Chemistry Reference
In-Depth Information
1
Introduction
Particles in the atmosphere arise from natural sources, such as windborne dust, sea
spray and volcanoes, and from anthropogenic activities, such as combustion of
fuels. Emitted directly as particles (primary aerosol) or formed in the atmosphere by
gas-to-particle conversion processes (secondary aerosol), atmospheric aerosols are
generally considered to be the particles that range in from a few nanometres to tens
of micrometres in diameter [
1
].
Increased understanding of the health issues associated with high concentrations
of particulate matter (PM) have contributed to the identification of PM as the reason
for one of the most critical air pollution problems nowadays. Estimates from the
European Environment Agency [
2
] indicate that exposure to PM causes approxi-
mately three million deaths per year in the world. PM exceedances to the European
Directive 2008/50/EC [
3
] thresholds have been reported by the majority of the
European Union (EU) member countries, mainly in urban agglomerations, where
human exposure is also higher [
4
]. Fine particulates (PM
2.5
) are considered to be
responsible for increased mortality over Europe. Anthropogenic PM
2.5
levels are
expected to be responsible for a loss of 10 months of life expectancy in some
regions of Europe by 2020, in spite of application of the current legislation devoted
to air pollution control [
5
]. It is also recognised that adverse effects from PM long-
term exposure occur whatever the concentration levels are [
6
,
7
].
Health effects of air pollution, namely of PM levels in the air, are the result of a
chain of events, going from the release of pollutants leading to an ambient atmo-
spheric concentration, over the personal exposure, uptake, and resulting internal
dose to the subsequent health effect (Fig.
1
).
The conditions for these events vary considerably and have to be accounted for,
in order to ensure a proper assessment [
8
]. Ambient concentrations and exposure
are the stages of the chain that are mainly covered within this chapter.
Human exposure refers to the individual contact (not uptake) with a pollutant
concentration. It is, then, important to distinguish between concentration and
exposure. According to Sexton and Ryan [
9
] concentration is a physical character-
istic of the environment at a certain place and time (amount of material per unit
volume of air), while the term exposure stands for the interaction between the
environment and a living subject. For exposure to take place two events need to
occur simultaneously: pollution concentration at a particular time and place, and the
presence of a person in that same place and time. Thus exposure has the dimension
of “(mass)
(time)/(volume)”.
Exposure studies can be carried out aiming to estimate exposure of one individ-
ual (personal exposure) or of a larger population group (population exposure),
through direct or indirect methods. Direct methods are measurements made by
personal portable exposure monitors. The personal exposure monitoring devices
that people carry with them must be lightweight, silent, highly autonomous and
