Sachin D. Ghude

Observational study of surface ozone at New Delhi, India

Surface ozone has been measured over New Delhi, an urban site, a region of intensive anthropogenic activity since 1997. Seasonal variations in ozone concentration show pronounced maxima in the summer and autumn seasons and minima in monsoon and winter seasons. Diurnal patterns in ozone concentration show daytime in situ photochemical production throughout the year. The high ozone episode days were associated with meteorological parameters such as sunny and warm weather, stagnant wind patterns and low relative humidity. The monthly average maximum concentration in summer was found to be in the range of 62–95u2009ppb whereas, it was found to be 50–82u2009ppb in the autumn (October and November). The analysis of hourly averaged surface ozone data illustrates that on a large number of days the surface ozone values at Delhi exceed the World Health Organization (WHO) ambient air quality standards (hourly average of 80u2009ppb) for ozone. On some occasions, night‐time increases of surface ozone concentration have been observed under stable boundary layer conditions and during thunderstorms.

Threshold exceedances and cumulative ozone exposure indices at tropical suburban site

[1]xa0This study provides the first analysis of threshold exceedances and cumulative ozone exposure indices from Pune, a tropical suburban site in India. We used the directives on ozone pollution in ambient air provided by the United Nations Economic Commission for Europe, and by the World Health Organization to assess the air quality from in situ measurements of surface ozone (during the years 2003–2006). We find that the exposure-plant response index (Accumulated exposure Over a Threshold of 40 ppb (AOT40)) and target values for protection of human health (8-h > 60 ppb) are regularly surpassed. This is a concern for agricultural and human health. Air-mass classification based on back-air trajectories shows that the excess of AOT40 values is quite plausibly due to long-range transport of background ozone and its precursors to the measurement site.

Regional CO pollution over the Indian-subcontinent and various transport pathways as observed by MOPITT

We used day-side Measurement of Pollution in the Troposphere (MOPITT) carbon monoxide (CO) retrievals (2000–2007) to examine the regional CO emission and its transport pathways during the summer/winter monsoon, with a specific focus on the Indian-subcontinent. It is observed that MOPITT CO retrievals at 850 hPa level in general show large scale features of CO emission in India, as reflected in the bottom-up inventory. In particular, high CO mixing ratios over the eastern north-eastern part of India, along the Indo-Gangetic (IG) region, and low CO mixing ratios over central India are generally captured from the MOPITT data. A strong plume with enhanced CO mixing ratios at 350u2009hPa is observed during the summer monsoon, demonstrating large scale vertical transport of the boundary layer CO from the Indian region into the upper troposphere. During winter outflow CO from the Indian region is found to be transported over the Arabian Sea and Bay of Bengal and reaches up to Saudi Arabia and north-eastern Africa. It is observed that emissions from Southeast Asia and the eastern north-eastern Indian region have the greatest impact over the Bay of Bengal and the eastern Indian Ocean, while emissions from the rest of India dominate over the Arabian Sea and the western Indian Ocean.

Tropospheric ozone variability over the Indian coastline and adjacent land and sea

A tropospheric ozone variability study is carried out to investigate the spatial and temporal distribution over the coastline of the Indian peninsula and adjacent land and sea using NASA Langley Tropospheric Ozone Residual data set for the period 1979–2005. A strong seasonal cycle has been observed with large variation (∼ 55%) over the upper eastern coast, followed by the upper and lower western coast, compared to the lower eastern coast (∼ 33%). A negative gradient in ozone concentration is observed along eastern and western coasts during summer (slope ∼ –0.78 and –0.65) and a positive gradient (slope ∼ 0.16 and 0.21) during winter. The same is observed over the adjacent land and sea along the coastline with slight variation. This change in gradient can be attributed to the anthropogenic emission of precursor gases that reinforce localized photochemical production of ozone. In addition, topography, transport, seasonality of emission of precursor gases and the solar insolation cycle play a vital role.

Evidence of seasonal enhancement of CO in the upper troposphere over India

The vertical profiles of carbon monoxide (CO) mixing ratios retrieved from the Earth Observing System (EOS), Microwave Limb Sounder (MLS) onboard the Aura satellite for the period 2005–2009 and the EOS Tropospheric Emission Spectrometer (TES) onboard Aura for the period 2006–2007 were used to examine the evolution of pollutant CO in the upper troposphere (UT) over India. The Model for OZone And Related chemical Tracers version 2 (MOZART-2) was used to examine the seasonal transport of CO in the UT. The satellite observations revealed vertical transport of CO (80–90 ppb) from the surface to the UT during the summer monsoon season. The regular feature of enhancement of CO in the UT over India is presented. The results obtained by the MOZART-2 simulations (for the years 2000–2005) agree with the observations and indicate transport of boundary layer CO to the tropopause during the monsoon season. The observed enhanced CO mixing ratios in the UT are explained by processes involving monsoon convection.

Comparative study of the total ozone column over Maitri, Antarctica during 1997, 2002 and 2003

The total ozone (TOZ) column was measured using a Microtop Sun‐photometer at Maitri (70° 45′u2009S, 11° 44′u2009E), Antarctica during the 16th, 21st and 22nd Indian Scientific Expedition to Antarctic. A comparative study of the TOZ column at Maitri, Antarctica was made to understand the behaviour of the ozone hole. The observations showed a direct relationship between the stratospheric temperature anomaly and year‐to‐year variation in TOZ. The minimum TOZ observed at Maitri, Antarctica during spring was 135u2009DU (Dobson unit), 185u2009DU and 126u2009DU in 1997, 2002 and 2003, respectively. The ozone hole in 2003 was much deeper and had a longer duration. The observations showed that chemical loss of ozone over Maitri during the ozone hole period in 2003 was increased by 18.6% when compared with 1997 and 42% when compared with 2002. The observations at Maitri also showed an event of major stratospheric warming along with surface warming during 2002. A temporary sudden rise in the TOZ column before the recovery period (days 300–315) was also observed and found to be overlapping in all the observational years.