Effects of arctic sulphuric acid aerosols on wintertime low-level atmospheric ice crystals,humidity and temperature at Alert,Nunavut |
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| Institution: | 1. Centro Hospitalar Lisboa Norte EPE, Departamento do Tórax, Lisboa, Portugal;2. Departamento de Matemática, Universidade do Porto and Centro de Matemática da Universidade do Porto, Porto, Portugal;3. Unidade de Saúde Familiar, Saúde em Família, Agrupamento de Centros de Saúde do Grande Porto III, Maia/Valongo, Maia, Portugal;4. Centro Hospitalar Vila Nova de Gaia/Espinho EPE, Departamento de Saúde Ocupacional, Vila Nova de Gaia, Portugal;5. ISPUP-EPIUnit, Universidade do Porto, Porto, Portugal;6. Centro Hospitalar Vila Nova de Gaia/Espinho EPE, Departamento de Pneumologia, Vila Nova de Gaia, Portugal;7. Departamento de Ciências da Saúde Pública e Forenses e Educação Médica, Faculdade de Medicina, Universidade do Porto, Porto, Portugal;1. NASA Langley Research Center, MS 475, Hampton, VA 23681, United States;2. University of California at Los Angeles, Joint Institute for Regional Earth System Science and Engineering, 607 Charles E Young Drive East, Young Hall, Room 4242, Los Angeles 90095-7228, United States;3. Stevens Institute of Technology, 1 Castle Point on Hudson, Physics and Engineering Physics, Hoboken, NJ 07030, United States;4. NASA Goddard Space Flight Center, Code 613, Greenbelt, MD 20771, United States;1. Republic of Turkey Ministry of Transport, Maritime Affairs and Communications, General Directorate of Aeronautics and Space Technologies, Gazi Mustafa Kemal Blv. No. 128, 06100 Maltepe, Ankara, Turkey;2. Department of Electronic and Communication Engineering, Çankaya University, Eski?ehir Yolu, 29 km., 06810 Yenimahalle, Ankara, Turkey |
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| Abstract: | The effect of pollution-derived sulphuric acid aerosols on wintertime arctic lower atmospheric ice crystals is investigated. These anthropogenic aerosols differ from natural background aerosols by their number concentration, strong solubility and reduced homogeneous freezing temperature when internally mixed with other compounds. Furthermore, observations suggest that the ice-forming nuclei concentration is reduced by one to four orders of magnitude when the sulphuric acid aerosol concentration is high.Simulations performed using a column model and analysis of observed data for the period of 1991–1994 at Alert (82° 30'N, 62°20'W) are used to assess the changes of the boundary layer cloud characteristics by sulphuric acid aerosols and the potential effect on arctic climate. Results show that aerosol acidification leads to depletion of the ice crystal number concentration and an increase of its mean size. As a result, low-level precipitating ice crystals occur more frequently than ice fog and thick nonprecipitating clouds during high concentration of pollution-derived aerosols. This result is in agreement with observations that indicate an increase by more than 50% of the frequency of precipitating ice crystals when the weight proportion of sulphuric acid is greater than its mean value of 20% of the total aerosol mass. Consequently, the ice crystal size increases and number decreases, and the sedimentation flux of ice crystals and the dehydration rate of the lower troposphere are accelerated in the presence of high sulphuric acid aerosol concentration. As a result, the infrared radiation flux reaching the surface and the greenhouse effect are decreased. This process is referred to as the dehydration–greenhouse feedback. One-dimensional simulation for Alert during the period of 1991 to 1994 shows that a negative cloud radiative forcing of ?9 W m?2 may occur locally as a result of the enhanced dehydration rate produced by the aerosol acidity. |
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