274
Air Pollution and Turbulence: Modeling and Applications
formed from glyoxal is lumped with the rest of the higher PAN analogues. Isoprene
photooxidation products in the mechanism are included. SAPRC uses a condensed
representation of the reactive organic oxidation products and a highly condensed
representation of peroxy reactions.
Jimenez et al. (2003) and Ferreira et al. (2003) have presented comparative studies of different chemical mechanisms in use to simulate photochemical pollution.
Their results verify that, even with most chemical schemes yielding similar ozone
concentrations, there are still signifi cant discrepancies between the different mechanisms tested. It was not possible to conclude which mechanism is more adequate,
but the results did show that a more sophisticated mechanism, with a more complete
description of photochemical reactions, does not mean more accurate results.
Moreover, CTM models aiming to quantify the complex nonlinear relationship
between the emissions of primary precursors and the maximum ground-level concentrations of O 3 require the input of a number of parameters that are currently either
poorly defi ned and/or contain a high degree of uncertainty (Borrego et al., 2000a).
One of the main questions is related to the VOC speciation, meaning that hydrocarbon species have to be treated species by species. There are already some typical
VOC class distributions where biogenic hydrocarbon sources should be taken into
account. An example of disaggregation factors for VOC species considered in CB-IV
chemical mechanism is provided by Zlatev et al. (1993).
10.3 CASE STUDY
High levels of photochemical pollutants, such as ozone, often affect south European
countries and concern with this issue has increased substantially during the last
decade. The west coast of the Iberian Peninsula, surrounded by the Atlantic Ocean,
is characterized by complex topography and some favorable synoptical situations
that promote the occurrence of mesoscale circulations, namely, sea/land breezes and
anabatic and katabatic fl ows (Millan et al., 1992; Carvalho et al., 2006). This type of
circulation encourages photochemical production of air pollutants leading to smog
episodes, which can cause health problems in the population as well as environmental degradation. On the west coast of Portugal, the most densely populated part of
the country, several episodes of photochemical pollution have been verifi ed (Borrego
et al., 2000b).
The European Directive 2002/3/CE relating to ozone in ambient air has been
transposed into Portuguese legislation by Decreto-Lei 320/2003. It establishes the
public information and alert thresholds for human health as being, respectively, set
at 180 and 240 mg m −3 as hourly averages. Additionally, and according to the Air
Quality Framework Directive ([96/62/CE] transposed by Decreto-Lei 276/99), plans
and programs should be implemented in zones and agglomerations where the ozone
concentrations exceed these thresholds, in order to guarantee that in the future they
will be attained.
Notwithstanding the necessary plans and programs, other actions to reduce atmospheric pollutant emissions are foreseen. At the community level, the “National
Emission Ceilings” (NEC) Directive was adopted in 2001 in order to limit the negative environmental impacts of acidifi cation, eutrophication, and ground-level ozone
© 2010 by Taylor and Francis Group, LLC
Air Pollution and Turbulence: Modeling and Applications
formed from glyoxal is lumped with the rest of the higher PAN analogues. Isoprene
photooxidation products in the mechanism are included. SAPRC uses a condensed
representation of the reactive organic oxidation products and a highly condensed
representation of peroxy reactions.
Jimenez et al. (2003) and Ferreira et al. (2003) have presented comparative studies of different chemical mechanisms in use to simulate photochemical pollution.
Their results verify that, even with most chemical schemes yielding similar ozone
concentrations, there are still signifi cant discrepancies between the different mechanisms tested. It was not possible to conclude which mechanism is more adequate,
but the results did show that a more sophisticated mechanism, with a more complete
description of photochemical reactions, does not mean more accurate results.
Moreover, CTM models aiming to quantify the complex nonlinear relationship
between the emissions of primary precursors and the maximum ground-level concentrations of O 3 require the input of a number of parameters that are currently either
poorly defi ned and/or contain a high degree of uncertainty (Borrego et al., 2000a).
One of the main questions is related to the VOC speciation, meaning that hydrocarbon species have to be treated species by species. There are already some typical
VOC class distributions where biogenic hydrocarbon sources should be taken into
account. An example of disaggregation factors for VOC species considered in CB-IV
chemical mechanism is provided by Zlatev et al. (1993).
10.3 CASE STUDY
High levels of photochemical pollutants, such as ozone, often affect south European
countries and concern with this issue has increased substantially during the last
decade. The west coast of the Iberian Peninsula, surrounded by the Atlantic Ocean,
is characterized by complex topography and some favorable synoptical situations
that promote the occurrence of mesoscale circulations, namely, sea/land breezes and
anabatic and katabatic fl ows (Millan et al., 1992; Carvalho et al., 2006). This type of
circulation encourages photochemical production of air pollutants leading to smog
episodes, which can cause health problems in the population as well as environmental degradation. On the west coast of Portugal, the most densely populated part of
the country, several episodes of photochemical pollution have been verifi ed (Borrego
et al., 2000b).
The European Directive 2002/3/CE relating to ozone in ambient air has been
transposed into Portuguese legislation by Decreto-Lei 320/2003. It establishes the
public information and alert thresholds for human health as being, respectively, set
at 180 and 240 mg m −3 as hourly averages. Additionally, and according to the Air
Quality Framework Directive ([96/62/CE] transposed by Decreto-Lei 276/99), plans
and programs should be implemented in zones and agglomerations where the ozone
concentrations exceed these thresholds, in order to guarantee that in the future they
will be attained.
Notwithstanding the necessary plans and programs, other actions to reduce atmospheric pollutant emissions are foreseen. At the community level, the “National
Emission Ceilings” (NEC) Directive was adopted in 2001 in order to limit the negative environmental impacts of acidifi cation, eutrophication, and ground-level ozone
© 2010 by Taylor and Francis Group, LLC