A novel approach to investigating indoor/outdoor pollution links: combined magnetic and PAH measurements

In a preliminary study, paired indoor and outdoor air sampling was conducted at three locations around the city of Lancaster, UK to examine the influence of combustion sources on air quality by measuring particulate concentrations, particulate magnetic properties and polyaromatic hydrocarbons (PAHs). With one exception (an indoor suburban air sample), outdoor air samples had higher total suspended particulates (TSP), particle-bound PAH concentrations and magnetic remanence (IRM) values. IRM values were highest for the week-day, outdoor city centre samples and then declined in the sequence: Sunday, city centre > suburban/residential > Lancaster University campus. These data indicate traffic as the major particle-bound PAH, particulates and magnetic source, particularly as sampling was conducted during July in the absence of any space heating. The indoor air samples revealed a wide variation in pollutant concentrations, characterised by higher vapour levels of 2-3 ring PAHs, variable TSP concentrations and variable but generally low IRMs. The differences in PAH concentrations, TSP and IRMs between outdoor and indoor environments indicate limited ingress of outdoor air pollutants to the indoor environment in this study. Our combined PAH and magnetic data identify specific and distinctive indoor pollution signals for each of our sampled sites, reflecting distinct sources. One site, the suburban house, has anomalously high IRM, TSP and particle-bound PAHs. A possible source for these is a cast iron, wood-burning stove (even though not lit). The city centre indoor site is characterised by high TSP and very low IRMs but high values of the magnetic ratio of anhysteretic remanence:saturation remanence, indicative of ultrafine (submicrometre) magnetic grain sizes. The source for this city centre indoor signature is unidentified but may reflect the occupant smoking and/or lighting candles. The indoor campus sample was affected by loss-