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Understanding the Atmospheric Residence Time of PM2.5 for Environmental Planning

Learn about the impact of PM2.5 transport on air quality with insights into residence time, spatial scales, and transport distances. Discover how height affects residence time and the range of transport for better environmental decision-making.

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Understanding the Atmospheric Residence Time of PM2.5 for Environmental Planning

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  1. Atmospheric Lifetime and the Range of PM2.5 Transport Background and Rationale Atmospheric Residence Time and Spatial Scales Residence Time Dependence on Height Range of Transport Resource Links Contact: Rudolf Husar, rhusar@mecf.wustl.edu

  2. Background and Rationale • Residence time refers to the time span between the PM emission (or the emission of their precursor gases) and its removal from the atmosphere. • Residence time determines the range of impact of a specific sources.

  3. Atmospheric Residence Time and Spatial Scales • PM2.5 sulfates reside 3-5 days in the atmosphere • Ultrafine 0.1 m coagulate while coarse particles above 10 m settle out more rapidly. • PM in the 0.1-1.0 m size range has the longest residence time because they neither settle, nor coagulate. • Atmospheric residence time and transport distance are related by the average wind speed, say 5 m/s. • Residence time of several days yields ‘long range transport’ and more uniform spatial pattern. • On the average, PM2.5 particles are transported 1000 or more km from the source of their precursor gases.

  4. Residence Time Dependence on Height. • The PM2.5 residence time increased with height. • Within the atmospheric boundary layer (the lowest 1-2 km), the residence time is 3-5 days. • If aerosols are lifted to 1-10 km in the troposphere, they are transported for weeks and many thousand miles before removal. • The lifting of boundary layer air into the free troposphere occurs by deep convective clouds and by converging airmasses near weather fronts.

  5. Range of Transport • The residence time determines the range of transport. For example, given a residence time of 4 days (~100 hrs) and a mean transport speed of 10 mph, the transport distance is about 1000 miles. • The range of transport determines the ‘region of influence’ of specific sources.

  6. Resource Links • Workbook Table of Contents • Comment and Feedback Page • Applications / Reports • Data sets used in the Applications • Methods and tools used in the Applications

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