<sod >The western end of Oxford Street near Marble Arch, registered an annual average of 150 micrograms per cubic metre of air â the second highest level in the country.< eod>< sod > Â  The second highest level of NO2 measured in the country is at the western end of Oxford Street near Marble Arch, with an annual average of 150 micrograms per cubic metre of air.< eod>