Resurvey of the Corticolous Lichen flora of Epping Forest
central London in the 1960s (UK National Air Quality Archive) to current levels below 8ppb (20
µg m3).
Fig. 1. Sulphur dioxide concentrations (µg per m3) in London
Black smoke from industrial activity has also declined but finer particulate matter (known as PM10)
of varied composition is still widespread with new sources mainly attributed to transport. The
influence of local traffic on the Forest is not quantified and there are no continuous measurements
taken in Epping Forest. Diffusion tubes have been used to monitor nitrogen dioxide and computer
generated maps, derived from local emissions inventories of traffic flow in the area, show that
roadside concentrations are at their peak. The M25 motorway to the north, Al04, A406, Al2, A503
to the south, and congestion arising along the arterial roads at the Wake Arms arc all contributing to
a climate of nitrogenous compounds and fine particulate matter compounded by a dominant south-
westerly wind that carries London's pollution towards Epping Forest (Plate 1).
Recent review and assessment procedures by local authorities have compared air quality in the
area against Objectives for human health for seven pollutants: sulphur dioxide, nitrogen dioxide,
carbon monoxide, lead, 1,3 butadiene, benzene and fine particulate matter (DEFRA 2000). Two
such Obj ectives arc exceeded in the area. In Waltham Forest the annual mean Objectivc for nitrogen
dioxide, 21 ppb (40 µgm3), is exceeded close to all major roads and the daily mean PM10 Objective
of 50 ug m3 is regularly exceeded across the borough generally, but more importantly close to the
A406, All, A106 and A104 located in or close to Epping Forest. Because the health Objectives
are breached Waltham Forest Council has declared the area an Air Quality Management Area
(AQMA) and is currently preparing an Air Quality Action Plan, which, together with national
measures, will propose steps to reduce pollution. The vegetation Objectives do not apply in urban
areas on economic grounds although it should be noted that the Objective for oxides of nitrogen of
16 ppb (30 µgm3), being more stringent than health standards for nitrogen dioxide alone, is widely
exceeded across the area. The Objective for sulphur dioxide is not exceeded.
70 Essex Naturalist (New Series) 20 (2003)