Evidence for increasing concentrations of primary PM10 in London

Although annual mean concentrations of PM10 in and around London reduced during the 1990s, concentrations have been relatively stable since, with small increases during 2001–2003. A modelling method was used to apportion the measured annual mean concentration of PM10 between primary, and secondary and natural sources at monitoring sites in and around London between 1997 and 2004. The annual mean concentration of PM10 from primary sources reached a minimum during 1998. Between 1998 and 2003 the greatest change in the annual mean concentration of primary PM10 occurred at sites adjacent to busy roads: Marylebone Road (7.0±2.6 μg m−3), Wandsworth 4 (6.0±1.1 μg m−3) and Ealing 2 (4.5±1.4 μg m−3). The smallest change in the concentration of PM10 from primary sources occurred at background locations in towns outside London. It is therefore likely that the additional primary PM10 arose from road traffic. These increases in PM10 from primary sources contradict emissions inventory estimates that indicate reductions in primary PM10. The annual mean concentration of PM10 from secondary and natural sources declined by 2.0±3.0 μg m−3 or 11±16% between 1997 and 2003. The annual mean concentration of PM10 from these sources reduced until the year ended 1st July 2001 and then increased during the remainder of 2001, 2002 and 2003.