Abstract. Airborne measurements of trace gases and aerosol particles have been made in two aged biomass burning (BB) plumes over the East Atlantic (Gulf of Guinea). The plumes originated from BB in the Southern-Hemisphere African savanna belt. On the day of our measurements (13 August 2006), the plumes had ages of about 10 days and were respectively located in the middle troposphere (MT) at 3900–5500 m altitude and in the upper troposphere (UT) at 10 800–11 200 m. Probably, the MT plume was lifted by dry convection and the UT plume was lifted by wet convection. In the more polluted MT-plume, numerous measured trace species had markedly elevated abundances, particularly SO2 (up to 1400 pmol mol−1), HNO3 (5000–8000 pmol mol−1) and smoke particles with diameters larger than 270 nm (up to 2000 cm−3). Our MT-plume measurements indicate that SO2 released by BB had not experienced significant loss by deposition and cloud processes but rather had experienced OH-induced conversion to gas-phase sulfuric acid. By contrast, a significant fraction of the released NOy had experienced loss, most likely as HNO3 by deposition. In the UT-plume, loss of NOy and SO2 was more pronounced compared to the MT-plume, probably due to cloud processes. Building on our measurements and accompanying model simulations, we have investigated trace gas transformations in the ageing and diluting plumes and their role in smoke particle processing and activation. Emphasis was placed upon the formation of sulfuric acid and ammonium nitrate, and their influence on the activation potential of smoke particles. Our model simulations reveal that, after 13 August, the lower plume traveled across the Atlantic and descended to 1300 m and hereafter ascended again. During the travel across the Atlantic, the soluble mass fraction of smoke particles and their mean diameter increased sufficiently to allow the processed smoke particles to act as water vapor condensation nuclei already at very low water vapor supersaturations of only about 0.04%. Thereby, aged smoke particles had developed a potential to act as water vapor condensation nuclei in the formation of maritime clouds.
We studied wintertime aerosol formation and subsequent particle growth events that have been frequently observed in ambient air at a boreal forest site (SMEAR II station) in southern Finland. Aerosol size distributions, gas concentrations, biological activity and meteorological parameters have been measured at the site continuously since 1996. An important observation, based on flux measurements, was that all particle formation events were connected with either increased water evapo-transpiration or carbon dioxide uptake by the forest. However, increased H 2 O or CO 2 fluxes did also occur on days without aerosol formation events, but these occasions were connected to cloudy or polluted days with high pre-existing aerosol concentrations. Thus, our overall conclusion is that in order for an aerosol formation event to occur, some ecological or bio-geo-chemical activity is needed. During wintertime, this activity seems to be mostly related to snow-atmosphere interactions.
During the SCOUT-O3 tropical campaign in Darwin (Australia, November/December 2005) in situ measurements of SO2, NO, NOy and CO as well as CN measurements have been performed from the Falcon. A total of 23 transit and local flights have been carried out. Observed distributions and correlations of trace species for altitudes up to 12 km will be presented including median vertical profiles for the main SCOUT investigation area. Measurements of SO2 in the outflow of deep convection will be discussed in particular. In addition, a brief overview of the observations during the transit flights will be given.
Aircraft based measurements of tropospheric sulfur dioxide, SO2, have been carried out during four campaigns in South America (TROCCINOX), Australia (SCOUT-O3), Europe (INTEX/MEGAPLUME) and Africa (AMMA). SO2 has been measured by chemical ionization mass spectrometry (CIMS), permanently online calibrated with isotopically labelled SO2. The measurement method is described thoroughly in this work and the measured data are presented. Moreover, the data of the different regions are compared in general and typical air mass situations with SO2 enhancement are shown. A detailed analysis of four SO2 pollution plume cases emphasizes the main features: long-range transport, SO2 from metal smelters/volcanoes or from biomass burning. The SO2 measurements are analyzed in the light of simultaneously measured trace gas, particle and meteorological data. Air mass trajectory models (FLEXPART or HYSPLIT) are employed for a determination of the pollution origin. Further going evaluations with the aerosol model AEROFOR complete the analyses and point out, that the measured SO2 mole fractions are sufficient to explain new particle formation and growth. Finally, a first comparison of the measured SO2 to results from a global circulation model (ECHAM) with implemented sulfur chemistry showed a significant underestimation of the measured SO2 mole fraction by the model in the free troposphere.
Abstract. In this study we present measurements of selected trace gases and aerosols made in a boreal forest during the BACCI-QUEST IV intensive field campaign in Hyytiälä, Finland in April 2005. Springtime diel and vertical variations of VOCs are discussed in connection with the variations in other trace gases and with the prevailing meteorological conditions. A daytime and a nighttime event have been analysed in detail. The nighttime particle event occurred synchronously with huge increases in monoterpenes, while the second event type involved nucleation and was anti-correlated with sulphuric acid. Here we discuss the possible origins of these two distinct forms of aerosol production at the Hyytiälä site using the measurement data, air mass back trajectories and the optical stereoisomery of monoterpenes. Optical stereoisomery is used in source identification to distinguish between unnatural and natural monoterpene emissions.
Wahrend der SCOUT-Kampagne wurden die bisher umfangreichsten
modernen Messungen des atmospharischen Spurengases SO2 mit einem
neuen flugzeuggetragenen Ionen-Molekul-Reaktions-Massenspektrometer
durchgefuhrt. Wahrend der Transferfluge (Deutschland-Australien-
Deutschland) wurde permanent SO2 gemessen. In Nordaustralien wurden
mehrere lokale Messfluge durchgefuhrt. Alle Messungen wurden von einer
permanenten SO2-Eichung mit isotopisch markiertem SO2 begleitet.
Abstract. A large SO2-rich pollution plume of Chinese origin was detected by aircraft based CIMS (Chemical Ionization Mass Spectrometry) measurements at 3–7.5 km altitude over the North Atlantic on 3 May 2006 during the INTEX (Intercontinental Chemical Transport Experiment) campaign. Additional trace gases (NO, NOy, CO, H2O) were measured and used for comparison and source identification. All measurements took place aboard the German research aircraft Falcon. The atmospheric SO2 mole fraction was markedly increased inside the plume and reached up to 900 pmol/mol. The measured ratio SO2/NOy of 1.4 suggests combustion of coal or fuel with a very high sulfur content as a source of the excess SO2. Accompanying FLEXPART particle dispersion model simulations indicate that the probed pollution plume originated at low altitudes over densely populated and industrialized areas in eastern China about 8–12 days prior to the measurements.
Abstract. Atmospheric gaseous sulphuric acid was measured and its influence on particle formation and growth was investigated building on aerosol data. The measurements were part of the EU-project QUEST and took place at two different measurement sites in Northern and Central Europe (Hyytiälä, Finland, March-April 2003 and Heidelberg, Germany, March-April 2004). From a comprehensive data set including sulphuric acid, particle number size distributions and meteorological data, particle growth rates, particle formation rates and source rates of condensable vapors were inferred. Growth rates were determined in two different ways, from particle size distributions as well as from a so-called timeshift analysis. Moreover, correlations between sulphuric acid and particle number concentration between 3 and 6 nm were examined and the influence of air masses of different origin was investigated. Measured maximum concentrations of sulphuric acid were in the range from 1x106 to 16x106cm-3. The gaseous sulphuric acid lifetime with respect to condensation on aerosol particles ranged from 2 to 33min in Hyytiälä and from 0.5 to 8 min in Heidelberg. Most calculated values (growth rates, formation rates, vapor source rates) were considerably higher in Central Europe (Heidelberg), due to the more polluted air and higher preexistent aerosol concentrations. Close correlations between H2SO4 and nucleation mode particles (size range: 3-6 nm) were found on most days at both sites. The percentage contribution of sulphuric acid to particle growth was below 10% at both places and to initial growth below 20%. An air mass analysis indicated that at Heidelberg new particles were formed predominantly in air advected from southwesterly directions.
