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Air Pollution Ozone

1. What is Ozone (O3)

    The source document for this Digest states:

    Ozone is the most important photochemical oxidant in the troposphere. It is formed by photochemical reactions in the presence of precursor pollutants such as NOx and volatile organic compounds. In the vicinity of strong NOx emission sources, where there is an abundance of NO, O3 is “scavenged” and as a result its concentrations are often low in busy urban centres and higher in suburban and adjacent rural areas. On the other hand, O3 is also subject to long-range atmospheric transport and is therefore considered as a trans-boundary problem.

    As a result of its photochemical origin, O3 displays strong seasonal and diurnal patterns, with higher concentrations in summer and in the afternoon. The correlation of O3 with other pollutants varies by season and location.

    There is evidence from controlled human and animal exposure studies of the potential for O3 to cause adverse health effects. Epidemiological studies have also addressed the effects of short and long-term exposures to O3 and provided important results. However, the health effects of O3 have been less studied than those of PM and thus more research is needed, especially addressing the spatial and seasonal patterns and misclassification of individual exposure in association with health outcomes.

    Source & ©: WHO Regional Office for Europe  "Health Aspects of Air Pollution" (2003), Chapter 6 Ozone (O3), Section 6.1 Introduction

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