Abstract. An airfreight container with automated

[1] We investigated trace gas emissions from a biomass fire near Otavi, northern Namibia, on 13 September 2000 as part of the Southern African Regional Science Initiative 2000 (SAFARI 2000). Observations included fast measurements of carbon monoxide (CO), ozone (O 3 ), acetone (propanone, CH 3 COCH 3 ), and acetonitrile (ethanenitrile or methyl cyanide, CH 3 CN). Additionally, flask samples were taken and analyzed for nonmethane hydrocarbons (NMHCs). Measurements close to the fire were used to quantify the emissions of the different compounds. Several transects were flown through the plume downwind to study the chemical changes in the plume during the first 2 hours after the emission. Fast production of O 3 was observed, with the O 3 /CO molar enhancement ratio ER(O 3 /CO) reaching $0.10 in the plume after 2 hours. Acetone molar enhancement ratios (ER(acetone/CO) were $5 Â 10 À3 in the very young plume but $9 Â 10 À3 after 1-2 hours of aging, pointing to a substantial fast secondary acetone formation. To understand the chemical processes occurring in the plume, we simulated the plume chemistry with a dilution box model. The fast O 3 production is well reproduced, whereas acetone mixing ratios in the aging plume are underestimated by the model. This points to additional yet unidentified acetone precursors. The model suggests an overall molar enhancement ratio of these compounds with respect to CO of 7.5 Â 10 À3 and a reaction rate coefficient of 6 Â 10 À11 cm 3 s À1 for the reaction with HO radicals. The secondary acetone production may cause the net acetone source from biomass burning to be underestimated when only data from observations immediately near the fires are considered. The atmospheric implications of these findings are discussed.

Abstract. A large airfreight container with automated instruments for measurement of atmospheric gases and trace compounds was operated on a monthly basis onboard a Boeing 767-300 ER of LTU International Airways during long-distance flights from 1997 to 2002 (CARIBIC, Civil Aircraft for Regular Investigation of the Atmosphere Based on an Instrument Container, http://www.caribic-atmospheric.com). Subsequently a more advanced system has been developed, using a larger capacity container with additional equipment and an improved inlet system. CARIBIC phase #2 was implemented on a new long-range aircraft type Airbus A340-600 of the Lufthansa German Airlines (Star Alliance) in December 2004, creating a powerful flying observatory. The instrument package comprises detectors for the measurement of O3, total and gaseous H2O, NO and NOy, CO, CO2, O2, Hg, and number concentrations of sub-micrometer particles (>4 nm, >12 nm, and >18 nm diameter). Furthermore, an optical particle counter and a proton transfer mass spectrometer (PTR-MS) are installed. Aerosol samples are collected for analyses of elemental composition and particle morphology after flight. Air samples are taken in glass containers for laboratory analyses of hydrocarbons, halocarbons and greenhouse gases in several laboratories. Absorption tubes collect oxygenated volatile organic compounds. Three differential optical absorption spectrometers (DOAS) with their telescopes mounted in the inlet system measure atmospheric trace gases such as BrO, HONO, and NO2. A video camera mounted in the inlet provides information about clouds along the flight track. Here we describe the flying observatory and report examples of measurement results.

[1] Chemical, physical, and optical measurements of aerosol particle properties within an aged biomass-burning plume were performed on board a research aircraft during a profile descent over a ground-based site in northeastern Greece (40°24 0 N, 23°57 0 E; 170 m asl) where continuous measurements of the spectral downwelling solar irradiance (global, direct, and diffuse) are being made. The aerosol optical depth measured at the ground during the time of overflight was significantly enhanced (0.39 at a wavelength of 500 nm) due to a haze layer between 1 and 3.5 km altitude. The dry particle scattering coefficient within the layer was around 80 Mm À1 , and the particle absorption coefficient was around 15 Mm À1 , giving a single scattering albedo of 0.89 at 500 nm (dry state). The black carbon fraction is estimated to account for 6-9% of the total accumulation mode particle mass (<1 mm diameter). The increase of the particle scattering coefficient with increasing relative humidity at 500 nm is of the order of 40% for a change in relative humidity from 30 to 80%. The dry, altitude-dependent, particle number size distribution is used as input parameter for radiative transfer calculations of the spectral short-wave, downwelling irradiance at the surface. The agreement between the calculated irradiances and the experimental results from the ground-based radiometer is within 10%, both for the direct and the diffuse components (at 415, 501, and 615 nm). Calculations of the net radiative forcing at the surface and at the top of the atmosphere (TOA) show that due to particle absorption the effect of aerosols is much stronger at the surface than at the TOA. Over sea the net short-wave radiative forcing (daytime average) between 280 nm and 4 mm is up to À64 W m À2 at the surface and up to À22 W m À2 at the TOA.

[1] We performed airborne measurements of sulfur dioxide (SO 2 ), carbon monoxide (CO), and aerosol chemical/microphysical properties over the Aegean Sea. The data were collected on board the Met Office C-130 research aircraft in August 1998. High SO 2 mixing ratios up to 18 ppb and aerosol sulfate levels up to 500 ppt were measured near Thessaloniki in northern Greece. The highest concentrations were observed at altitudes between 1 and 2 km, while near the surface much lower SO 2 mixing ratios between 1 and 4 ppb were found. The pollution was transported southward over the Aegean Sea as far south as Crete, where SO 2 mixing ratios up to 5 ppb were observed. The combined results of the SO 2 , aerosol sulfate, and particle size distribution measurements indicate air masses containing emissions with different ages, which range from a few hours to several days. Fossil fuel pollution observed over northern Greece is transported from eastern Europe (Bulgaria, Romania, and Turkey). Additionally, our measurements indicate significant contributions from forest fires, in particular from haze layers that originated ten days earlier from fires over the Northwestern Canadian territories, and had crossed the Atlantic and passed over Europe. CO layers 1 to 2 km deep were observed above 1 km. Often a double-layer structure with a secondary CO layer above 3.5 km was also observed. We estimate that the contribution of biomass burning to the CO measured over Greece is fourfold that of fossil fuel. The lower layer had a significant number of particles in the accumulation mode (N p , size range 0.1-1 mm, ratio N p /CO of the order of 2-6 cm À3 (STP) ppb À1 ), while the upper layers were particle-depleted by convection and wet scavenging. The Aitken particle mode (size range 5-100 nm) was depleted both in the lower and in the upper layers. This suggests that the Aitken particles originally present in the lower layers had already grown to the accumulation mode size when detected.

On the other hand, high mixing ratios of sulfur dioxide (up to 1.5 ppb) and aerosol sulfate (up to 3 ppb) indicate the influence of fossil fuel burning. During most flights the contributions from these two sources were well mixed within the same air mass, suggesting that the sources on the ground are also close to each other. This is consistent with the assumption that biomass is mainly burnt as biofuel for domestic use in populated areas, where fossil fuel is also used. The ratios dX/dCO (X:acetone, acetonitrile, sulfur dioxide, potassium, or sulfate) measured during the flights indicate that most of the CO in the continental outflow is due to biomass or biofuel burning, whereas the majority of the aerosols results from fossil fuel burning.

[1] Mass-spectrometric measurements of acetone (CH 3 COCH 3 ) have been performed monthly using a Lufthansa Airbus A340-600 passenger aircraft between February 2006 and December 2008. In total, 106 measurement flights (4 per month) were conducted between Germany and South America, North America, South Asia, and East Asia. Here measurements collected between 33°N and 56°N in the upper troposphere (UT) and lowermost stratosphere (LMS) at 9-12 km altitude are analyzed. By integrating data collected at 12 ozonesonde stations, ozone concentrations measured on flight are translated into a representative (mixing-based) altitude above the thermal tropopause. A strong seasonal variation of acetone occurs at the midlatitude tropopause with maxima of ∼900 parts per 10 12 vol (pptv) in summer and minima of ∼200 pptv in midwinter. This seasonality propagates into the LMS in approximately 6 weeks with rapidly decreasing concentrations and increasing phase shifts reaching 2 km above the tropopause. Throughout the year, acetone and ozone are highly negatively correlated in the LMS with a mean linear correlation coefficient (R) of −0.93. This linear relationship marks the O 3 -acetone-based extratropical tropopause mixing layer (exTL). A "stratospheric intrusion height of acetone" (Z acetone ) is defined that concurs with the vertical depth of the O 3 -CO-based exTL, namely, averaging ∼2.2 km but with slightly lower values in winter. Probability density functions (PDFs) and the course of the seasonal variation of acetone relative to the tropopause are interpreted regarding the in-mixing and subsequent dispersion of acetone in the LMS.Citation: Sprung, D., and A. Zahn (2010), Acetone in the upper troposphere/lowermost stratosphere measured by the CARIBIC passenger aircraft: Distribution, seasonal cycle, and variability,

Abstract. Total gaseous mercury (TGM) was measured onboard a passenger aircraft during monthly CARIBIC flights (Civil Aircraft for Regular Investigation of the Atmosphere Based on an Instrumented Container) made between May 2005 and March 2007 on the routes Frankfurt-São Paulo-Santiago de Chile and back (seven times four flights) and Frankfurt-Guangzhou-Manila and back (twelve times four flights). The data provide for the first time an insight into the seasonal distributions of TGM in the upper troposphere and lower stratosphere (UT/LS) of both hemispheres and demonstrate the importance of mercury emissions from biomass burning in the Southern Hemisphere. Numerous plumes were observed in the upper troposphere, the larger of which could be characterized in terms of Hg/CO emission ratios and their probable origins. During the flights to China TGM correlated with CO in the upper troposphere with a seasonally dependent slope reflecting the longer lifetime of elemental mercury when compared to that of CO. A pronounced depletion of TGM was always observed in the extratropical lowermost stratosphere. TGM concentrations there were found to decrease with the increasing concentrations of particles. Combined with the large concentrations of particle bond mercury in the stratosphere observed by others, this finding suggests either a direct conversion of TGM to particle bound mercury or an indirect conversion via a semivolatile bivalent mercury compound. Based on concurrent measurements of SF6 during two flights, the rate of this conversion is estimated to 0.4 ng m−3 yr−1. A zero TGM concentration was not observed during some 200 flight hours in the lowermost stratosphere suggesting an equilibrium between the gaseous and particulate mercury.