BMC Public Health 2006, 6:42 http://www.biomedcentral.com/1471-2458/6/42 Background Second hand smoke (SHS) exposure causes of a range of serious adverse health effects in children, adults and preg- nant women [1-3]. In the UK it is estimated that domestic exposure to secondhand smoke causes at least 3,600 deaths annually, while workplace exposure accounts for around 700 deaths per year Internationally, the introduction of legislation to ensure workplaces and other public places are smokefree is a key current public health policy issue. In many countries and states, such as Ireland, New York, New Zealand and Nor- way, comprehensive smokefree legislation has been intro- duced. In the UK, Scotland and Northern Ireland propose to do the same. However, the UK government in its public health White Paper Choosing Health proposed introducing partial smokefree legislation for England with exemptions including for pubs and bars that do not prepare and serve food, and private members clubs [4]. A number of groups have criticised the logic of the partial exemption of pubs and bars as studies have shown that the highest levels of SHS exposure occur in pubs and bars [5-7]. The policy may also maintain or even increase dif- ferentials in ill health due to smoking as there is evidence that pubs and bars in more deprived areas are less likely to serve food and more likely to allow unrestricted smoking [8,9]. We set out to test hypothesis that pubs and bars from more deprived areas and non food-serving pubs have higher levels of particulate air pollution. Methods Setting and sampling The study was performed in four wholly or mainly urban Local Authority areas across the north west of England – Burnley, Bury, Blackburn with Darwen, and Manchester. Each includes areas with relatively high levels of depriva- tion. The sampling frame for the study was the bars and pubs from the four study areas which had previously par- ticipated in a survey of North West hospitality premises [8]. We contacted pubs by letter and excluded those that did not wish to take part from the sampling frame. We also excluded town/city centre pubs as the area-based dep- rivation score is less likely to be representative of the socio-economic status of its customers. Finally, we excluded a number of pubs from the study during the data collection period as these were deemed to be too unsafe by the researchers. Pubs were allocated an area-based deprivation score (Index of Multiple Deprivation [IMD] 2004 [10]) by map- ping their postcode to the Census Super Output Area. Super Output Areas were categorised into deprivation quintiles (IMD 1 – 5) for all Super Output Areas across the North West. We identified four categories of pubs and bars. Firstly, we dichotomised pubs into affluent (IMD 1– 3) and deprived (IMD 4 or 5). Secondly, we divided pubs into those which did and did not prepare and serve food based on their response in the earlier survey [8]. We aimed to recruit four pubs from each of the four categories in each study area (64 pubs in total). In order to maximise the contrast between the groups, for each study area and pub category we sampled randomly first from quintile 5 or 1 pubs in the sampling frame, then if necessary from quintile 4 or 2, and finally from quintile 3, stopping once four pubs plus 3–4 reserves were identified. Data collection We aimed to perform air quality measurements in four pubs per evening, one from each category, visited in sequence. To ensure a range of measurements we sampled on four separate days of the week (Tuesday-Friday). Pub occupancy may vary by day of the week and time of night. Therefore, we included a pub from each category on every evening and varied the order of monitoring the pubs so that a pub from each of the four categories was monitored once first, once second, once third and once fourth within each of the four study areas. Occasionally, to minimise transport time, the order of visiting pubs or choice of pubs had to be slightly modified from this plan. Data collection was carried out using portable air quality monitors according to a protocol modified from one developed for a US study [11]. Pubs were visited unan- nounced by two or more investigators. The investigators carried a battery operated real time aerosol monitor (TSI SidePak AM510 Personal Aerosol Monitor – TSI, Inc., St. Paul, USA) in a small bag. The monitor was zero cali- brated each evening. It was fitted with a 2.5 µm impactor to sample and record the average levels of RSP (PM2.5) over one minute periods. The air flow rate was 1.7 l/min. A length of Tygon™ tubing was attached to the inlet of the SidePak, with the other end left protruding outside the bag. The recorded measurements were downloaded to a PC for analysis. A calibration factor of 0.32 was applied based on calibration work with a ThermoMIE personalD- ataRAM model pDR-1200 real-time aerosol monitor (ThermoAndersen, Inc., Smyrna, GA, USA). This type of monitor had been used in a previous similar study in Del- aware and has been calibrated against standard pump- and-filter gravimetric methods [12]. At each venue we identified the busiest room of the pub where smoking was allowed, and selected a central area for monitoring, away from any open external doors or windows, kitchen areas, and not in the immediate vicinity (< 1 metre) of anyone smoking (unless this were not pos- sible). Smoke free areas or rooms were avoided. To avoid Page 2 of 6 (page number not for citation purposes)