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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-- October 2006
Summary of preliminary discussions on near-, mid-, and far-field chemistry
W. Brune reporting
• 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.
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
• 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.
• 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.