title: How long does secondhand smoke remain in household air: analysis of PM2.5 data from smokers' homes.
abstract: BACKGROUND
  More than 80% of secondhand smoke (SHS) is invisible to the human eye, and smokers are often unaware of how much SHS is produced when they smoke at home. Very little is known about how long SHS particles remain suspended in the air within household settings.
  
  
  METHODS
  Data from a series of studies where fine particulate matter (PM2.5) concentrations were measured every minute in homes were used to identify the PM2.5 peak produced by SHS from the last cigarette smoked of the day. The time taken for this peak to reduce by 50% was calculated, as was the time between the peak and a return to the World Health Organization's (WHO) 24-hr guidance value for PM2.5 of 25 µg/m(3).
  
  
  RESULTS
  From more than 230 days worth of 1-min resolved PM2.5 data gathered from 103 smoking households, 140 suitable peaks were identified. The median (interquartile range [IQR]) for the time for the SHS peak to decay by 50% was 55 (23-116) min, and the median (IQR) for the peak to reduce to the WHO guidance value for PM2.5 was 160 (90-313) min.
  
  
  CONCLUSIONS
  SHS remains in household air for a considerable period after smoking a cigarette. This information is likely to be of use in public health information campaigns and in interventions to encourage smokers to make their home smoke-free.
authors.affiliation: Scottish Centre for Indoor Air, Respiratory Group, Division of Applied Health Sciences, University of Aberdeen, Aberdeen, UK; Center for Human Exposure Science, Institute of Occupational Medicine, Edinburgh, UK sean.semple@abdn.ac.uk.
authors.forename: Sean
authors.initials: S
authors.lastname: Semple
authors.affiliation: Scottish Centre for Indoor Air, Respiratory Group, Division of Applied Health Sciences, University of Aberdeen, Aberdeen, UK;
authors.forename: Norul
authors.initials: N
authors.lastname: Latif
mesh_terms: D005240:Feasibility Studies; D006798:Housing / Q000639:trends*; D006801:Humans; D010316:Particle Size; D052638:Particulate Matter / Q000032:analysis*; D012907:Smoking / Q000639:trends*; D013997:Time Factors; D014028:Tobacco Smoke Pollution / Q000032:analysis*
chemical_list: D052638:Particulate Matter; D014028:Tobacco Smoke Pollution