§ Mr. Dalyell
To ask the Secretary of State for the Environment, Transport and the Regions if he will make a statement on trends in the levels of(a) ammonia, (b) benzene, (c) mercury and (d) phosgene in the atmosphere. 
§ Mr. Meacher
[holding answer 8 June 1999](a) Ammonia—My Department has been funding a nationwide network of around 70 sites to measure the ambient concentrations of ammonia since 1996. To date, there is not a sufficiently long dataset to discern authoritatively any trends, although early indications are that there is substantial seasonal and inter-annual variability. There are larger concentrations in spring and summer, and the largest concentrations are in warm, dry years. On the basis of natural variability, monitoring for more than five years will be necessary to clearly detect changes in response to changes in national emissions. Numbers of livestock and nitrogen fertiliser usage, which are the main sources of ammonia, have declined since the mid 1980s.
Earlier ad-hoc monitoring campaigns from this period are not sufficient to demonstrate increased concentrations in the 1980s compared with the present. Much longer term datasets of precipitation chemistry and deposition have shown that atmospheric ammonia increased substantially between 1950 and the 1980s, which can be explained by both increases in livestock numbers and nitrogen fertiliser inputs.
(b) Benzene—My Department has funded the continuous real-time measurement of benzene in the air since 1993. There are now 13 sites in the network, including roadside, urban background, and rural locations. In 1997, the running annual mean for benzene from this network ranged from (rural) 0.5–(urban centre) 2.1 parts per billion. To date, there is not a sufficiently long dataset to discern authoritatively any trends. Results of the monitoring are available in the Department's Digest of Environmental Statistics, and are available on the Department's internet site.
(c) Mercury—Mercury is predominantly present in the UK atmosphere as either particulate mercury or other semi-volatile mercury compounds. This leads to measurement problems in that it is difficult to measure the two phases in the same sample. My Department has been measuring mercury at three sites—Chilton in Oxfordshire, Styrrup in north Nottinghamshire and Wraymires in the Lake District. These are all relatively remote locations. Measurements have been taken of particulate mercury and of mercury in rain. Table 1 lists the atmospheric concentrations of mercury (ng m-3) at rural locations. The particulate mercury is only a small fraction of the total, perhaps 4 per cent. Table 2 gives mercury concentrations in rain water (.tg 1-1) at rural locations, mercury is rarely detectable in rain water. There is no trend to speak of in either of these measures of mercury concentrations, except that analytical detection limits have improved markedly in recent years.376W
Table 1: Atmospheric mercury concentrations (ng m-3) at rural locations
Year Chilton Styrrup Wraymires 1992 0.14 0.52 <0.1 1993 1.6 2.1 0.29 1994 0.11 0.32 0.18 1995 0.095 0.21 <0.1 1996 0.18 0.37 0.23 1997 0.07 <0.2 0.19 1998 0.22 0.72 0.49
Table 2: Mercury concentrations in rain water (µg I-1) at rural locations
Year Chilton Styrrup Wraymires 1992 <1 <6 <6 1993 <1 <1 <1 1994 0.026 0.031 0.019 1995 <0.1 0.2 <0.1 1996 <0.1 <0.1 <0.1 1997 <0.005 <0.008 0.009 1998 <0.006 <0.006 <0.006
(d) Phosgene—My Department has no information on the levels of phosgene in the atmosphere.