We present a comprehensive description and benchmark evaluation of the tropospheric chemistry version of the global chemistry transport model TM5 (Tracer Model 5, version TM5-chem-v3.0). A full description is given concerning the photochemical mechanism, the interaction with aerosol, the treatment of the stratosphere, the wet and dry deposition parameterizations, and the applied emissions. We evaluate the model against a suite of ground-based, satellite, and aircraft measurements of components critical for understanding global photochemistry for the year 2006. <br><br> The model exhibits a realistic oxidative capacity at a global scale. The methane lifetime is ~8.9 years with an associated lifetime of methyl chloroform of 5.86 years, which is similar to that derived using an optimized hydroxyl radical field. <br><br> The seasonal cycle in observed carbon monoxide (CO) is well simulated at different regions across the globe. In the Northern Hemisphere CO concentrations are underestimated by about 20 ppbv in spring and 10 ppbv in summer, which is related to missing chemistry and underestimated emissions from higher hydrocarbons, as well as to uncertainties in the seasonal variation of CO emissions. The model also captures the spatial and seasonal variation in formaldehyde tropospheric columns as observed by SCIAMACHY. Positive model biases over the Amazon and eastern United States point to uncertainties in the isoprene emissions as well as its chemical breakdown. <br><br> Simulated tropospheric nitrogen dioxide columns correspond well to observations from the Ozone Monitoring Instrument in terms of its seasonal and spatial variability (with a global spatial correlation coefficient of 0.89), but TM5 fields are lower by 25–40%. This is consistent with earlier studies pointing to a high bias of 0–30% in the OMI retrievals, but uncertainties in the emission inventories have probably also contributed to the discrepancy. <br><br> TM5 tropospheric nitrogen dioxide profiles are in good agreement (within ~0.1 ppbv) with in situ aircraft observations from the INTEX-B campaign over (the Gulf of) Mexico. <br><br> The model reproduces the spatial and seasonal variation in background surface ozone concentrations and tropospheric ozone profiles from the World Ozone and Ultraviolet Radiation Data Centre to within 10 ppbv, but at several tropical stations the model tends to underestimate ozone in the free troposphere. <br><br> The presented model results benchmark the TM5 tropospheric chemistry version, which is currently in use in several international cooperation activities, and upon which future model improvements will take place

[1] Multiwavelength backscatter and extinction profiling was performed with a unique aerosol Raman lidar at Hulhule (4°N, 73°E), Maldives, as part of the Indian Ocean Experiment (INDOEX) between February 1999 and March 2000. The Raman lidar allowed a direct determination of the volume extinction coefficient of the particles at 355 and 532 nm at ambient conditions. Heavily polluted air masses from the Asian continent passed over the Maldives during the northeast monsoon seasons. The mean 532-nm particle optical depth was about 0.3; maximum values of 0.7 were measured. Above the polluted marine boundary layer, lofted plumes were found up to 4000-m height. On average, the freetropospheric aerosol layers contributed 30-60% to the particle optical depth. The volume extinction coefficient at 532 nm typically ranged from 25 to 175 Mm À1 in the elevated layers. The pollution plumes are characterized separately for the air masses from Southeast Asia, North India, and South India. The analysis includes backward trajectories and emission inventory data for India. The extinction-to-backscatter ratio (lidar ratio) at 532 nm was mostly between 30 and 100 sr, and accumulated at 50-80 sr for highly absorbing particles from northern India. The shift of the lidar-ratio distribution for northern Indian aerosols by about 20 sr toward larger values compared to European values is consistent with an aerosol black-carbon content of up to 20%. The Å ngström exponent (for short wavelengths 355/400/532 nm) ranged mostly from 1 to 1.6 for Southeast Asian particles, from 0.8 to 1.4 for North Indian pollution, and from 0.6 to 1 for South Indian air masses. The comparably low Indian Å ngström exponents (indicating a comparably large mean particle radius) are possibly caused by the high contribution of biomass combustion to the aerosol formation in India. Results of a correlation analysis based on the lidar ratio, extinction coefficient, Å ngström exponents, and relative humidity are presented. In most cases only a weak relationship or no relationship was found between the different parameters.

Abstract. The change in aerosol properties during the transition from the more polluted spring to the clean summer in the Arctic troposphere was studied. A six-year data set of observations from Ny-Ålesund on Svalbard, covering the months April through June, serve as the basis for the characterisation of this time period. In addition four-day-back trajectories were used to describe air mass histories. The observed transition in aerosol properties from an accumulationmode dominated distribution to an Aitken-mode dominated distribution is discussed with respect to long-range transport and influences from natural and anthropogenic sources of aerosols and pertinent trace gases. Our study shows that the air-mass transport is an important factor modulating the physical and chemical properties observed. However, the airmass transport cannot alone explain the annually repeated systematic and rather rapid change in aerosol properties, occurring within a limited time window of approximately 10 days. With a simplified phenomenological model, which delivers the nucleation potential for new-particle formation, we suggest that the rapid shift in aerosol microphysical properties between the Arctic spring and summer is mainly driven by the incoming solar radiation in concert with transport of precursor gases and changes in condensational sink.

Abstract.Airborne measurements of the aerosol number concentration and size distribution were conducted over the northern Indian Ocean during the Indian Ocean Experiment (INDOEX) in February-March 1999. Vertical profiles of the aerosol number concentration demonstrate elevated concentrations of nucleation mode particles in a layer between 8 and 12.5 km altitude. By using a novel combination of back trajectory information and cloud top temperatures retrieved from satellite images, it is shown that these particles most likely originated from the outflow of large convective clouds. Accumulation mode particles observed at these altitudes show indications for cloud processing. The aerosol size distributions observed in the layer between 4 and 8 km altitude show characteristics of an aged aerosol. In this layer the accumulation mode particle number concentration presents a minimum, a low variability, and very few particles larger than 0.7/xm diameter. The aerosol in the marine boundary layer can be characterized by high number concentrations of submicron and accumulation mode particles, which gradually decrease with distance from the Indian subcontinent. The particle loss rate is equivalent to 10-16 cm -3 per hour. This decrease takes place over the whole size distribution and can therefore not be explained by coagulation, but is likely due to precipitation and entrainment of free tropospheric air.

[1] We present a regional and seasonal climatology of SHADOZ ozone profiles in the troposphere and tropical tropopause layer (TTL) based on measurements taken during the first five years of Aura, 2005Aura, -2009, when new stations joined the network at Hanoi, Vietnam; Hilo, Hawaii; Alajuela/Heredia, Costa Rica; Cotonou, Benin. In all, 15 stations operated during that period. A west-to-east progression of decreasing convective influence and increasing pollution leads to distinct tropospheric ozone profiles in three regions: (1) western Pacific/eastern Indian Ocean; (2) equatorial Americas (San Cristóbal, Alajuela, Paramaribo); (3) Atlantic and Africa. Comparisons in total ozone column from soundings, the Ozone Monitoring Instrument (OMI, on Aura, 2004-) satellite and ground-based instrumentation are presented. Most stations show better agreement with OMI than they did for EP/TOMS comparisons (1998)(1999)(2000)(2001)(2002)(2003)(2004); Earth-Probe/Total Ozone Mapping Spectrometer), partly due to a revised above-burst ozone climatology. Possible station biases in the stratospheric segment of the ozone measurement noted in the first 7 years of SHADOZ ozone profiles are re-examined. High stratospheric bias observed during the TOMS period appears to persist at one station. Comparisons of SHADOZ tropospheric ozone and the daily Trajectory-enhanced Tropospheric Ozone Residual (TTOR) product (based on OMI/MLS) show that the satellite-derived column amount averages 25% low. Correlations between TTOR and the SHADOZ sondes are quite good (typical r 2 = 0.5-0.8), however, which may account for why some published residual-based OMI products capture tropospheric interannual variability fairly realistically. On the other hand, no clear explanations emerge for why TTOR-sonde discrepancies vary over a wide range at most SHADOZ sites.