L. Lange

Transport of biomass burning smoke to the upper troposphere by deep convection in the equatorial region

During LBA-CLAIRE-98, we found atmospheric layers with aged biomass smoke at altitudes >10 km over Suriname. CO, CO2, acetonitrile, methyl chloride, hydrocarbons, NO, O3, and aerosols were strongly enhanced in these layers. We estimate that 80-95% of accumulation mode aerosols had been removed during convective transport. Trajectories show that the plumes originated from large fires near the Brazil/Venezuela border during March 1998. This smoke was entrained into deep convection over the northern Amazon, transported out over the Pacific, and then returned to South America by the circulation around a large upper-level anticyclone. Our observations provide evidence for the importance of deep convection in the equatorial region as a mechanism to transport large amounts of pyrogenic pollutants into the upper troposphere. The entrainment of biomass smoke into tropical convective clouds may have significant effects on cloud microphysics and climate dynamics.

Seasonal variations of a mixing layer in the lowermost stratosphere as identified by the CO‐O3 correlation from in situ measurements

[1]xa0Within the Stratosphere Troposphere Experiment by Aircraft Measurements (STREAM) project, airborne measurements of various trace species such as CO, CO2, N2O, and O3 have been performed in several years and seasons. Here we focus on a summer campaign conducted from Timmins (Canada, 47°N, 80°W) in July 1998 and winter measurements carried out in March 1997 from Kiruna (Sweden, 68°N, 20°E). From correlations between CO and O3 we identify a mixing layer in the lowermost stratosphere of which the vertical extent shows a significant seasonal variability. Troposphere to stratosphere exchange appears to be more vigorous in summer, although CO mixing ratios of the order of 15 ppbv indicate the presence of aged stratospheric air. While a significant tropospheric influence was observed up to potential temperatures of Θ = 330 K in March, the mixing layer in July increased to Θ = 360 K. In addition, its elevation above the tropopause also showed an increase. The CO-O3 correlation indicates that the higher elevation in July is most likely caused by a stronger contribution of subtropical tropospheric air, which was mixed into the lowermost stratosphere at the subtropical jet.

Saharan dust in Brazil and Suriname during the Large-Scale Biosphere-Atmosphere Experiment in Amazonia (LBA)- Cooperative LBA Regional Experiment (CLAIRE) in March 1998

Advection of Saharan dust was observed via chemical and optical measurements during March 1998 in Brazil and Suriname during the Large-Scale Biosphere-Atmosphere Experiment in Amazonia (LBA)-Cooperative LBA Airborne Regional Experiment (CLAIRE)-98 experiment. In Brazil the dust outbreak produced an increase of a factor of 3 in the daily mean mass concentration (up to 26±7 μg m−3) of particles smaller than 10 μm equivalent aerodynamic diameter (EAD), and in the daily mean aerosol particle scattering coefficient σs (up to 26±8 Mm−1 STP, ambient humidity). Background levels of aerosol scattering (ambient) were σs ∼ 10 Mm−1. The effect of dust advection was evident for all major crustal elements (Al, Si, Ca, Ti, Mn, and Fe), as well as the sea-salt elements (Na, Cl, and S), as the dust layer was transported at low altitude (below 800 hPa). Coarse P and organic carbon (OC) concentrations were not influenced by the occurrence of dust, and were mainly emitted by the rain forest. The dry scattering mass efficiency of dust (particles smaller than 10 μm EAD) was estimated to be between 0.65 (±0.06) and 0.89 (±0.08) m2 g−1. Airborne profiles of aerosol scattering showed two distinct types of vertical structure in the dust layer over Suriname, either vertically uniform (15, 26 March), or plume-like (25 March). Dust layers extended generally up to 700 hPa, while scattering layers occasionally encountered at higher altitudes resulted from smoke emitted by biomass burning in Venezuela and Colombia. Observations in South America were supported by measurements in Israel and Tenerife (Canary Islands), where the dust outbreaks were also detected.

Overview of the trace gas measurements on board the Citation aircraft during the intensive field phase of INDOEX

During the intensive field phase of the Indian Ocean Experiment (INDOEX), measurements of the atmospheric chemical and aerosol composition over the Indian Ocean were performed from a Cessna Citation aircraft. Measurements were performed during February and March 1999 over the northern Indian Ocean from 70 degreesE to 80 degreesE, and from 8 degreesN tb 8 degreesS in the 0-13 km altitude range. An overview of the trace gas-measurements is presented. In the lowest 3 km the highest levels of pollution were found during February 1999, mostly originating from northeastern India and southeastern Asia. Lower levels of pollution were detected in March 1999, when the sampled air mostly originated from the Arabian Sea region. The mixing ratios of a number of trace compounds, indicative of biomass burning, were well correlated. The pollutant emission factors inferred from the measurements are consistent with literature values for fire plumes, confirming that the residential use of biofuels in Asia is a major source of gaseous pollutants to the atmosphere over the Indian Ocean, in accord with emission databases. The removal of reactive trace gases was studied over an extended area without interfering local emissions, and is shown to be governed by photochemical processes rather than by mixing and deposition. At intermediate altitudes of 3-8 km the mixing ratios of all trace gases other than ozone were generally lower, and the measurements suggest that the Photochemical processing of these air masses is much more extensive than in the 0-3 kin range. In the 8-13 km altitude range some evidence is obtained for the importance of convective cloud systems in the transport of gaseous pollutants to the upper troposphere.

Detection of lightning-produced NO in the midlatitude upper troposphere during STREAM 1998

Simultaneous in situ measurements of NO, NOy, HNO3, CO, CO2, O-3, and aerosols were performed in the midlatitude upper troposphere (UT) and lower stratosphere during the Stratosphere-Troposphere Experiment by Aircraft Measurements (STREAM) 1998 summer campaign. The campaign focused on the region around Timmins in the Canadian province of Ontario (79.3 degreesW, 48.2 degreesN), close to the polar jet stream that rapidly transports trace species across the Atlantic Ocean. This paper focuses on the origin of total reactive nitrogen (NOy) in the UT, as our measurements show strong variations, which reflect large local sources. In situ production by lightning, stratospheric downdraft, aircraft emissions, and upward transport of polluted boundary layer air are discussed in two case studies as potential contributors. We use correlations among NO, NOy and CO to distinguish between transport from the boundary layer and in situ formations. Lightning production of NOx is found to be a strong contributor to the budget of NOy during high NOy episodes.

A novel tool for stable nitrogen isotope analysis in aqueous samples.

RATIONALEnBulk stable isotope analysis (BSIA) of dissolved matter (e.g. dissolved organic carbon, total nitrogen bound (TNb ), etc.) is of particular importance since this pool is a prime conduit in the cycling of N and C. Studying the two elemental pools is of importance, as transformation and transport processes of N and C are inextricably linked in all biologically mediated systems. No system able to analyze natural abundance stable carbon and nitrogen isotope composition in aqueous samples (without offline sample preparation) and simultaneously has been reported so far. Extension of the high-temperature combustion (HTC) system, to be capable of measuring TNb stable nitrogen isotope composition, is described in this study.nnnMETHODSnTo extend the TOC analyzer to be capable of measuring TNb , modifications from the HTC high-performance liquid chromatography/isotope ratio mass spectrometry (HPLC/IRMS) interface were implemented and expanded. A reduction reactor for conversion of NOx into N2 was implemented into the new developed system. The extension addresses mainly the development of the focusing unit for nitrogen and a degassing device for online separation of TNb from molecular nitrogen (N2 ) prior to injection.nnnRESULTSnThe proof of principle of the system was demonstrated with different compound solutions. In this initial testing, the δ15 NAIR-N2 values of the tested compounds were determined with precision and trueness of typically ≤0.5‰. Good results (uxa0≤xa00.5‰) could be achieved down to a TNb concentration of 40 mgN/L and acceptable results (uxa0≤xa01.0‰) down to 5 mgN/L. In addition, the development resulted in the first system reported to be suitable for simultaneous and direct δ13 C and δ15 N BSIA of aqueous samples.nnnCONCLUSIONSnThe development resulted in the first system shown to be suitable for both δ13 C and δ15 N direct BSIA in aqueous samples. This system could open up new possibilities in SIA-based research fields. Copyright