Measurements of tracer and precursor gases of secondary photooxidants and aerosols in pollution plumes of major European and Asian population centers (MEPOLL)
Final Report Abstract
First detailed simultaneous measurements of formic acid (HCOOH) and sulfur dioxide (SO2) were performed in pollution plumes of major population centers in Europe and East Asia. Formic acid is one of the most abundant organic acids in the atmosphere, whereas SO2 is the precursor gas of sulfuric acid, a key inorganic acid in the atmosphere. Both gases have an important impact on aerosol and cloud formation and properties as well as acidity of precipitation. The HCOOH and SO2 data were sampled aboard the research aircraft HALO in the frame of the EMeRGe (Effect of Megacities on the transport and transformation of pollutants on the Regional to Global scales) project during two field campaigns based from Oberpfaffenhofen near Munich, Germany in July 2017 and Tainan, Taiwan in March 2018. For the EMeRGe measurements a Chemical Ionization Ion Trap Mass Spectrometer (CI-ITMS) were extended for the detection of HCOOH. Observations were performed in pollution plumes of the metropolitan areas of London (UK), Benelux (BE, NL), Ruhr (DE), Po-Valley, Rome (IT), Paris, Marseille (FR), and Barcelona (ES) in Europe, and Taichung, Taipei (Taiwan), Pearl River Delta, Yangtze River Delta (China), Manila (Republic of the Philippines), Seoul (Republic of Korea), Nagoya, Osaka, and Tokyo (Japan) in Asia. Connections between the source regions and the measured pollution plumes were established using air mass trajectory and emission dispersion calculations, as well as perfluorocarbon tracer experiments for selected cases. Emissions and pollution characteristics were investigated through analysis of emission ratios (ER), correlations between trace gases and aerosol properties, as well as the use of hydrocarbon tracer species to identify the influence of different emissions sources including benzene, acetonitrile, isoprene for anthropogenic, fire, and biogenic emissions, respectively. In general, the inferred ER of HCOOH/CO are observed to increase with plume age and range between 0.05 – 0.57 and 0.03 – 0.08 for plumes in Europe and Asia, respectively. The increases were found to be caused by secondary formation of HCOOH in the plumes. The inferred production rates amount to 18.5 pmol mol-1 HCOOH / nmol mol-1 CO / hour and 1.25 pmol mol-1 HCOOH / nmol mol-1 CO / hour in pollution plumes in Europe and Asia, respectively. The higher HCOOH secondary production rates in the European plumes are probably due to the higher isoprene emissions, an important HCOOH precursor gas, in the source regions in Europe during July conditions compared to the ones in Asia during March. The inferred ER of SO2/CO decrease with plume age due to oxidation of SO2 to H2SO4 (sulfuric acid) leading to formation and growth of sulfate aerosol. Inferred SO2-lifetimes amount to 10 - 15 hours and 32 - 45 hours in pollution plumes in Europe and Asia, respectively, in agreement with previous studies. The HCOOH and SO2 measurements in the pollution plumes are compared to model simulations using the chemistry-climate model MECO(n). The results of MECO(n) model runs for the EMeRGe measurements agree reasonable for SO2, however, largely underestimate the HCOOH volume mixing ratios observed in the pollution plumes. This is mainly due to an underestimation of the secondary formation of HCOOH in the plumes during transport by the MECO(n) model. The present measurements indicate the increasing importance of organic emissions, such as HCOOH, relative to the regulated classical emissions of SO2 for the properties of aerosols, clouds, and precipitation.
Publications
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Flugzeuggetragene Messungen von Ameisensäure und Schwefeldioxid in Emissionsfahnen urbaner Ballungsräume in Europa und Asien, Dissertation an der Fakultät für Physik der Ludwig-Maximilians-Universität München
Eirenschmalz, Lisa
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Overview: On the transport and transformation of pollutants in the outflow of major population centres – observational data from the EMeRGe European intensive operational period in summer 2017. Atmospheric Chemistry and Physics, 22(9), 5877-5924.
Andrés Hernández, M. Dolores; Hilboll, Andreas; Ziereis, Helmut; Förster, Eric; Krüger, Ovid O.; Kaiser, Katharina; Schneider, Johannes; Barnaba, Francesca; Vrekoussis, Mihalis; Schmidt, Jörg; Huntrieser, Heidi; Blechschmidt, Anne-Marlene; George, Midhun; Nenakhov, Vladyslav; Harlass, Theresa; Holanda, Bruna A.; Wolf, Jennifer; Eirenschmalz, Lisa; Krebsbach, Marc; ... & Burrows, John P.
