To aid in the analysis and interpretation of the ANTCI data, investigators will use a suite of models that include a time-dependent, photochemical box model implemented both in single and multi-box configurations, a sulfur chemistry model driven by radical calculations from the photochemical box model, and a regional 3-D chemistry and transport model. By focusing on the processes at various scales, these models will be used to complement each other in the pursuit of understanding the details of Antarctic photochemistry and its impact on the delivery of sulfur and nitrogen to the polar plateau.
The photochemical box model will focus on the in situ data, both from the ground and aircraft to understand the details of Antarctic HOx chemistry. This will include the role of NOx as well as other species emitted from the snowpack (e.g., CH2O, H2O2, and HONO). The box model will also be used to estimate surface fluxes for these species. The box model results will be used to feed the sulfur chemistry model to assess in-situ rates of DMS oxidation and product formation at various points between the coast and the polar plateau.
Focusing on the scale of the polar plateau, a multi-box implementation of the photochemical box model will be used to examine the interplay of chemistry and dynamics that result in the observed variability in NO and HNO3. This involves calculating the impact of exchanges between the mixed layer and the lower free troposphere due to changes in mixing depth as air masses travel along the polar plateau.
The results from these models will provide valuable information for simulations of the Antarctic continent and surrounding oceans using a regional 3-D chemistry and transport model. This model will benefit from box model assessments of HOx photochemistry and DMS oxidation as well as estimated surface fluxes for NOx, H2O2, CH2O, and HONO. 3-D simulations will be used to investigate the sources of reactive nitrogen deposited into the snow and the export of reactive nitrogen produced from snow to the free troposphere. Specific attention will be paid to evaluating simulated reactive nitrogen concentrations with the observations. The correlation between reactive nitrogen species and other chemical tracers will be analyzed to identify reactive nitrogen sources. As part of this analysis, chemical tracers with different lifetimes will be simulated to examine transport pathways. The budget of reactive nitrogen and the effects of snow chemistry on tropospheric NOx/HOx/O3 photochemistry at high southern latitudes will be investigated. The oxidation of DMS and transport of the terminal oxidation products (e.g., MS, NSS) will be simulated in the model. The partitioning among SO2, DMSO, and MSA and the MS/NSS ratio will be analyzed as function of the chemical oxidation and transport pathways. Thus, the effects of key branching ratios and scavenging of species can be assessed. The implications of our source apportionment for atmospheric sulfur and nitrogen will be examined in the context of these species use as ice core proxy species for identifying major global geophysical events including major past climate changes.