132
L. T. Molina et al.
Earlier modeling studies suggested that O 3 production within the MCMA is generally VOC-limited. However, potential changes in VOC/NO x ratios resulting from
variations in VOC composition and contributions from key emission sources driven
by recent technological and regulatory changes in the MCMA highlight the need to
update our understanding of O 3 formation. Under a VOC-limited regime, reduction
of VOCs could effectively reduce O 3 formation in the MCMA; reductions of NO x
emissions would not be as effective locally, but may reduce O 3 production at the
regional scale. Long-range export of reactive nitrogen from Mexico City occurred
primarily through the formation of peroxyacetyl nitrates (PANs), which can thermally decompose, regenerate NO x and contribute to regional O 3 formation. The
production of O 3 (a potent greenhouse gas) continued in the outflow for several days
with potential climate impact.
The deployment of multiple instrumentation and sampling techniques in different
sites during the MCMA-2003 and MILAGRO field campaigns provided a wealth of
knowledge on the chemical composition and physical properties of different types
of aerosols, including dust, biomass burning, and anthropogenic emissions and their
chemical transformation. One of the main results was the observation during MCMA2003 that secondary organic aerosol (SOA) production was higher than previously
predicted with traditional SOA models, triggering active research for updating SOA
formation mechanisms. SOA accounts for a large fraction of the organic aerosol
burden; the formation, evolution, and climate impacts of SOA (and organic aerosols)
remain one of the least understood aspects in atmospheric science and are important
current research topics.
The results from the field studies and policy implications were presented to the
Mexican authorities and were included in the current Air Quality Management
Program (PROARE 2011–2020). Some of the key policy actions that the government has reinforced include: strengthening the controls of vehicular emissions with
advanced technologies and fuel reformulation, diesel vehicles self-regulation program, enhancement of the mandatory vehicle inspection and maintenance program
and the atmospheric environmental contingency program, improved public transportation and bike-sharing program. Recently, with the collaboration of Barcelona
Supercomputing Center, the Mexico City government has developed an air quality
forecasting system to alert the public of high pollution event 24 h in advance, as well
as in evaluating emission reduction policies for air quality improvement and other
co-benefits (climate, food security, etc.).
21.2.2 Central Mexico Megalopolis
MILAGRO was planned to investigate the evolution of emission plumes from megacities. All large cities emit large amounts of pollutants from multiple local sources
that combine with emissions from neighboring cities. Mexico City was the dominant
city in central Mexico and MILAGRO provided an opportunity to follow the urban
emission plumes from the city center and to study how they change with time and
L. T. Molina et al.
Earlier modeling studies suggested that O 3 production within the MCMA is generally VOC-limited. However, potential changes in VOC/NO x ratios resulting from
variations in VOC composition and contributions from key emission sources driven
by recent technological and regulatory changes in the MCMA highlight the need to
update our understanding of O 3 formation. Under a VOC-limited regime, reduction
of VOCs could effectively reduce O 3 formation in the MCMA; reductions of NO x
emissions would not be as effective locally, but may reduce O 3 production at the
regional scale. Long-range export of reactive nitrogen from Mexico City occurred
primarily through the formation of peroxyacetyl nitrates (PANs), which can thermally decompose, regenerate NO x and contribute to regional O 3 formation. The
production of O 3 (a potent greenhouse gas) continued in the outflow for several days
with potential climate impact.
The deployment of multiple instrumentation and sampling techniques in different
sites during the MCMA-2003 and MILAGRO field campaigns provided a wealth of
knowledge on the chemical composition and physical properties of different types
of aerosols, including dust, biomass burning, and anthropogenic emissions and their
chemical transformation. One of the main results was the observation during MCMA2003 that secondary organic aerosol (SOA) production was higher than previously
predicted with traditional SOA models, triggering active research for updating SOA
formation mechanisms. SOA accounts for a large fraction of the organic aerosol
burden; the formation, evolution, and climate impacts of SOA (and organic aerosols)
remain one of the least understood aspects in atmospheric science and are important
current research topics.
The results from the field studies and policy implications were presented to the
Mexican authorities and were included in the current Air Quality Management
Program (PROARE 2011–2020). Some of the key policy actions that the government has reinforced include: strengthening the controls of vehicular emissions with
advanced technologies and fuel reformulation, diesel vehicles self-regulation program, enhancement of the mandatory vehicle inspection and maintenance program
and the atmospheric environmental contingency program, improved public transportation and bike-sharing program. Recently, with the collaboration of Barcelona
Supercomputing Center, the Mexico City government has developed an air quality
forecasting system to alert the public of high pollution event 24 h in advance, as well
as in evaluating emission reduction policies for air quality improvement and other
co-benefits (climate, food security, etc.).
21.2.2 Central Mexico Megalopolis
MILAGRO was planned to investigate the evolution of emission plumes from megacities. All large cities emit large amounts of pollutants from multiple local sources
that combine with emissions from neighboring cities. Mexico City was the dominant
city in central Mexico and MILAGRO provided an opportunity to follow the urban
emission plumes from the city center and to study how they change with time and