Analysis of the air pollution climate of a central urban roadside supersite: London, Marylebone Road

The London Marylebone Road monitoring site is a roadside supersite adjacent to highway carrying 80–90,000 vehicles per day on six lanes in street canyon. Data from the Automatic Urban and Rural Network (AURN), Black Carbon Network, Hydrocarbon Heavy Metal Particle Size Number Composition covering period 2009 2018 were analysed determine short-term (diurnal, weekly seasonal) long-term variations geographic source attribution. contribution of emissions relative background sites (roadside increment) pollution climate was also investigated. trend analysis shows significant decline regulated pollutants such as particulate matter fractions (?4.0%; ?3.93%/yr for PM2.5 PM10 respectively) gas phase associated with vehicular (?5.5%; ?1.22% ?2.1%/yr CO, NOx NO2 respectively), although concentrations SO2 O3 have remained relatively constant over years. Equivalent carbon (eBC) total particle number count declined years whereas heavy metals show mixed results (only Cu, Ni V downward trends). inorganic ionic components fraction, elemental (EC) organic (OC) volatile compounds all generally declining trends period. Assessment diurnal elevated fractions, nitrogen oxides, CO at periods corresponding traffic rush hours, peaked afternoon when there less titration due lower NO concentrations. pattern eBC Total Count are similar strong influence. Cl, Mg, K Na levels no systematic throughout, their presence likely controlled by meteorological conditions, Ca showing high because resuspension deposited dust resulting turbulence created movement, eroded road-surface material. Ammonium nitrate lowest during temperature high, probably reflective semi-volatile nature, sulphate producing peak around mid-day. VOCs, exception ethane, give bimodal peaks typical related emission plots more than other emitted gaseous pollutants. Ethane leakages supply pipes. weekday (Monday – Friday) increases traffic-related weekends volumes, reverse observed O3. marine aerosol days week, while Ca, NH4+, NO3? SO42? maximum weekend. seasonal variations; springtime maximum, traffic-emitted (NO, NOx, EC, OC etc) giving winter increase emission, mixing depth poor dispersion. Particulate summertime nature some components. variability, concentration driven higher wind speed conditions. summer VOCs minimum wintertime isoprene increased summertime. canyon circulation causes sampling North air northerly winds, but enhanced winds southerly component. There sizeable increment above local both exhaust (particulate mass eBC) non-exhaust (heavy metals). However, increments species, which include secondary components, not significant, indicating that they mainly regional transport Polar contributions (EC OC), direction. long-range mainland Europe occurs aerosol. Ratios OC/EC particles shown steady rapid reduction EC OC.