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4 1. Air and ater Pollution W

recent information on the health effects of air pollution hae been summarized in a report v
released by the orld Health Organization (WHO, 2004). W
Regional
Regional air pollution (50–1000 km) can be attributed to two mechanisms:

• transport and dispersion of urban pollutants in large areas,
• transport and transformation of primary pollutants into secondary ones at the regional level.
Two types of air pollution are connected to these mechanisms. The first problem is the for-
mation of tropospheric ozone due to the action of sunlight on mixtures of NO x and VOCs.
Tropospheric ozone is either formed in urban areas and transferred by the wind to rural areas
or formed during the transfer of NO x and VOCs from cities to rural areas by the wind and
has adverse effects on crop yields and human health as well as forest ecosystems (ApSimon
and Warren, 1996). About 90% of the adverse impact of air pollution on agriculture is attribu-
ted to ozone. The second problem is associated with acidifying substances, such as SO 2 ,N O ,
and NO 2 , which are photooxidized in the atmosphere and taken up by cloud droplets, being
thus transformed into the corresponding acids, causing acidification through acid rain for-
mation or dry deposition (direct contact of acids with land and aquatic surfaces by means of
wind), which constitutes an immediate danger for land and aquatic biota (Figure 1.1).

Transboundary
Transboundary air pollution is related to the transfer of air pollution from one country to
another. Generally, the problems that appear on a regional leel may also be e v xchanged

Figure 1.1 The mechanism of acid deposition (ApSimon and 1996). arren, W