Characteristics of the Ozone pollution and its Health Effects in India

Outdoor air pollution is a major environmental health problem. Exposure to air pollution leads to increased risk of respiratory diseases like acute respiratory infections and chronic obstructive pulmonary diseases; and cardiovascular diseases, such as stroke and ischemic heart disease. According to World Health Organization, one in eight total global deaths occurs as a result of exposure to air pollution.1 Over 3.5 million people die each year from outdoor air pollution. Lowand middle-income countries, especially the Western Pacific and South-East Asian countries account for about 88% of those premature deaths.1 According to a recent study by the Organization for Economic Co-Operation and Development (OECD), in India, the cost of air pollution to society in 2010 was estimated at US$ 0.5 trillion.2 Ozone is one of the air pollutants of major concern globally. Higher levels of ozone in the air can affect human health, leading to breathing problems, asthma exacerbation and reduced lung function. Several studies have also shown that daily mortality and heart diseases increase with exposure to high levels of ozone. MATERIALS AND METHODS


INTRODUCTION
Outdoor air pollution is a major environmental health problem.Exposure to air pollution leads to increased risk of respiratory diseases like acute respiratory infections and chronic obstructive pulmonary diseases; and cardiovascular diseases, such as stroke and ischemic heart disease.According to World Health Organization, one in eight total global deaths occurs as a result of exposure to air pollution. 1Over 3.5 million people die each year from outdoor air pollution.Low-and middle-income countries, especially the Western Pacific and South-East Asian countries account for about 88% of those premature deaths. 1 According to a recent study by the Organization for Economic Co-Operation and Development (OECD), in India, the cost of air pollution to society in 2010 was estimated at US$ 0.5 trillion. 2Ozone is one of the air pollutants of major concern globally.Higher levels of ozone in the air can affect human health, leading to breathing problems, asthma exacerbation and reduced lung function.Several studies have also shown that daily mortality and heart diseases increase with exposure to high levels of ozone.

MATERIALS AND METHODS
Literature search was carried out in PubMed, WHO website and Google Scholar.Inclusion criteria used were: articles published from 1980 to 2014 concerning ozone and its health effects with special reference to India, in any language and of any design.Articles on ozone layer and ozone depletion were excluded.Cross-references of articles included in the review were also searched.Key words used during the search were surface ozone, health effects, air pollution, mortality, morbidity, seasonal variations and ozone standards.All relevant articles were critically analysed and the contents were extracted into broad thematic areas for further interpretation.

RESULTS AND DISCUSSION
During the search a total of 55 relevant articles were identified and analysed.The results are presented below in the pre-identified thematic areas.transport of ozone and its precursors.Precipitation decreases the ozone concentration by means of wet deposition.Relative humidity chemically controls the ozone concentration and diurnal meteorological variations cause diurnal variation of ozone concentrations.

Ozone Guidelines
In 1997, the United States Environmental Protection Agency (EPA) proposed adding an ozone standard of 80 ppb based on the daily 8-hour maximum concentration.WHO Air Quality Guidelines for Europe (WHO AQG, 2000) had set the guideline value for ozone levels at 120 µg/m 3 for an 8-hour daily average.But studies have shown health effects at concentrations below 120 µg/m 3 .So WHO Air Quality Guidelines AQG in 2005 reduced the cut-off from 120 µg/m 3 to 100 µg/m3 (daily maximum 8-hour mean). 5In the year 2009, for the first time, India included ozone under its Revised National Ambient Air Quality Standards (NAAQS). 6According to this, the mean concentration of ozone in ambient air must be less than 100 µg/m 3 for any 8 hour period of monitoring and less than 180 µg/m 3 in hourly monitoring.This should be complied with 98% of the time in a year and in 2% of the time, they may exceed the limits but not on two consecutive days of monitoring. 7

Variations in Ozone level
The ground level ozone levels are not constant.It varies from country to country and even within a country varies from region to region.Monthly measurements at 50 stations in Asia, Africa, South America, and Europe showed that the median ozone concentrations were maximum at Waliguan Mountain, China (45ppb) and minimum at Petit Saut, French Guiana (8ppb).The highest ozone values were found in the mid-latitudes, with Northern hemisphere values exceeding the Southern hemisphere levels, and the lowest values found in the tropical regions. 8In India, in addition to regional variation, ozone shows diurnal (or daily) and seasonal variations as shown in Table 1.The ground-level ozone is maximum during summer and minimum during monsoon seasons.In naturally in the upper atmosphere (the stratosphere), 6 to 30 miles above the Earth's surface.This protective ozone layer shields the Earth from the sun's ultraviolet rays.But manmade chemicals are gradually destroying this layer, resulting in a "hole in the ozone" over the north and south poles.The tropospheric or ground level ozone lies in the Earth's lower atmosphere is an important photochemical pollutant.This surface ozone (O 3 ) is formed when pollutants like as Volatile Organic Compounds (VOCs) and oxides of nitrogen chemically react in the presence of sunlight.As a result, the highest levels of ozone pollution occur during periods of sunny weather.Cars, power plants, industrial boilers, refineries, chemical plants, and other sources emit these pollutants.Once formed, ozone is scavenged by NO and a "photo stationary state" is formed where concentrations of NO, NO 2 and O 3 are all inter-related.But the presence of CO and VOCs can disturb this steady state relationship by producing peroxy radicals and resulting in an increased ozone concentration. 3ue to the worldwide increase in the burning of fossil fuels, atmospheric CO 2 concentrations are currently rising at approximately 0.5% per year and surface ozone values are increasing at a rate of 0.32% per year. 4zone can be transported over long distances by wind and due to this even rural areas can experience high ozone levels.High ozone concentrations have also been observed in cold months, with high levels of local VOC and NO emissions.Smog is primarily made up of ground level ozone combined with other gases and particle pollution.Surface ozone is also a greenhouse gas which contributes to climate change.

Factors influencing ozone concentration
Many meteorological factors influence ozone concentration.Solar irradiation and temperature influence the speed and amount of photochemical production of ozone.Vertical temperature gradient influences the vertical mixing in the atmosphere and thereafter the ozone concentration near the ground.Surface winds control the concentrations in mountain valleys and coastal areas.Aloft winds are responsible for the Note: #The level of ozone is expressed as μg/m3 by multiplying ppb by a factor of 2 *Accumulated exposure over a cut-off threshold of 40 ppb ^Mixing ratio is defined as the ratio of the number of molecules of a particular trace gas to the number of molecules of all the other gases present in a given volume of air most parts of the country, the levels are maximum either during daytime or noon and minimum during night time or early morning.

Highest ozone levels in India
In India, the highest level of ground level ozone has been reported in number of individual studies.But the regional variations of ozone are difficult to document as these studies are done at different stations in varying time points and have used different measures to report the highest level.Still in many locations the 8 hourly ozone levels exceeded the recommended 100 μg/m3 as shown in Table 2.

Health effects of Ozone: global literature
Pathological and functional changes in the lung Ozone has been shown to alter epithelial permeability of the lung after 18-20 hours of exposure. 38The lung's mucociliary function is also acutely stimulated by ozone. 39These effects can increase susceptibility to bacterial respiratory infections.Exposure to ambient levels of ozone for 6.6 hours has been shown to increase the markers of inflammation like the Neutrophils (PMNs), Prostaglandin E2 (PGE2), fibronectin, Interleukin-6 (IL-6), and Lactate Dehydrogenase (LDH), alpha-1 antitrypsin in the lungs, and decrease phagocytosis via the complement receptor. 40Short-term exposures to ambient-level O 3 concentrations cause drop in lung function measures such as lung volume and expiratory flow rates, forced vital capacity and specific airway conductance. 41The APHEA (Air Pollution and Health, a European Approach) project in 1997 by Andersen et al in 6 European cities showed there was an increase in hospital admissions for Chronic Obstructive Pulmonary Diseases (COPD ) for all ages for a 50 μ/m 3 change in ozone (RR=1.04). 42rtality A meta-analysis of time series studies and panel studies by WHO in 2004 showed that there was a 0.44% increase in daily mortality per 10 ppb change in 1-hour maximum ozone concentration. 43Similarly a metaanalysis of 50 time-series analyses by Levy et al in 2001 showed a 0.39% change in daily mortality per 10 ppb change in daily 1-hour maximum ozone. 44The APHEA project in 15 European cities by Touloumi et al in 1997 showed that increases of 50 μg/m 3 in O 3 (1-hour maximum) was associated with a 2.9% increase in the daily number of deaths. 45The APHEA 2 project by Gryparis et al in 23 cities/areas for 3 years since 1990 showed that an increase in 1-hour ozone concentration by 10 μg/m 3 was associated with a 0.33% increase in the daily number of deaths, 0.45% in the number of cardiovascular deaths, and 1.13% in the number of respiratory deaths. 46ild health Young children are sensitive to O 3 , because significant lung development continues in the postnatal period. 47Burnett et al demonstrated that in children under 2 years of age, there was a 6.6% increase in hospital admissions per 10 ppb change in 1-hour daily maximum ozone (RR = 1.348). 48Thurston et al showed that among children aged 7 to 13 years in summer asthma camps in New York City, an increase in the 1-hour daily maximal ozone concentration from 84 to 160 ppb was associated with increased unscheduled medications administered per day. 49he health effects of ozone are summarised in Table 3.

Health effects of Ozone: Indian literature
Studies on health effects of ozone from India are limited.Gupta et al demonstrated a significant increase in daily hospital admission for respiratory diseases with elevated levels of ozone. 50Kumar et al conducted a cross-sectional study in Punjab and showed that levels of ozone were found to be higher in an industrial town than in the a non-industrial town and that residence in the industrial town was associated with increased chronic respiratory symptoms like cough, phlegm, breathlessness, or wheezing (OR= 1.5) and spirometric ventilatory defect (OR = 2.4). 51ayaraman et al in Delhi showed that a 10-microgram rise in O 3 led to increase in respiratory morbidity (RR = 1.03). 52

Control of ozone pollution
Through global climate policies, it is estimated that in the time horizon up to 2050, a decrease of ozone concentrations might save nearly 20,000 cases of premature death per year. 53The annual monetary value of health benefits from reducing ozone concentration was estimated to be $10 per person per microgram per cubic meter reduction. 44Steps that are needed to reduce ground-level ozone are as follows: Legal

Role of individuals and NGOs in controlling Ozone level
The public can also reduce ozone levels by conserving energy at home and at work; by reducing vehicle by walking, cycling or using public transportation whenever possible, following gasoline-refueling instructions, keeping motor vehicle engines properly tuned and making sure that tires are properly inflated. 55

CONCLUSIONS
The ground level ozone measured at various stations across the country exceed the threshold limit.Ground level ozone is a health hazard -leading to respiratory and cardio vascular diseases and their exacerbations and adding to the cost of health care of an already strained health system.Policy changes are required to reduce the generation of ground-level ozone and to monitor the ambient levels and health effects.Further studies have to be conducted to measure the mortality and morbidity due to this pollutant in India and the cost of inaction.

Table 2 : Highest ozone level recorded at various stations in India Location Level of ozone [μg/m 3 ]
Surface ozone is regularly monitored by the CPCB through automatic monitoring stations in New Delhi and few other stations.Nevertheless, surface ozone level must also be regularly monitored throughout the country and particularly in rural neighborhoods surrounding large cities as ozone levels are likely to be high in these neighborhoods, particularly because agriculture production is known to be adversely affected by high ozone concentrations.Automobile manufacturing and auto fuel industry can introduce several measures to reduce emissions of precursor pollutants including Vapor Recovery Control, which are systems that control VOC vapour releases during the refuelling of motor vehicles, timely engine turnover, and adoption of cleaner and lower emitting new engines.Similarly, coalburning power plants can adopt clean coal technology to reduce emissions.Urban planners and policy makers can support the cause through improving public transport, reduce congestion on roads, reduce idling time and incentivize use of hybrid or electric vehicles.To reduce vehicular pollution, Honorable Supreme Court of India has ordered the states to strictly implement Emission Norms and to switch over to clean fuels like Compressed Natural Gas (CNG) and Liquefied Petroleum Gas (LPG).Emission standards for the industries are notified under Environment (Protection Act) 1986 to check pollution.The states have given an action plan to the Supreme Court, in which they have given commitment to monitor that the industries are using cleaner fuel, developing green belt and installing pollution control devices.