Abstract. The Model for Ozone and Related chemical Tracers, version 4 (MOZART-4) is an offline global chemical transport model particularly suited for studies of the troposphere. The updates of the model from its previous version MOZART-2 are described, including an expansion of the chemical mechanism to include more detailed hydrocarbon chemistry and bulk aerosols. Online calculations of a number of processes, such as dry deposition, emissions of isoprene and monoterpenes and photolysis frequencies, are now included. Results from an eight-year simulation (2000)(2001)(2002)(2003)(2004)(2005)(2006)(2007) are presented and evaluated. The MOZART-4 source code and standard input files are available for download from the NCAR Community Data Portal (http://cdp.ucar.edu).

We report measurements and analysis of a boreal forest fire, integrating the effects of greenhouse gases, aerosols, black carbon deposition on snow and sea ice, and postfire changes in surface albedo. The net effect of all agents was to increase radiative forcing during the first year (34 ± 31 Watts per square meter of burned area), but to decrease radiative forcing when averaged over an 80-year fire cycle (−2.3 ± 2.2 Watts per square meter) because multidecadal increases in surface albedo had a larger impact than fire-emitted greenhouse gases. This result implies that future increases in boreal fire may not accelerate climate warming.

Abstract. Measurements of aerosol composition were made with an Aerodyne High Resolution Time-of-Flight Aerosol Mass Spectrometer (HR-ToF-AMS) on board the NSF/NCAR C-130 aircraft as part of the Intercontinental Chemical Transport Experiment Phase B (INTEX-B) field campaign over the Eastern Pacific Ocean. The HR-ToF-AMS measurements of non-refractory submicron aerosol mass are shown to compare well with other aerosol instrumentation in the INTEX-B field study. Two case studies are described for pollution layers transported across the Pacific from the Asian continent, intercepted 3–4 days and 7–10 days downwind of Asia, respectively. Aerosol chemistry is shown to be a robust tracer for air masses originating in Asia, specifically the presence of sulfate dominated aerosol is a distinguishing feature of Asian pollution layers that have been transported to the Eastern Pacific. We examine the time scales of processing for sulfate and organic aerosol in the atmosphere and show that our observations confirm a conceptual model for transpacific transport from Asia proposed by Brock et al. (2004). Our observations of both sulfate and organic aerosol in aged Asian pollution layers are consistent with fast formation near the Asian continent, followed by washout during lofting and subsequent transformation during transport across the Pacific. Our observations are the first atmospheric measurements to indicate that although secondary organic aerosol (SOA) formation from pollution happens on the timescale of one day, the oxidation of organic aerosol continues at longer timescales in the atmosphere. Comparisons with chemical transport models of data from the entire campaign reveal an under-prediction of organic aerosol mass in the MOZART model, but much smaller discrepancies with the GEOS-Chem model than found in previous studies over the Western Pacific. No evidence is found to support a previous hypothesis for significant secondary organic aerosol formation in the free troposphere.

[1] We present a study of the sensitivity of isoprene emission calculations in a global chemistry transport model (CTM) to input land cover characteristics and analyze the impacts of changes in isoprene on the tropospheric budgets of atmospheric key species. The CTM Model for Ozone and Related Chemical Species, version 4 (MOZART-4) includes the online calculation of isoprene emissions based on the Model of Emissions of Gases and Aerosols from Nature (MEGAN), which is driven by three different land parameter inputs. We also included a tagging scheme in the CTM, which keeps track of the production of carbon containing species from isoprene oxidation. It is found that the amount of tropospheric carbon monoxide (CO), formaldehyde (HCHO) and peroxyacetylnitrate (PAN) explained by isoprene oxidation ranges from 9-16%, 15-27%, and 22-32%, depending on the isoprene emissions scenario. Changes in the global tropospheric burden with different land cover inputs can reach up to 10% for CO, 15% for HCHO, and 20% for PAN. Changes for ozone are small on a global scale, but regionally differences are as large as 3DU in the tropospheric column and as large as 5 ppbv in the surface concentrations. Our results demonstrate that a careful integration of isoprene emissions and chemistry in CTMs is very important for simulating the budgets of a number of atmospheric trace gases. We further demonstrate that the model tagging scheme has the capability of improving conventional methods of constraining isoprene emissions from space-borne HCHO column observations, especially in regions where a considerable part of the variability in the HCHO column is not related to isoprene.

[1] We present an inverse model analysis to quantify the emissions of wildfires in Alaska and Canada in the summer of 2004 using carbon monoxide (CO) data from the Measurements of Pollution in the Troposphere (MOPITT) remote sensing instrument together with the chemistry transport model MOZART (Model for Ozone and Related Chemical Tracers). We use data assimilation outside the region of the fires to optimally constrain the CO background level and the transport into that region. Inverse modeling is applied locally to quantify the fire emissions. Our a posteriori estimate of the wildfire emissions gives a total of 30 ± 5 Tg CO emitted during June-August 2004 which is of comparable order to the anthropogenic emissions for the continental US. The simulated CO fields have been evaluated by comparison with MOPITT and independent aircraft data. Citation: Pfister, G

h i g h l i g h t s Comprehensive review of studies of satellite data applied to emissions estimation. Overview of retrievals for eight major tropospheric air pollutants. Techniques to enhance the usefulness of satellite retrievals. Identification of target source categories for satellite data application. Recommendations on ways to improve the usability of satellite retrievals.

[1] Extensive wildfires burned in northern North America during summer 2004, releasing large amounts of trace gases and aerosols into the atmosphere. Emissions from these wildfires frequently impacted the PICO-NARE station, a mountaintop site situated 6-15 days downwind from the fires in the Azores Islands. To assess the impacts of the boreal wildfire emissions on the levels of aerosol black carbon (BC), nitrogen oxides and O 3 downwind from North America, we analyzed measurements of CO, BC, total reactive nitrogen oxides (NO y ), NO x (NO + NO 2 ) and O 3 made from June to September 2004 in combination with MOZART chemical transport model simulations. Long-range transport of boreal wildfire emissions resulted in large enhancements of CO, BC, NO y and NO x , with levels up to 250 ppbv, 665 ng m À3 , 1100 pptv and 135 pptv, respectively. Enhancement ratios relative to CO were variable in the plumes sampled, most likely because of variations in wildfire emissions and removal processes during transport. Analyses of DBC/DCO, DNO y /DCO and DNO x /DCO ratios indicate that NO y and BC were on average efficiently exported in these plumes and suggest that decomposition of PAN to NO x was a significant source of NO x . High levels of NO x suggest continuing formation of O 3 in these well-aged plumes. O 3 levels were also significantly enhanced in the plumes, reaching up to 75 ppbv. Analysis of DO 3 /DCO ratios showed distinct behaviors of O 3 in the plumes, which varied from significant to lower O 3 production. We identify several potential reasons for the complex effects of boreal wildfire emissions on O 3 and conclude that this behavior needs to be explored further in the future. These observations demonstrate that boreal wildfire emissions significantly contributed to the NO x and O 3 budgets in the central North Atlantic lower free troposphere during summer 2004 and imply large-scale impacts on direct radiative forcing of the atmosphere and on tropospheric NO x and O 3 .

Climate forecasts predict an increase in frequency and intensity of wildfires. Associations between health outcomes and population exposure to smoke from Washington 2012 wildfires were compared using surface monitors, chemical‐weather models, and a novel method blending three exposure information sources. The association between smoke particulate matter ≤2.5 μm in diameter (PM 2.5 ) and cardiopulmonary hospital admissions occurring in Washington from 1 July to 31 October 2012 was evaluated using a time‐stratified case‐crossover design. Hospital admissions aggregated by ZIP code were linked with population‐weighted daily average concentrations of smoke PM 2.5 estimated using three distinct methods: a simulation with the Weather Research and Forecasting with Chemistry (WRF‐Chem) model, a kriged interpolation of PM 2.5 measurements from surface monitors, and a geographically weighted ridge regression (GWR) that blended inputs from WRF‐Chem, satellite observations of aerosol optical depth, and kriged PM 2.5 . A 10 μg/m 3 increase in GWR smoke PM 2.5 was associated with an 8% increased risk in asthma‐related hospital admissions (odds ratio (OR): 1.076, 95% confidence interval (CI): 1.019–1.136); other smoke estimation methods yielded similar results. However, point estimates for chronic obstructive pulmonary disease (COPD) differed by smoke PM 2.5 exposure method: a 10 μg/m 3 increase using GWR was significantly associated with increased risk of COPD (OR: 1.084, 95%CI: 1.026–1.145) and not significant using WRF‐Chem (OR: 0.986, 95%CI: 0.931–1.045). The magnitude (OR) and uncertainty (95%CI) of associations between smoke PM 2.5 and hospital admissions were dependent on estimation method used and outcome evaluated. Choice of smoke exposure estimation method used can impact the overall conclusion of the study.