Environmentally Conscious Design & Manufacturing

1. Environmentally Conscious Design & Manufacturing Class10: Air Quality 1 Prof. S. M. Pandit

2. Agenda • Air quality and manufacturing • Definitions • Standards set by EPA • Aerosols • Impact on health • Particle motion ? • Removal

3. Air Quality and Manufacturing Integrated View Product {Quality, Economics} Manufacturing Material, Energy Environment {Solid / Liquid / Aerosols / Gases / Energy} Wastes (Material / Energy) Product

4. Air Quality and Manufacturing • EPA regulations in Manufacturing - Health • Need for revision of 25 year old standards Particulate matter exposures to particles smaller than those that were being regulated by EPA - lodge deeply in the lungs and - cause premature deaths and respiratory problems

5. Air Quality and Manufacturing Aerosols / Dust settling inside Aerosols and Dust Aerosols / Dust to Environment Process 1 .. n Manufacturing Facility

6. Aerosols - Definitions • Aerosols: Suspensions of solid or liquid particles in a gas (usually air). • The particulate portion of an aerosol is referred to as Particulate Matter or PM. • Particulate Matter is a generic term applied to chemically heterogeneous discrete liquid droplets or solid particles. • The metric used for describing PM is the micron, or micrometer. • The PM in an aerosol can range in size from 0.001 to greater than 100 microns in diameter.

7. Aerosols - Definitions • Particulates are generally categorized based on size: • Coarse Particles are larger than 2 microns in diameter • Fine Particles are between 0.1 and 2 microns in diameter • Ultrafine Particles are less than 0.1 micron • Most aerosol particles are polydisperse -- they have a wide range of particle sizes that must be characterized by statistical measures. In some cases, such as with an ink jet printer, it is desirable to have a monodisperse aerosol with particles of equal size.

8. Aerosol Terminology • Solid-Particle Aerosols: • Dust: formed by mechanical disintegration of a parent material -- size range from submicron to visible • Fume: produced by condensation of vapors or gaseous combustion products -- less than 1 micron

9. Aerosol Terminology • Liquid-Droplet Aerosols: • Mist: formed by condensation or atomization -- size range from submicron to 20 microns • Fog: visible mist (high particle concentration)

10. Aerosol Terminology • Solid/Liquid particle aerosols: • Smoke: visible aerosol resulting from incomplete combustion -- less than 1 micron • Smog: photochemical reaction products, usually combined with water vapor -- less than 2 microns

11. EPA Standards - Revision • Primary (health-based) PM standards revision • New annual PM2.5 standard set at 15 micrograms per cubic meter (µg/m3) and • New 24-hour PM2.5 standard set at 65 µg/m3. • EPA is retaining the current annual PM10 standard of 50 µg/m3 and adjusting the PM10 24-hour standard of 150 µg/m3 by changing the form of the standard.

12. EPA Standards - Revision Micrograms / cubic meter

13. EPA Standards - Revision • EPA is revising the secondary (welfare-based) standards • - Identical to the primary standards. • PM2.5 and PM10 standards, combined with the Clean Air Act-required regional haze program, will provide • Protection against the major PM-related welfare effects • Visibility impairment • Soiling and • Materials damage.

14. Health Effects - 1 What are the PM Effects of Concern? The characteristics, sources, and potential health effects of larger or "coarse" fraction particles (from 2.5 to 10 micrometers in diameter) and smaller or "fine” particles (smaller than 2.5 micrometers in diameter) are very different. Coarse particles come from sources such as windblown dust from the desert or agricultural fields and dust kicked up on unpaved roads by vehicle traffic.

15. Health Effects - 2 Fine particles are generally emitted from activities such as industrial and residential combustion and from vehicle exhaust. Fine particles are also formed in the atmosphere when gases such as sulfur dioxide, nitrogen oxides, and volatile organic compounds, emitted by combustion activities, are transformed by chemical reactions in the air.

16. Health Effects - 3 Coarse particles - Accumulate in the respiratory system and aggravate health problems such as asthma. Fine particles - Penetrate deeply into the lungs, are more likely than coarse particles to contribute to the health effects (e.g., premature mortality and hospital admissions)

17. Health Effects - 4 These recent community studies find that adverse public health effects are associated with exposure to particles at levels well below the previous PM standards for both short-term (from less than 1 day to up to 5 days) and long-term (from generally a year to several years) periods.

18. Health Effects - 5 • Premature death • Increased hospital admissions and emergency room visits (primarily the elderly and individuals with cardiopulmonary disease) • Increased respiratory symptoms and disease (children and individuals with cardiopulmonary disease such as asthma)

19. Health Effects - 6 • Decreased lung function • (particularly in children • and individuals with asthma); and • Alterations in • - Lung tissue and structure • and in • - Respiratory tract defense mechanisms.

20. Motion? • The forces acting on an aerosol particle in still air are: • Gravitational Force, W • Bouyancy Force • Drag Force

21. Motion ? Bouyancy Force According to Archimedes' Bouyancy Principle, the bouyant force exerted on a floating body is equal to the weight of the fluid displaced by the body. The Bouyancy Force exerted on a spherical particle is: where r is the gas density.

22. Motion ? Drag Force Sir Isaac Newton derived the general equation for the resistance force on a spheremoving through a gas while investigating the ballistics of cannon balls. Newton theorized that a sphere must push aside a volume of gas equal to the projected area of the sphere times its velocity. The general form of Newton's resistance equation is:

23. Motion ? Drag Coefficient The coefficient of drag, ,is dependent upon Reynold's number (Re). For flow around a sphere, there are three regions for the drag coefficient: the Stoke's Law region, the Transition region, and Newton's Law region.

24. Motion ? • Settling velocity of particles

25. Removal Aerosol Particle Deposition Mechanisms There is a general misconception about how air filters work, i.e., that they work like a microscopic sieve. Particles are simply trapped due to its large size relative to the sieve. This is not the case for most types of air filters. Instead, aerosols are captured via collision and attachment to fiber surface.

26. Removal • There are five mechanisms by which an aerosol particle can be deposited on a fiber: • Interception • Inertia impaction • Diffusion • Sedimentation • Electrostatic attraction

27. Removal Interception Interception occurs when particles do not depart from the streamlines. The inertia or Brownian motion of particles is negligible. Particles following streamlines arrive at the fibers and get "intercepted" on the fiber surface.

28. Removal Inertia Impaction This occurs when particles cannot adjust to the "sudden" change of streamlines near fibers, and, due to inertia, depart from the streamlines and impact on the fiber surface.

29. Removal Diffusion Diffusion occurs when smaller particles having Brownian motion hit the surface of the fibers. Flow is dictated by the concentration gradient