Non-methane hydrocarbons (NMHCs) and oxygenated volatile organic compounds (OVOCs) were measured aboard the NCAR C-130 during MIRAGE-MEX. Airborne NMHCs result from primary emissions whereas airborne ...OVOCs result from both primary emissions and from the oxidation of NMHC precursors. The photochemical age of air downwind of Mexico City is estimated using an ensemble of VOC measurements and this is compared with back-trajectory estimates. The OVOCs are explored in terms of observed mixing ratios and expected mixing ratios calculated from a box model and from MOZART, a 3-D global chemical transport model. Correlations between various OVOC species, CO, formaldehyde, and NMHCs are examined. Relationships between PAN and acetaldehyde and PPN and propionaldehyde are explored and implications are noted for active photochemistry downwind of Mexico City.
The chemistry and fate of reactive nitrogen emitted from Mexico City is examined. Measurements of NOx, NOy, PANs, alkyl nitrates, HNO3, and particulate nitrate were made on board the NCAR/NSF C-130 ...aircraft during the 2006 MILAGRO campaign. Near- and far-field outflow from the Mexico City metropolitan area was probed by the C-130 ranging from city overflights to a distance of 1000 km from the city. Reactive nitrogen and CO measurements made on board the DOE G-1 aircraft are also used. In addition, Mexico City outflow was successfully tagged by two radio controlled CMET Balloons and the same air was measured on two consecutive days during the March 18/19 outflow event. The reactive nitrogen data is examined with regard to NOy partitioning, ozone formation efficiency, and the ultimate fate of NOy, as a function of time and distance from the city. The NOx sequestration chemistry is examined using the WRF-Chem model. Because of the unique conditions in Mexico City with regard to altitude and climate as well as the high particle loading in the area the chemistry in the Mexico City outflow is very different compared to other mega-cities such as New York City. These differences and the resulting impacts on the region around the city will be discussed.
INTEX-B/MILAGRO* was a major international atmospheric chemistry field campaign completed in the spring of 2006 (March 1-May 15). Airborne measurements of a large number of oxygenated volatile ...organic chemicals (OVOC) were carried out over Mexico City, Gulf of Mexico, and the Pacific Ocean using the NASA DC-8 and NSF/NCAR C-130. OVOC measurements included acetone, methylethyl ketone, methanol, ethanol, acetaldehyde, propanal, formaldehyde, organic peroxides, PANs, and organic nitrates. Complementary measurements of several tracers (CO, HCN) were also made. Throughout the troposphere mixing ratios of several OVOC were strongly correlated with each other as well as with tracers of fossil and biomass/biofuel combustion. The composition of these air masses also indicated a large shift of reactive nitrogen into the PAN reservoir during transport thereby limiting ozone formation. Several 3-D models (GEOS-Chem, MOZART, RAQMS, STEM) were used to simulate these observations with partial success. Some of these OVOC have also been retrieved from satellite observations in the upper troposphere and these data are compared. An analysis of the distribution and sources of OVOC based on INTEX-B/MILAGRO and some satellite observations will be presented. *INTEX-B: Intercontinental Chemical Transport Experiment-B; MILAGRO: Megacity Initiative: Local and Global Research Observations
