The UK Black Smoke Network(Network managed and operated for Defra and the DAs by the National Physical Laboratory)Black Smoke measurements were the earliest systematic measurements of air pollution by particulate matter in the United Kingdom, with records dating back to the 1920s. Air is sampled through a filter and the darkness of the stain, measured by optical reflectance, is converted to a Black Smoke Index, given in units of µgm-3. In 2005, monitoring of Black Smoke ceased to be a regulatory requirement in the United Kingdom, with particulate matter being regulated as PM10 and PM2.5. In that year, Defra commissioned an independent review of the UK urban network for measurement of Black Smoke, SO2 and NO2. Its recommendations for Black Smoke monitoring included continuing a network of about 20 sites, some of which should be at AURN locations. The resulting new UK Black Smoke Network commenced operation on 1st September 2006. The design of the Network was planned to incorporate 11 existing Black Smoke sites and 10 Black Smoke samplers in AURN stations. Samplers were installed at the AURN (section A3.1) sites between October 2006 and March 2007. The design of the Network was planned to incorporate 11 existing Black Smoke sites from the old Smoke and SO2 Network, and to install 10 Black Smoke samplers in AURN stations. The sites are listed below. 
Black Smoke sampling uses the 8-port sampler that has historically been used in the UK network, based on the standard method BS 1747 Part 11, ISO 9835. The principle of the 8-port sampler method involves drawing air at a constant flow rate of around 1.4 l/min through a Whatman Number 1 cellulose filter, so that about 2 m3 of air (at ambient conditions of temperature and pressure) is sampled for each daily sample. Suspended particulate matter is collected on the filter over an area determined by a choice of clamp - in this case with a one inch diameter - forming a dark stain. The inlet, an upturned funnel, is not specifically designed to be size selective, and has been shown in one study to collect the approximate size fraction PM4.5.
The 8-port sampler is designed with eight pairs of filter clamps for weekly operation, providing daily sampling from a midnight-to-midnight basis. The timed eight-port valve is set to switch over at midnight to expose a fresh filter paper each day. Weekly visits are made to change filter papers and to record weekly sample volumes and flow rates. Black smoke concentrations are then estimated by means of a reflectance measurement. The darkness of the stain is measured with an EEL M43D reflectometer, the reflectance being determined relative to a blank filter of the same type. The instrument uses a light bulb to give a broad band source that is reflected back from the smoke stain to a photo-sensitive element and produces a reading between 0% and 100% reflectance. NPL measures the reflectance of all of the filters sampled by the network, whereas, previously, reflectometry measurements were performed by local Councils using their own reflectometers. The measured reflectance, sampled volume and filter area are used to calculate the concentration of dark particulate matter in the sampled air, as Black Smoke Index, with units of .gm-3, using the relationship given in BS 1747: Part 2: 
where: C = concentration in µg/m3 V = volume of sampled air in ft3 R = reflectometer reading (%) The above relationship is only valid for a one inch diameter filter clamp - an additional factor is required for other clamp sizes. This relationship is also only valid for values of R above 40%, which was true for all samples measured in the Network over recent years. The results of the first full year of the new Black Smoke Networks operation are compiled in a report available on the Air Quality Archive at www.airquality.co.uk/archive/reports/cat05/0706141352_2006_Annual_Report_final.pdf |
