The Amazon Basin plays key role in atmospheric chemistry, biodiversity and climate change. In this study we applied nanoelectrospray (nanoESI) ultra-high-resolution mass spectrometry (UHRMS) for the analysis of the organic fraction of PM_2.5 aerosol samples collected during dry and wet seasons at a site in central Amazonia receiving background air masses, biomass burning and urban pollution. Comprehensive mass spectral data evaluation methods (e.g. Kendrick mass defect, Van Krevelen diagrams, carbon oxidation state and aromaticity equivalent) were used to identify compound classes and mass distributions of the detected species. Nitrogen- and/or sulfur-containing organic species contributed up to 60 % of the total identified number of formulae. A large number of molecular formulae in organic aerosol (OA) were attributed to later-generation nitrogen- and sulfur-containing oxidation products, suggesting that OA composition is affected by biomass burning and other, potentially anthropogenic, sources. Isoprene-derived organosulfate (IEPOX-OS) was found to be the most dominant ion in most of the analysed samples and strongly followed the concentration trends of the gas-phase anthropogenic tracers confirming its mixed anthropogenic–biogenic origin. The presence of oxidised aromatic and nitro-aromatic compounds in the samples suggested a strong influence from biomass burning especially during the dry period. Aerosol samples from the dry period and under enhanced biomass burning conditions contained a large number of molecules with high carbon oxidation state and an increased number of aromatic compounds compared to that from the wet period. The results of this work demonstrate that the studied site is influenced not only by biogenic emissions from the forest but also by biomass burning and potentially other anthropogenic emissions from the neighbouring urban environments.

We have carried out studies of the transport between the tropical boundary layer, the tropical tropopause layer, and the stratosphere during January 2001 using both atmospheric tracers in a transport model and air parcel trajectories. Most of the transport (approximately two thirds) from the planetary boundary layer (BL) into the tropical tropopause layer (TTL) occurs vertically above the Indian Ocean and the Indonesian and west Pacific regions, consistent with transport dominated by convection. Transport from the base of the TTL into the stratosphere above the dynamical tropopause is dominated (approximately 95%) by transport into the extratropical lowermost stratosphere (ELS) with a much smaller fraction entering the stratospheric “overworld.” Overall, transport from the BL to the ELS is sufficiently rapid that this represents an important route by which very short lived substances (VSLS), emitted at the surface, can influence lower stratospheric ozone. The two approaches, using high‐resolution trajectories and a lower‐resolution transport model, yield generally similar results, increasing confidence that chemistry transport models can capture transport sufficiently well for chemical assessment modeling of the role of VSLS.

[1] A global chemistry‐climate model is used to assess the impact on atmospheric composition of the regeneration and recycling of HO_x in the photo‐oxidation of isoprene. The impact is explored subject to present‐day, pre‐industrial and future climate/emission scenarios. Our calculations show that, in all cases, the inclusion of uni‐molecular isomerisations of the isoprene hydroxy‐peroxy radicals leads to enhanced production of HO_x radicals and ozone. The global burden of ozone increases by 25–36 Tg (8–18%), depending on the climate/emissions scenario, whilst the changes in OH lead to decreases in the methane lifetime of between 11% in the future and 35% in the pre‐industrial. Critically the size of the change in methane lifetime depends on the VOC/NO_x emission ratio. The results of the present‐day calculations suggest a certain amount of parameter refinement is still needed to reconcile the updated chemistry with field observations (particularly for HO₂+RO₂). However, the updated chemistry could have far‐reaching implications for: future‐climate predictions; projections of future oxidising capacity; and our understanding of past changes in oxidising capacity.

Sea ice is a reflection of, and a feedback on, the Earth's climate. We explore here, using a global atmospheric chemistry‐transport model, the use of sea salt in Antarctic ice cores to obtain continuous long‐term, regionally integrated records of past sea ice extent, synchronous with ice core records of climate. The model includes the production, transport, and deposition of sea salt aerosol from the open ocean and “blowing snow” on sea ice. Under current climate conditions, we find that meteorology, not sea ice extent, is the dominant control on the atmospheric concentration of sea salt reaching coastal and continental Antarctic sites on interannual timescales. However, through a series of idealized sensitivity experiments, we demonstrate that sea salt has potential as a proxy for larger changes in sea ice extent (e.g., glacial‐interglacial). Treating much of the sea ice under glacial conditions as a source of salty blowing snow, we demonstrate that the increase in sea ice extent alone (without changing the meteorology) could drive, for instance, a 68% increase in atmospheric sea salt concentration at the site of the Dome C ice core, which exhibits an approximate twofold glacial increase in sea salt flux. We also show how the sensitivity of this potential proxy decreases toward glacial sea ice extent—the basis of an explanation previously proposed for the lag observed between changes in sea salt flux and δD (an ice core proxy for air temperature) at glacial terminations. The data thereby permit simultaneous changes in sea ice extent and climate.

Intercontinental Transport of Ozone and Precursors (ITOP) (part of International Consortium for Atmospheric Research on Transport and Transformation (ICARTT)) was an intense research effort to measure long‐range transport of pollution across the North Atlantic and its impact on O₃ production. During the aircraft campaign plumes were encountered containing large concentrations of CO plus other tracers and aerosols from forest fires in Alaska and Canada. A chemical transport model, p‐TOMCAT, and new biomass burning emissions inventories are used to study the emissions long‐range transport and their impact on the troposphere O₃ budget. The fire plume structure is modeled well over long distances until it encounters convection over Europe. The CO values within the simulated plumes closely match aircraft measurements near North America and over the Atlantic and have good agreement with MOPITT CO data. O₃ and NO_x values were initially too great in the model plumes. However, by including additional vertical mixing of O₃ above the fires, and using a lower NO₂/CO emission ratio (0.008) for boreal fires, O₃ concentrations are reduced closer to aircraft measurements, with NO₂ closer to SCIAMACHY data. Too little PAN is produced within the simulated plumes, and our VOC scheme's simplicity may be another reason for O₃ and NO_x model‐data discrepancies. In the p‐TOMCAT simulations the fire emissions lead to increased tropospheric O₃ over North America, the north Atlantic and western Europe from photochemical production and transport. The increased O₃ over the Northern Hemisphere in the simulations reaches a peak in July 2004 in the range 2.0 to 6.2 Tg over a baseline of about 150 Tg.