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Corrigendum to "Satellite observations and model simulations of tropospheric NO2 columns over south-eastern Europe" published in Atmos. Chem. Phys., 9, 6119–6134, 2009
Limb scatter ozone retrieval from 10 to 60 km using a multiplicative algebraic reconstruction technique

The OSIRIS instrument onboard the Odin spacecraft routinely measures vertical profiles of spectrally dispersed, limb scattered sunlight from the upper troposphere into the lower mesosphere. These measurements are used to retrieve the ozone number density vertical profile using the SaskMART Multiplicative Algebraic Reconstruction Technique, which is a one dimensional modification of an existing two-dimensional tomographic retrieval algorithm. The retrieved profile extends from the cloud top to 60 km. In the absence of clouds the retrieval extends down to 10 km. This technique allows for the consistent merging of the absorption information from radiance measurements at wavelengths in the Chappuis and the Hartley-Huggins bands at each iteration of the inversion. The effectiveness of the retrieval is demonstrated using a set of coincident SAGE II occultation measurements that show a mean bias of less than 2% from 18 to 53 km.
Land use change suppresses precipitation

A feedback loop between regional scale deforestation and climate change was investigated in an experiment using novel, small size airborne platforms and instrument setups. Experiments were performed in a worldwide unique natural laboratory in Western Australia, characterized by two adjacent homogeneous observation areas with distinctly different land use characteristics. Conversion of several ten thousand square km of forests into agricultural land began more than a century ago. Changes in albedo, surface roughness, the soil water budget and the planetary boundary layer evolved over decades. Besides different meteorology, we found a significant up to now overlooked source of aerosol over the agriculture area. The enhanced number of cloud condensation nuclei is coupled through the hydrological groundwater cycle with deforestation. Modification of surface properties and aerosol number concentrations are key factors for the observed reduction of precipitation. The results document the importance of aerosol indirect effects on climate due to nanometer size biogenic aerosol and human impact on aerosol sources.
The formation of secondary organic aerosol from the isoprene + OH reaction in the absence of NOx

The reaction of isoprene (C5H8) with hydroxyl radicals has been studied in the absence of nitrogen oxides (NOx) to determine physical and chemical characteristics of the secondary organic aerosol formed. Experiments were conducted using a smog chamber operated in a steady-state mode permitting measurements of moderately low aerosol levels. GC-MS analysis was conducted to measure methyl butenediols in the gas phase and polyols in the aerosol phase. Analyses were made to obtain several bulk aerosol parameters from the reaction including values for the organic mass to organic carbon ratio, the effective enthalpy of vaporization (ΔHvapeff), organic peroxide fraction, and the aerosol yield. The gas phase analysis showed the presence of methacrolein, methyl vinyl ketone, and four isomers of the methyl butenediols. These gas-phase compounds may serve as precursors for one or more of several compounds detected in the aerosol phase including 2-methylglyceric acid, three 2-methyl alkenetriols, and two 2-methyl tetrols. In contrast to most previous studies, the 2-methyl tetrols (and the 2-methyl alkenetriols) were found to form in the absence of acidic sulfate aerosol. However, reaction conditions did not favor the production of HO2 radicals, thus allowing RO2+RO2 reactions to proceed more readily than if higher HO2 levels had been generated. SOA/SOC (i.e. OM/OC) was found to average 1.9 in the absence of NOx. The effective enthalpy of vaporization was measured as 38.6 kJ mol−1, consistent with values used previously in modeling studies. The yields in this work (using an independent technique than used previously) are lower than those of Kroll et al. (2006) for similar aerosol masses. SOC yields reported in this work range from 0.5–1.4% for carbon masses between 17 and 49 μgC m−3.
Peroxy radicals and ozone photochemistry in air masses undergoing long-range transport

Concentrations of peroxy radicals (HO2+ΣiRiO2) in addition to other trace gases were measured onboard the UK Meteorological Office/Natural Environment Research Council British Aerospace 146-300 atmospheric research aircraft during the Intercontinental Transport of Ozone and Precursors (ITOP) campaign based at Horta Airport, Faial, Azores (38.58° N, 28.72° W) in July/August 2004. The overall peroxy radical altitude profile displays an increase with altitude that is likely to have been impacted by the effects of long-range transport. The peroxy radical altitude profile for air classified as of marine origin shows no discernable altitude profile. A range of air-masses were intercepted with varying source signatures, including those with aged American and Asian signatures, air-masses of biomass burning origin, and those that originated from the east coast of the United States. Enhanced peroxy radical concentrations have been observed within this range of air-masses indicating that long-range transported air-masses traversing the Atlantic show significant photochemical activity. The net ozone production at clear sky limit is in general negative, and as such the summer mid-Atlantic troposphere is at limit net ozone destructive. However, there is clear evidence of positive ozone production even at clear sky limit within air masses undergoing long-range transport, and during ITOP especially between 5 and 5.5 km, which in the main corresponds to a flight that extensively sampled air with a biomass burning signature. Ozone production was NOx limited throughout ITOP, as evidenced by a good correlation (r2=0.72) between P(O3) and NO. Strong positive net ozone production has also been seen in varying source signature air-masses undergoing long-range transport, including but not limited to low-level export events, and export from the east coast of the United States.
The sensitivity of CO and aerosol transport to the temporal and vertical distribution of North American boreal fire emissions

Forest fires in Alaska and western Canada represent important sources of aerosols and trace gases in North America. Among the largest uncertainties when modeling forest fire effects are the timing and injection height of biomass burning emissions. Here we simulate CO and aerosols over North America during the 2004 fire season, using the GEOS-Chem chemical transport model. We apply different temporal distributions and injection height profiles to the biomass burning emissions, and compare model results with satellite-, aircraft-, and ground-based measurements. We find that averaged over the fire season, the use of finer temporal resolved biomass burning emissions usually decreases CO and aerosol concentrations near the fire source region, and often enhances long-range transport. Among the individual temporal constraints, switching from monthly to 8-day time intervals for emissions has the largest effect on CO and aerosol distributions, and shows better agreement with measured day-to-day variability. Injection height substantially modifies the surface concentrations and vertical profiles of pollutants near the source region. Compared with CO, the simulation of black carbon aerosol is more sensitive to the temporal and injection height distribution of emissions. The use of MISR-derived injection heights improves agreement with surface aerosol measurements near the fire source. Our results indicate that the discrepancies between model simulations and MOPITT CO measurements near the Hudson Bay can not be attributed solely to the representation of injection height within the model. Frequent occurrence of strong convection in North America during summer tends to limit the influence of injection height parameterizations of fire emissions in Alaska and western Canada with respect to CO and aerosol distributions over eastern North America.
Regional-scale correlation between CO2 fire emissions, burned areas, and mid-tropospheric CO2 daily variations over southern Africa

Monthly mean mid-tropospheric CO2 columns are retrieved from evening and morning observations of NOAA-10 satellite over the tropics during the period 1987–1991. We find that the difference between evening and morning CO2 columns (hereafter referred to as Daily Tropospheric Excess – DTE) increases by up to a few ppm over regions affected by fires. A high positive correlation (R2~0.8) is found between annual DTE and CO2 emissions derived from burned area (Global Fire Emission Database – GFEDv2) across 10 regions with contrasted vegetation cover in southern Africa. Seasonal variability comparison between DTE and GFEDv2 also shows a good general agreement. Only two regions south of 10° S, show a seasonal increase of DTE starting earlier and rising up more rapidly than seen in two burned area products: GFEDv2 and L3JRC, the latter established by the Joint Research Center. The phase of the L3JRC dataset is however closer to DTE observations. This misfit could come from limitations in current burned area detection algorithms (difficulty in detecting small fires). 3-D simulations of the DTE signal by the LMDz General Circulation Model, in which a pyro-thermal plume model is activated, confirm the observations. A large fraction of fire products are directly injected in the mid-troposphere, well above the boundary layer. This rapid uplift of CO2, combined with atmospheric transport patterns in southern Africa during the dry season, characterized by a fluctuating continental gyre, produces a daily DTE signal mainly positive above the source region and either positive or negative outside of the source region. On a monthly mean, this results in a persistent DTE signal above the source region of an order of 1 ppm, while the impact of large-scale advection vanishes. We conclude that the DTE signal is a quantitative proxy of fire emission spatial patterns, in particular before the ATSR or MODIS observation periods when better quality fire count and burned area data became available, and can also bring a constraint in the analysis of their present results.
The impact of MM5 and WRF meteorology over complex terrain on CHIMERE model calculations

The objective of this study is to evaluate the impact of meteorological input data on calculated gas and aerosol concentrations. We use two different meteorological models (MM5 and WRF) together with the chemistry transport model CHIMERE. We focus on the Po valley area (Italy) for January and June 2005. Firstly we evaluate the meteorological parameters with observations. The analysis shows that the performance of both models in calculating surface parameters is similar, however differences are still observed. Secondly, we analyze the impact of using MM5 and WRF on calculated PM10 and O3 concentrations. In general CHIMERE/MM5 and CHIMERE/WRF underestimate the PMv concentrations for January. The difference in PM10 concentrations for January between CHIMERE/MM5 and CHIMERE/WRF is around a factor 1.6 (PM10 higher for CHIMERE/MM5). This difference and the larger underestimation in PM10 concentrations by CHIMERE/WRF are related to the differences in heat fluxes and the resulting PBL heights calculated by WRF. In general the PBL height by WRF meteorology is a factor 2.8 higher at noon in January than calculated by MM5. This study showed that the difference in microphysics scheme has an impact on the profile of cloud liquid water (CLW) calculated by the meteorological driver and therefore on the production of SO4 aerosol. A sensitivity analysis shows that changing the Noah Land Surface Model (LSM) in our WRF pre-processing for the 5-layer soil temperature model, calculated monthly mean PMv concentrations increase by 30%, due to the change in the heat fluxes and the resulting PBL heights. For June, PM10 calculated concentrations by CHIMERE/MM5 and CHIMERE/WRF are similar and agree with the observations. Calculated O3 values for June are in general overestimated by a factor 1.3 by CHIMERE/MM5 and CHIMERE/WRF. High temporal correlations are found between modeled and observed O3 concentrations.
Mexico City aerosol analysis during MILAGRO using high resolution aerosol mass spectrometry at the urban supersite (T0) – Part 1: Fine particle composition and organic source apportionment

Submicron aerosol was analyzed during the MILAGRO field campaign in March 2006 at the T0 urban supersite in Mexico City with a High-Resolution Time-of-Flight Aerosol Mass Spectrometer (HR-ToF-AMS) and complementary instrumentation. Mass concentrations, diurnal cycles, and size distributions of inorganic and organic species are similar to results from the CENICA supersite in April 2003 with organic aerosol (OA) comprising about half of the fine PM mass. Positive Matrix Factorization (PMF) analysis of the high resolution OA spectra identified three major components: chemically-reduced urban primary emissions (hydrocarbon-like OA, HOA), oxygenated OA (OOA, mostly secondary OA or SOA), and biomass burning OA (BBOA) that correlates with levoglucosan and acetonitrile. BBOA includes several very large plumes from regional fires and likely also some refuse burning. A fourth OA component is a small local nitrogen-containing reduced OA component (LOA) which accounts for 9% of the OA mass but one third of the organic nitrogen, likely as amines. OOA accounts for almost half of the OA on average, consistent with previous observations. OA apportionment results from PMF-AMS are compared to the PM2.5 chemical mass balance of organic molecular markers (CMB-OMM, from GC/MS analysis of filters). Results from both methods are overall consistent. Both assign the major components of OA to primary urban, biomass burning/woodsmoke, and secondary sources at similar magnitudes. The 2006 Mexico City emissions inventory underestimates the urban primary PM2.5 emissions by a factor of ~4, and it is ~16 times lower than afternoon concentrations when secondary species are included. Additionally, the forest fire contribution is at least an order-of-magnitude larger than in the inventory.
Source regions of some persistent organic pollutants measured in the atmosphere at Birkenes, Norway

A key feature of POPs (Persistent Organic Pollutants) is their potential for long-range atmospheric transport. In order to better understand and predict atmospheric source-receptor relationships of POPs, we have modified an existing Lagrangian transport model (FLEXPART) to include some of the key processes that control the atmospheric fate of POPs. We also present four years (2004–2007) of new atmospheric measurement data for polychlorinated biphenyls (PCBs) and hexachlorocyclohexanes (HCHs) obtained at Birkenes, an EMEP (European Monitoring and Evaluation Programme) site in southern Norway. The model overestimates measured PCB-28 and γ-HCH concentrations by factors of 2 and 8, respectively, which is most likely because the emissions used as input to the model are overestimated. FLEXPART captures the temporal variability in the measurements very well and, depending on season, explains 31–67% (14–62%) of the variance of measured PCB-28 (γ-HCH) concentrations. FLEXPART, run in a time-reversed (adjoint) mode, was used to identify the source regions responsible for the POP loading at the Birkenes station. Emissions in Central Europe and Eastern Europe contributed 32% and 24%, respectively, to PCB-28 at Birkenes, while Western Europe was found to be the dominant source (50%) for γ-HCH. Intercontinental transport from North America contributed 13% γ-HCH. While FLEXPART has no treatment of the partitioning of POPs between different surface media, it was found a very useful tool for studying atmospheric source-receptor relationships for POPs and POP-like chemicals that do not sorb strongly to atmospheric particles and whose atmospheric levels are believed to be mainly controlled by primary sources.