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MILAGRO Science Workshop -- October 2006 Summary of preliminary discussions on near-, mid-, and far-field chemistry W. Brune reporting. Preliminary Findings Critical needs for moving forward Major research themes to be explored. Major preliminary findings for MCMA photochemistry

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Milagro science workshop october 2006

MILAGRO Science Workshop

-- October 2006

Summary of preliminary discussions on near-, mid-, and far-field chemistry

W. Brune reporting

  • Preliminary Findings

  • Critical needs for moving forward

  • Major research themes to be explored


Milagro science workshop october 2006

Major preliminary findings for MCMA photochemistry

near-field

• The VOC / NOx ratio is shifting toward NOx over time, with increasing NOx and decreasing reactivity. Thus, O3 production is shifting more into the NOx-saturated regime, with potential implications for the value and the timing of the O3 peak.

• The partitioning of NOy is different from that expected. First, the NOx/NOy ratio decreases less rapidly with time than expected. Second, particle nitrate may be a large fraction of total NOy.

• Low temperature combustion of nitrogen-containing fuels is impacting the air quality in the Mexico City area.

• While secondary organic components are a large fraction of typical aerosol particles, crustal material is significant even in Mexico City, where it may affect the gas-phase chemistry.

• Trends appear to be significant in a number of atmospheric gaseous constituents in Mexico City. Determining these trends on multi-year timescales will require the year-to-year variability of the meteorology during the intensive sampling periods.


Milagro science workshop october 2006

Major preliminary findings for MCMA photochemistry

mid-field and far-field

• Pollution over the Gulf of Mexico is persistent and is apparently derived from diverse sources over the SE US, Mexico, and Central America.

• Propane and toluene are good tracers for MCMA. Tracers of biomass burning (e.g., HCN and CH3Cl ) are enhanced both within MCMA and the surrounding region.

• H-1211, previously thought to indicate Asian origin, was detected in MCMA.

• Several MCMA plume encounters over the Gulf exhibited enhanced ozone and continued to produce ozone well downstream.

• Sulfate aerosol increased relative to HNO3 in older polluted air.

• AMS data for C-130 demonstrate the dominance of organics


Milagro science workshop october 2006

  • Critical needs to move forward. We need …

  • the full speciation of VOCs and OVOCs, for photochemical modeling and for emission source identification;

  • • merges of data sets as soon as possible, including meteorology, and a range of models;

  • • meteorology data from observations & models, to understand variations of atmospheric constituents from both the ground sites & aircraft;

  • a geographical and trajectory-based flag system, to associate aircraft merge data with specific source locations;

  • links between near-field and far-field observations; finding key observational connections;

  • a centralize webpage to summarize all dataportals and information to access them;

  • a tabulation of “pseudo-Lagrangian” encounters between all aircraft & 1 and 2 day encounters of the same airmass;

  • the examination of the partitioning of nitrogen between the gas and aerosol phase.


Milagro science workshop october 2006

  • Research themes & potential papers …

  • Quantifying the contributions of biomass burning to the total MCMA urban plume.

  • • Using weekend / weekday differences in many constituents to learn more about the photochemistry.

  • • Comparing and combining VOC, OVOC, and inorganic gas observations from ground-based and aircraft to better understand the sources of the emissions and the distributions of these gases and their products throughout MCMA.

  • • Comparing satellite, ground-based, and aircraft measurements of glyoxal, formaldehyde, and NO2 – both in situ and column measurements.

  • • Putting the ground-based data set, including both in situ and column measurements, and aircraft data sets, including DIAL and in situ sampling, together to learn more about the emissions, meteorology, and chemistry in Mexico City.

  • • Comparing the missed approaches at Mexico City and Monterey.


Milagro science workshop october 2006

Research themes & potential papers …, cont.

• Examining the ground-based and aircraft observations for evidence of meteorological effects, such as the large shift in the meteorology between the early and late parts of the mission?

• Demonstrating the cause of the observed lower ozone in 2006.

• Determining the degree of uniformity of the composition throughout the PBL and its evolution during over a daily cycle.

• Understanding the ozone formation rates and their sensitivity on NOx and VOCs.

• Comparing the observations at TO, T1, and T2 as a quasi-Lagrangian experiment to examine the evolution of the chemical composition (e.g.,18-19 March, 2006).

• Comparing O3/CO ratios from MILAGRO with many previous studies as a tool from understanding chemical evolution from local to regional to global scales.

• Developing a cohesive understanding of the behavior of HOx and NOx radicals in the MCMA region.


Milagro science workshop october 2006

Research themes & potential papers …, cont.

• Model verification of plume propagation

• Plume evolution case studies (multiple platforms) to examine ozone formation efficiency and rate, reactive nitrogen partitioning, VOC evolution, aerosol

• Importance of MCMA versus regional inputs on Gulf of Mexico. Is Mexico City distinguishable downwind? What tracers are good?

• Examination of precursors and oxidation products (e.g., propane, butane versus acetone, MEK, organic nitrates) to find dominant oxidation pathways

• AMS data for C-130 demonstrate the dominance of organics, but other relationships (sulfate/nitrate) are evident as well. HCN correlation with organic aerosol needs to be examined.

• Examining the spatial and temporal distribution of MCMA outflow over the Gulf. Preliminary perception is that pollution over the Gulf from the DC-8 was limited to lower altitudes (< 4km). In contrast, C-130 plume encounters on 19 & 23 March were > 4 km.


Milagro science workshop october 2006

  • Research themes & potential papers …, cont.

  • • Satellite observations need to be integrated into far-field interpretation

  • • The Gulf of Mexico appears to be a diverse mixture from SE US, Mexico, Central American fires, etc.

  • For example, persistence of elevated CH2O (and other oxidation products) far downwind over Gulf of Mexico. Is it MCMA? How much does it contribute versus regional burning?

  • The C-130 plume on 19 March to convincingly show far-field influence of MCMA (need to examine DC-8 data for same day). Also, high SO2 up to 4 km across entire Gulf. Source attribution problem.

  • • Does MCMA contribute to coastal plain pollution to the northeast? (WRF, DC8, C130)