Journal of Exposure Science and Environmental Epidemiology (2011) 21, 20–30; doi:10.1038/jes.2009.59; published online 20 January 2010

Personal exposure to ultrafine particles

Lance Wallacea and Wayne Ottb

  1. aConsulting Scientist, Reston, Virginia, USA
  2. bDepartment of Civil and Environmental Engineering, Stanford University, Stanford, California, USA

Correspondence: Dr. Lance Wallace, Reston, Virginia, USA. Tel: +703 620 4543; Fax: +703 860 0678; E-mail:

Received 21 February 2009; Accepted 29 September 2009; Published online 20 January 2010.



Personal exposure to ultrafine particles (UFP) can occur while people are cooking, driving, smoking, operating small appliances such as hair dryers, or eating out in restaurants. These exposures can often be higher than outdoor concentrations. For 3 years, portable monitors were employed in homes, cars, and restaurants. More than 300 measurement periods in several homes were documented, along with 25h of driving two cars, and 22 visits to restaurants. Cooking on gas or electric stoves and electric toaster ovens was a major source of UFP, with peak personal exposures often exceeding 100,000 particles/cm3 and estimated emission rates in the neighborhood of 1012 particles/min. Other common sources of high UFP exposures were cigarettes, a vented gas clothes dryer, an air popcorn popper, candles, an electric mixer, a toaster, a hair dryer, a curling iron, and a steam iron. Relatively low indoor UFP emissions were noted for a fireplace, several space heaters, and a laser printer. Driving resulted in moderate exposures averaging about 30,000 particles/cm3 in each of two cars driven on 17 trips on major highways on the East and West Coasts. Most of the restaurants visited maintained consistently high levels of 50,000–200,000 particles/cm3 for the entire length of the meal. The indoor/outdoor ratios of size-resolved UFP were much lower than for PM2.5 or PM10, suggesting that outdoor UFP have difficulty in penetrating a home. This in turn implies that outdoor concentrations of UFP have only a moderate effect on personal exposures if indoor sources are present. A time-weighted scenario suggests that for typical suburban nonsmoker lifestyles, indoor sources provide about 47% and outdoor sources about 36% of total daily UFP exposure and in-vehicle exposures add the remainder (17%). However, the effect of one smoker in the home results in an overwhelming increase in the importance of indoor sources (77% of the total).


cooking; restaurants; gas stoves; electric stoves; vehicles; tobacco smoke