what kind of pollution issues does it face?
Nitrogen dioxide pollution
Oxford Street
In 2014, a report by a King's College, London scientist showed that Oxford Street had the world's highest concentration of nitrogen dioxide pollution, at 135 micrograms per cubic metre of air (μg/m). 
where is oxford street? City of Westminster, West End of London, England what is it? A major road
wiki:11710162
Oxford Street [SEP] Pollution
In 2014, a report by a King's College, London scientist showed that Oxford Street had the world's highest concentration of nitrogen dioxide pollution, at 135 micrograms per cubic metre of air (μg/m). The figure was an average that included night-time, when traffic was much lower. At peak times during the day, levels up to 463 μg/m were recorded – over 11 times the permitted EU maximum of 40 μg/m. Because of diesel-powered traffic (buses and taxis), annual average nitrogen dioxide concentrations are around 180 μg/m. This is 4.5 times the EU target of 40 μg/m (Council Directive 1999/30/EC).