A42A-01
A Brief Overview of INTEX-B and OVOC Observations Over Mexico City, Gulf of Mexico, and the Pacific Ocean
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
A42A-02
Observations of Reactive Nitrogen over the North Pacific: Comparisons, Implications and Chemical Constraints
Observations of the partitioning, magnitude and distribution of reactive nitrogen, over the Northern Pacific Ocean, are used to investigate the role of increasing Asian NOx emissions and their subsequent impact on the photochemical state of the Northern Pacific Ocean and the flux of pollution transported to North America. These results reveal a meridional dependence of the vertical distribution of NOy. Specifically, our observations show that PAN plays a strong role in the redistribution of NOx and has a significant impact on the O3 budget of the remote Pacific.
A42A-03
Trans-Pacific Transport of Asian Dust During INTEX B
NASA's tropospheric chemistry program has deployed the DC-8 airborne laboratory to the northern Pacific four times since 1991 to study Asian outflow. During the most recent campaign (INTEX B in Spring 2006) sorties were conducted from Hawaii and Alaska to intercept Asian plumes several days or more downwind of the continent. Previous missions (PEM West A and B, TRACE P) sampled similar regions over the central and eastern north Pacific, but also included flights from Japan and Hong Kong targeting fresher Asian emissions. Enhancements of non-seasalt aerosol-associated Ca2+ were encountered throughout the depth of the troposphere on nearly all INTEX B flights over the Pacific, contrasting much lower dust loadings in these regions in the earlier campaigns. INTEX B dust plumes were generally associated with enhanced levels of aerosol NO3-, consistent with previous observations of uptake of HNO3 by Asian dust immediately downwind of Asia (e.g., during TRACE P and ACE Asia). Enhancements of non-seasalt SO4= also characterized many of the INTEX B dust plumes, reflecting long-range transport of a mixture of dust and pollution from Asia eastward. The increase in observed dust over the remote Pacific during INTEX B compared to TRACE P may be partly due to more favorable transport, but also reflects increasing emissions from Asian source regions.
A42A-04
HOx Chemistry and Ozone Production During INTEX-B
Measurements of OH and HO2 (collectively called HOx) were made with the Airborne Tropospheric Hydrogen Oxides Sensor (ATHOS) as part of a much larger measurement suit from the NASA DC-8 aircraft during INTEX-B in spring 2006. This mission, which was conducted mainly over South United State and Mexico (Phase- A) and West Pacific Ocean (Phase-B), was an excellent test of oxidation chemistry in pollution plumes and clean air throughout the troposphere. Measured HOx are compared with the calculations from a box model constrained to other in-situ measurements of long-lived chemicals. On average, both the measured OH and HO2 agree well with the calculations within 15%, which is similar to the results during INTEX-A, another aircraft mission conducted over the continental of the United States, except above 8 km where the model significantly under-predicted HO2 during INTEX-A. The main HOx production was the O(1D)+H2O reaction and main HOx loss was the HO2+HO2 and HO2+RO2 reactions. During Phase-A, there was a net O3 production rate (0.1-1 ppb/hr) below 4 km, while during Phase-B a slight net O3 loss rate (0.1-0 ppb/hr) below 7 km and a slight net O3 production rate (0-0.1 ppb/hr) above 7 km were observed. HOx behavior under different conditions will be discussed.
A42A-05
Photochemistry Within Plumes of Various Origin During INTEX-B: A Case Study From May 5
INTEX-B provided the opportunity to directly sample pollution plumes of Asian origin during their transport across the northern Pacific Ocean in the spring of 2006. On May 5, the C130 aircraft flew several vertical profiles during a transect off the western North American coast through a series of distinct plumes. These plumes are analyzed using high resolution data and trajectory information with a focus on enhancement correlations between various species and transport history. We find that elevated O3 in these plumes is the result of transport from a combination several distinct source regions, including highly polluted air off the Asian coast and background middle to high tropospheric air originating over the northern Pacific. A photochemical box model is used to examine photochemical signatures such as O3 production tendencies and NOy partitioning within these mixed plumes. The results are presented relative to the overall predictions of the O3 budget over the northern Pacific using data obtained from both the DC8 and the C130 aircraft through the duration of the mission.
A42A-06
Large-Scale Ozone and Aerosol Variations Observed Over the Pacific Ocean During the INTEX-B Field Experiment
Large-scale distributions of ozone and aerosols were measured with a differential absorption lidar (DIAL) on the NASA DC-8 aircraft during the second part of the Intercontinental Chemical Transport Experiment - Phase B (INTEX-B) field experiment conducted over the Pacific Ocean from 17 April to 15 May 2006. Remote ozone and aerosol profiles were simultaneously measured below and above the DC-8 to provide information from near the surface to above the tropopause along the flight track. Multiple-wavelength aerosol backscatter measurements were made to estimate the relative size of the aerosols, and simultaneous aerosol depolarization measurements were made to detect the presence of nonspherical aerosols, such as mineral dust. In situ measurements of ozone were also made onboard the DC-8, and these were used to constrain the interpolation of the nadir and zenith ozone lidar measurements, which then provided an estimate of the entire tropospheric ozone profile along the flight track. Large-scale measurements of tropospheric ozone and aerosol distributions were obtained on all INTEX-B flights over the Pacific, and the long-range transport of aged and relatively fresh Asian pollution was often observed in the free troposphere in eastern Pacific. Comparisons have been made between the measured ozone cross sections and results from chemical transport models, which show general agreement in the atmospheric structure and pollution layer features. Average latitudinal and longitudinal variations of ozone and aerosols have also been derived from the remote and in situ ozone data for INTEX-B, and these results are compared to previous field experiments. The contribution of stratosphere-troposphere exchange to the latitudinal variation of ozone over the Pacific has also been examined. This paper discusses these results and relates them to chemical and dynamical processes that produce the observed large-scale variations in ozone and aerosols over the Pacific.
A42A-07
Contrast Between the Sources and Atmospheric Processing of Fine Particles from Asia and North America Measured During INTEX B
During the Intercontinental Chemical Transport Experiment, Phase B (INTEX B), conducted in the spring of 2006, airborne measurements were made in the United States Pacific Northwest of the major inorganic ions and the water-soluble organic carbon (WSOC) of submicron (PM1.0) aerosol. An atmospheric trajectory and a particle dispersion model for CO sources (Flexpart) was used to segregate air masses into those of primarily Asian influence (greater than 75 percent Asian CO) or North American influence (greater than 75 percent North American CO). Measured components of fine particle mass mostly consisted of water-soluble organic carbon and sulfate, with highest median WSOC and sulfate concentrations in North American air masses. Curiously, the fraction of sulfate to WSOC was significantly higher at altitudes above 3 km, opposite to what has been observed closer to Asia and in the northeastern United States. The observations could be explained by loss of sulfate and organic aerosol due to precipitation scavenging near Asia, with reformation of only sulfate during advection from Asia to North America. WSOC sources were investigated by multivariate linear regression analyses of volatile organic compounds (VOCs). In Asian air masses detected over the Pacific Northwest, of the WSOC variability that could be explained (49 percent), most was related to fossil fuel combustion VOCs, compared to North American air masses, where 75 percent of the WSOC variability was explained through a nearly equal combination of fossil fuel combustion and biogenic VOCs. The most distinct WSOC plumes of the mission were from the California Central Valley, where WSOC variability was related to a mix of biogenic and anthropogenic VOCs. These plumes appeared to be related to secondary organic aerosol formation associated with cloud processing.
A42A-08
Quasi-Lagrangian Chemical Sampling during INTEX-B
Lagrangian sampling requires taking in situ measurements of an air parcel, followed by later sampling of that same parcel after it has moved to a new location. This sampling is virtually impossible to achieve for atmospheric parcels; however, a quasi-Lagrangian approach is more feasible. Quasi-Lagrangian sampling involves taking measurements of a parcel at one location, and later sampling of what is believed to be the same, or a very similar parcel, at a different location. A goal of the Intercontinental Chemical Transport Experiment—Phase B (INTEX-B) was to perform quasi-Lagrangian sampling of pollution plumes traveling from Asia toward the United States. Initial chemical measurements during INTEX-B were taken by NASA's DC-8 flying laboratory during flights out of Anchorage, AK. The subsequent, downwind measurements were taken by NCAR's C-130 aircraft during flights out of Seattle, WA. We determined quasi-Lagrangian sampling by creating back trajectories at 1 min intervals along all the C-130 flight tracks. As each trajectory moved back in time, it was continually checked against navigation data of the DC-8 flight being considered. If the trajectory came within 1 deg lat/long, 50 mb, and 1 hour of any location along the DC-8's flight track, quasi-Lagrangian sampling was assumed. Although these thresholds seem reasonable based on trajectory uncertainty, they are subject to revision. The periods between quasi-Lagrangian sampling ranged from one to four days, with the parcels traveling in the lower, middle, and upper troposphere. Usually there were several quasi-Lagrangian sampling periods during each pair of flights. The paper will list the INTEX-B flight legs during which quasi-Lagrangian chemical sampling was achieved, describe the origins and paths taken by the sampled air, and describe the meteorological evolutions that occurred between the origins of the air, its initial sampling by the DC-8, and later sampling by the C-130. Follow- on chemical modeling that will be conducted in collaboration with NASA Langley Research Center also will be described.