analyzed. The results demonstrate that there are three midlatitude ozone “valleys” on earth—they are centered over the Tibetan Plateau (TIP), the Rocky Mountains (ROM), and the Southwest Pacific (SWP), respectively. The interdecadal variations of the three ozone valleys are positively modulated by the solar radiation, and the TIP ozone’s correlation with the solar radiation gets maximized with a two-year lag. The interdecadal variation of the SWP ozone valley has a significantly negative relationship with the Pacific Decadal Oscillation (PDO) and the South Pacific quadrupole (SPQ). Warm sea surface temperature anomalies (SSTAs) associated with the SPQ strengthen the vertical ascending motion, which dilutes the high concentration ozone at high altitudes. The interdecadal variation of the ROM ozone valley is positively correlated with the PDO, leading by three years. The ROM ozone content is also modulated by SSTAs in the Indian Ocean basin (IOB) by the circumglobal teleconnection (CGT). The observed regional SSTAs can exert a significant impact on the regional and even global circulation, via which the ozone content in midlatitudes also varies.

Does cosmic-ray-induced heterogeneous chemistry influence stratospheric polar ozone loss?

Cosmic-ray (CR) -induced heterogeneous reactions of halogenated species have been suggested to play the dominant role in causing the Antarctic ozone hole. However, measurements of total ozone in Antarctica do not show a compact and significant correlation with CR activity. Further, a substantial CR-induced heterogeneous loss of chlorofluorocarbons is incompatible with multiyear satellite observations of N2O and CFC-12. Thus, CR-induced heterogeneous reactions cannot be considered as an alternative mechanism causing the Antarctic ozone hole.