Ultrafine particles (UFPs) are particulate matter of nanoscale size (less than 100 nanometres in diameter). Regulations do not exist for this size class of ambient air pollution particles, which are far smaller than the regulated PM10 and PM2.5 particle classes and are believed to have several more aggressive health implications than those classes of larger particulates. There are two main divisions that categorize types of UFPs. UFPs can either be carbon-based or metallic, and then can be further subdivided by their magnetic properties. Electron microscopy and special physical lab conditions allow scientists to observe UFP morphology. Airborne UFPs can be measured using a condensation particle counter, in which particles are mixed with alcohol vapor and then cooled allowing the vapor to condense around them which are then counted using a light scanner. UFPs are both manufactured and naturally occurring. UFPs are the main constituent of airborne particulate matter. Due to their numerous quantity and ability to penetrate deep within the lung, UFPs are a major concern for respiratory exposure and health.
Sources and applications
UFPs are both manufactured and naturally occurring. Hot volcanic lava, ocean spray, and smoke are common natural UFPs sources. UFPs can be intentionally fabricated as are fine particles to serve a vast range of applications in both medicine and technology. Other UFPs are byproducts, like emissions, from specific processes, combustion reactions, or equipment such as printer toner and automobile exhaust. In 2014, an air quality study found harmful ultrafine particles from the takeoffs and landings at Los Angeles International Airport to be of much greater magnitude than previously thought. There are a multitude of indoor sources that include but are not limited to laser printers, fax machines, photocopiers, the peeling of citrus fruits, cooking, tobacco smoke, penetration of contaminated outdoor air, chimney cracks and vacuum cleaners.
UFPs have a variety of applications in the medical and technology fields. They are used in diagnostic imagining, and novel drug delivery systems that include targeting the circulatory system, and or passage of the blood brain barrier to name just a few. Certain UFPs like silver based nanostructures have antimicrobial properties that are exploited in wound healing and internal instrumental coatings among other uses, in order to prevent infections. In the area of technology, carbon based UFPs have a plethora of applications in computers. This includes the use of graphene and carbon nanotubes in electronic as well as other computer and circuitry components. Some UFPs have characteristics similar to gas or liquid and are useful in powders or lubricants.
Exposure, risk, and health effects
The main exposure to UFPs is through inhalation. Due to their size, UFPs are considered to be respirable particles. Contrary to the behaviour of inhaled PM10 and PM2.5, ultrafine particles are deposited in the lungs, where they have the ability to penetrate tissue and undergo interstitialization, or to be absorbed directly into the bloodstream — and therefore are not easily removed from the body and may have immediate effect. Exposure to UFPs, even if components are not very toxic, may cause oxidative stress, inflammatory mediator release, and could induce heart disease, lung disease, and other systemic effects. 
There is a range of potential human exposures that include occupational, due to the direct manufacturing process or a byproduct from an industrial or office environment, as well as incidental,from contaminated outdoor air and other byproduct emissions. In order to quantify exposure and risk, both in vivo and in vitro studies of various UFP species are currently being done using a variety of animal models including mouse, rat, and fish. These studies aim to establish toxicological profiles necessary for risk assessment, risk management, and potential regulation and legislation.
Removal and mitigation
UFPs can be considered a persistent air pollutant. Mitigation and removal efforts are difficult due to the particle size. UFPs are captured on filters through a diffusion process. Significant reductions in indoor UFP particles are possible with proper filtration technologies, including HEPA rated filtration media, high effiency ASHRAE rated filtration media, and electrostatic filtration methods.  
Regulation and legislation
As the nanotechnology industry has grown, nanoparticles have brought UFPs more public and regulatory attention. UFP risk assessment research is still in the very early stages. There are continuing debates about whether to regulate UFPs and how to research and manage the health risks they may pose. As of March 19, 2008, the EPA does not yet regulate or research ultrafine particles, but has drafted a Nanomaterial Research Strategy, open for independent, external peer review beginning February 7, 2008 (Panel review on April 11, 2008). There is also debate about how the European Union (EU) should regulate UFPs.
- S. Iijima (1985). "Electron Microscopy of Small Particles". Journal of Electron Microscopy 34 (4): 249.
- V. Howard (2009). "Statement of Evidence: Particulate Emissions and Health (An Bord Plenala, on Proposed Ringaskiddy Waste-to-Energy Facility).". Retrieved 2011-04-26.
- J.D. Spengler (2000). Indoor Air Quality Handbook. ISBN 978-0-07-150175-0.
- T. Osunsanya et al. (2001). "Acute Respiratory Effects of Particles: Mass or Number?". Occupational Environmental Medecide 58: 154. doi:10.1136/oem.58.3.154.
- B. Collins (3 August 2007). "HP Hits Back in Printer Health Scare Row". PC Pro. Retrieved 2009-05-15.
- M. Benjamin (November 2007). "RT for Decision Makers in Respiratory Care". RT Magazine. Retrieved 2009-05-15.
- Weikel, Dan and Barboza, Tony (May 29, 2014) "Planes' exhaust could be harming communities up to 10 miles from LAX" Los Angeles Times
- S.M. Moghini et al. (2005). "Nanomedicine: Current Status and Future Prospects". The FASEB Journal 19 (3): 311–30. doi:10.1096/fj.04-2747rev. PMID 15746175.
- I. Chopra (2007). "The Increasing Use of Silver-Based Products As Antimicrobial Agents: A Useful Development or a Cause for Concern?". Journal of Antimicrobial Chemotherapy 59 (4): 587–90. doi:10.1093/jac/dkm006. PMID 17307768.
- "Nanotechnology: Ultrafine Particle Research". Environmental Protection Agency. 26 February 2008. Retrieved 2009-05-15.
- Int Panis, L, et al. (2010). "Exposure to particulate matter in traffic: A comparison of cyclists and car passengers". Atmospheric Environment 44: 2263–2270. doi:10.1016/j.atmosenv.2010.04.028.
- I. Romieu et al. (2008). "Air Pollution, Oxidative Stress and Dietary Supplementation: A Review". European Respiratory Journal 31 (1): 179–97. doi:10.1183/09031936.00128106. PMID 18166596.
- "AHA Scientific Statement: Particulate Matter Air Pollution and Cardiovascular Disease". Circulation 121. 2010. doi:10.1161/CIR.0b013e3181dbece1.
- J. Card et al. (2008). "Pulmonary Applications and Toxicity of Engineered Nanoparticles". American Journal of Physiology and Lung Cell Molecular Physiology 295 (3): L400. doi:10.1152/ajplung.00041.2008. PMC 2536798. PMID 18641236.
- L. Calderón-Garcidueñas et al. (2008). "Long-Term Air Pollution Exposure is Associated with Neuroinflammation, an Altered Innate Immune Response, Disruption of the Blood-Brain Barrier, Ultrafine Particulate Deposition, and Accumulation of Amyloid Β-42 and Α-Synuclein in Children and Young Adults". Toxicologic Pathology 36 (2): 289–310. doi:10.1177/0192623307313011. PMID 18349428.
- Jacobs, L (Oct 2010). "Subclinical responses in healthy cyclists briefly exposed to traffic-related air pollution". Environmental Health 9 (64). doi:10.1186/1476-069X-9-64. PMC 2984475. PMID 20973949.
- A. Seaton (2006). "Nanotechnology and the Occupational Physician". Occupational Medicine 56 (5): 312–6. doi:10.1093/occmed/kql049. PMID 16868129.
- I. Krivoshto; Richards, JR; Albertson, TE; Derlet, RW (2008). "The Toxicity of Diesel Exhaust: Implications for Primary Care". Journal of the American Board of Family Medicine 21 (1): 55–62. doi:10.3122/jabfm.2008.01.070139. PMID 18178703.
- C. Sayes et al. (2007). "Assessing Toxicity of Fine and Nanoparticles: Comparing in Vitro Measurements to in Vivo Pulmonary Toxicity Profiles". Toxicological Sciences 97 (1): 163–80. doi:10.1093/toxsci/kfm018. PMID 17301066.
- K. Dreher (2004). "Health and Environmental Impact of Nanotechnology: Toxicological Assessment of Manufactured Nanoparticles". Toxicological Sciences 77 (1): 3–5. doi:10.1093/toxsci/kfh041. PMID 14756123.
- A. Nel et al. (2006). "Toxic Potential of Materials at the Nanolevel". Science 311 (5761): 622–7. doi:10.1126/science.1114397. PMID 16456071.
- S.S. Nadadur et al. (2007). "The Complexities of Air Pollution Regulation: the Need for an Integrated Research and Regulatory Perspective". Toxicological Sciences 100 (2): 318–27. doi:10.1093/toxsci/kfm170. PMID 17609539.
- L.L. Bergoson (12 September 2007). "Greenpeace Releases Activists' Guide to REACH, Which Addresses Nanomaterials: Nanotech Law blog of Bergeson & Campbell, P.C.". Nanotechnology Law Blog. Bergeson & Campbell, P.C. Retrieved 2008-03-19.
- W.G. Kreyling, M. Semmler-Behnke, W. Möller (2006). "Ultrafine particle-lung interactions: does size matter?". Journal of Aerosol Medicine 19 (1): 74–83. doi:10.1089/jam.2006.19.74. PMID 16551218.
- M. Geiser et al. (2005). "Ultrafine Particles Cross Cellular Membranes by Nonphagocytic Mechanisms in Lungs and in Cultured Cells". Environmental Health Perspectives 113 (11): 1555–1560. doi:10.1289/ehp.8006. PMC 1310918. PMID 16263511.
- O. Günter et al. (2005). "Nanotoxicology: An Emerging Discipline Evolving from Studies of Ultrafine Particles". Environmental Health Perspectives 113: 823–839. doi:10.1289/ehp.7339. PMC 1257642. PMID 16002369.
- S. Radoslav et al. (2003). "Micellar Nanocontainers Distribute to Defined Cytoplasmic Organelles". Science 300 (5619): 615–618. doi:10.1126/science.1078192. PMID 12714738.
- "How Ultrafine Particles In Air Pollution May Cause Heart Disease". Science Daily. 22 January 2008. Retrieved 2009-05-15.
- K. Teichman (1 February 2008). "Notice of Availability of the Nanomaterial Research Strategy External Review Draft and Expert Peer Review Meeting". Federal Register 73 (30): 8309.[dead link]
- J.B. Skjaerseth, J. Wettestad (2 March 2007). "Is EU Enlargement Bad for Environmental Policy? Confronting Gloomy Expectations with Evidence". International Environmental Agreements. Fridtjof Nansen Institute. Retrieved 2008-03-19.