Exposure-plant response of ambient ozone over the tropical Indian region

A high resolution regional chemistry-transport model has been used to study the distribution of exposureplant response index (AOT40, Accumulated exposure Over a Threshold of 40 ppb, expressed as ppb h) over the Indian geographical region for the year 2003 as case study. The directives on ozone pollution in ambient air provided by United Nations Economic Commission for Europe (UNECE) and World Health Organization (WHO) for vegetation protection (AOT40) have been used to assess the air quality. A substantial temporal and spatial variation in AOT40 values has been observed across the Indian region. Large areas of India show ozone values above the AOT40 threshold limit (3000 ppb h for 3 months). Simulated AOT40 values are found to be substantially higher throughout the year over the most fertile Indo-Gangetic plains than the other regions of India, which can have an adverse effect on plants and vegetation in this region. The observed monthly AOT40 values reported from an Indian station, agree reasonably well with model simulated results. There is an underestimation of AOT40 in the model results during the periods of highest ozone concentration from December to March. We find that the simulated AOT40 target values for protection of vegetation is exceeded even in individual months, especially during November to April. Necessary and effective emission reduction strategies are therefore required to be developed in order to curb the surface level ozone pollution to protect the vegetation from further damage in India whose economy is highly dependent on agricultural sector and may influence the global balance

Threshold exceedances and cumulative ozone exposure indices at tropical suburban site

This 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

Tropospheric ozone (TOR) trend over three major inland Indian cities: Delhi, Hyderabad and Bangalore

An analysis of tropospheric column ozone using the NASA Langley TOR data during 1979-2005 has been done to investigate the trend over major Indian cities Delhi, Hyderabad and Bangalore. India was under social democratic-based policies before 1990s. Economic Liberalization began in nineties which lead to a significant growth in industrial, energy and transport sectors in major cities. Our analysis shows that there is a systematic increase in the number of months with higher tropospheric ozone values after 1990. A comparison of TOR climatology before and after 1990 over these cities shows evidence of increase in the tropospheric ozone after 1990. Trend obtained from the model shows significant change during monsoon over Delhi and during pre-monsoon and post-monsoon over Hyderabad and Bangalore. The present analysis using TOR technique demonstrates the TOR potential to detect changes in tropospheric ozone over large cities which are impacted by large anthropogenic pollution

Temporal evolution of measured climate forcing agents at South Pole, Antarctica

Greenhouse gas (GHG; mainly CO 2, CH 4, N 2O, CFC-11 and CFC-12) measurements for 22 years (1983-2004) have been analysed to evaluate the radiative forcing (RF) and temporal evolution at the South Pole. About 20 increase in growth rate of CO 2 has been observed during 1992-2004 compared to 1983-91. However, remarkable deceleration in the growth rate of CH 4, CFC-11 and CFC-12 has been observed. CO 2 radiative forcing has increased by ~49 during 2004 for 10 increase in CO 2 concentration during the last 22 years. RF due to CH 4 was found to be 0.47 Wm -2 in 1999 and since then has remained almost constant through 2004. The net RF has been observed to increase by 0.7 Wm -2 during 2004 compared to 1983, which corresponds to ~38 increase in the last 22 years. Growth rate of net RF decreased by ~22 during 1990-2004, compared to the growth rate during 1983-90. A global warming simulation made using the EdGCM model shows an increase in surface air temperature and sea surface temperature of about 1.7 oC and 1 oC respectively, in 2050 compared to 1958. In response to change in GHGs from 1958 to 2050, warming over the higher latitudes is greater than in the tropics and also increase in minimum temperature is greater than the increase in maximum temperature. Similarly, up to 50 change in snow-ice cover over some of the regions in the higher latitudes is observed with this simulation

Impact of emission mitigation on ozone-induced wheat and rice damage in India

In this study, we evaluate the potential impact of ground level ozone (O3) on rice and wheat yield in top 10 states in India during 2005. This study is based on simulated hourly O3 concentration from the Weather Research and Forecasting model coupled with Chemistry (WRF-Chem), district-wise seasonal crop production datasets and accumulated daytime hourly O3 concentration over a threshold of 40 ppbv (AOT40) indices to estimate crop yield damage resulting from ambient O3 exposure. The response of nitrogen oxides (NOx) and volatile organic compounds (VOC) mitigation action is evaluated based on ground level O3 simulations with individual reduction in anthropogenic NOx and VOC emissions over the Indian domain. The total loss of wheat and rice from top 10 producing states in India is estimated to be 2.2 million tonnes (3.3%) and 2.05 million tonnes (2.5%) respectively. Sensitivity model study reveals relatively 93% decrease in O3-induced crop yield losses in response to anthropogenic NOx emission mitigation. The response of VOC mitigation action results in relatively small changes of about 24% decrease in O3-induced crop yield losses, suggesting NOx as a key pollutant for mitigation. VOC also contribute to crop yield reduction but their effects are a distant second compared to NOx effects

Air pollution, air quality, and climate change

The introduction of gases and particulate contaminants in the atmosphere due to natural or human activities causes air pollution. The concentration and toxicity of these contaminants define air quality and in the long term contribute to climate change. Both air pollution and climate change influence each other through complex interactions in the atmosphere. This issue has 9 very interesting manuscripts, touching various aspects of air pollution and air quality and their impact on climate chang

Air Pollution, Air Quality and Climate Change (Editorial)

The introduction of gases and particulate contaminants in the atmosphere due to natural or human activities causes air pollution. The concentration and toxicity of these contaminants define air quality and in the long term contribute to climate change. Both air pollution and climate change influence each other through complex interactions in the atmosphere. This issue has 9 very interesting manuscripts, touching various aspects of air pollution and air quality and their impact on climate change

Radiative forcing of black carbon over Delhi

The radiative effects of black carbon (BC) aerosols over New Delhi, the capital city of India, for the period August 2010–July 2011, have been investigated using Santa Barbara DISTORT Atmospheric Radiative Transfer (SBDART) model in the present paper. The monthly mean BC concentrations in Delhi, an urban location, vary in between 15.935 ± 2.06 μg m−3 (December 2010)–2.44 ± 0.58 μg m−3 (July 2011). The highest value for monthly mean BC forcing has been found to be in November 2010 (66.10 ± 6.86 Wm−2) and the lowest in July 2011 (23 ± 3.89 Wm−2). Being the host city for the XIX Commonwealth Games (CWG-2010), government of Delhi set up a plan to reduce emissions of air pollutants during Games, from 03 October to 14 October, 2010. But opposite to the expectations, the emission controls implemented were not sufficient to reduce the pollutants like black carbon (BC), and therefore relatively a high value of BC radiative forcing (44.36 ± 2.4) was observed during the month of October 201

Ozone in ambient air at a tropical megacity, Delhi: Characteristics, trends and cumulative ozone exposure indices

Seven year data of hourly surface ozone concentration is analyzed to study diurnal cycle, trends, excess of ozone levels above threshold value and cumulative ozone exposure indices at a tropical megacity, Delhi. The ozone levels clearly exhibit a diurnal cycle, similar to what has been found in other urban places. A sharp increase in the ozone levels during forenoon and a sharp decrease in the early afternoon can be observed. The average rate of increase in ozone concentration between 09 and 12 h has been observed to be 7.1 ppb h -1. We find that the daily maximum and daytime 8-h (10-17 h) ozone levels are increasing at a rate of about 1.7 (± 0.7) and 1.3 (± 0.56) ppb y-1, respectively. The directives on ozone pollution in ambient air provided by United Nations Economic Commission for Europe and World Health Organization for vegetation (AOT40) and human health protection were used to assess the air quality. The present surface ozone levels in the city are high enough to exceed "Critical Levels" which are considered to be safe for human health, vegetation and forest. The human health threshold was exceeded for up to ~45 days per year. The AOT40 (Accumulated exposure Over a Threshold of 40 ppb) threshold was exceeded significantly during winter (D-J-F) and pre-monsoon (M-A-M) (Rabi crop growing season) season in India. Translating AOT40 exceedances during pre-monsoon into relative yield loss we estimate yield loss of 22.7, 22.5, 16.3 and 5.5 for wheat, cotton, soybean and rice, respectively. © 2009 Springer Science+Business Media B.V

Enhancements in nocturnal surface ozone at urban sites in the UK

Analysis of diurnal patterns of surface ozone (O3) at multiple urban sites in the UK shows the occurrence of prominent nocturnal enhancements during the winter months (November–March). Whilst nocturnal surface ozone (NSO) enhancement events have been observed at other locations, this is the first time that such features have been demonstrated to occur in the UK and the second location globally. The observed NSO enhancement events in the UK were found to be so prevalent that they are clearly discernible in monthly diurnal cycles averaged over several years of data. Long-term (2000–2010) analysis of hourly surface ozone data from 18 urban background stations shows a bimodal diurnal variation during the winter months with a secondary nighttime peak around 0300 hours along with the primary daytime peak. For all but one site, the daily maxima NSO concentrations during the winter months exceeded 60 μg/m3 on >20 % of the nights. The highest NSO value recorded was 118 μg/m3. During the months of November, December, and January, the monthly averaged O3 concentrations observed at night (0300 h) even exceeded those observed in the daytime (1300 h). The analysis also shows that these NSO enhancements can last for several hours and were regional in scale, extending across several stations simultaneously. Interestingly, the urban sites in the north of the UK exhibited higher NSO than the sites in the south of the UK, despite their daily maxima being similar. In part, this seems to be related to the sites in the north typically having lower concentrations of nitrogen oxides