Abstract
Abstract. Nitrate aerosols make a very major contribution to PM2.5 and PM10 in western Europe, but their sources and pathways have not been fully elucidated. An Aerosol Time-of-Flight Mass Spectrometer (ATOFMS) and a Compact Time of Flight Aerosol Mass Spectrometer (C-ToF-AMS) were deployed in an urban background location in London, UK, collecting data as part of the REPARTEE-I experiment. During REPARTEE-I, daily PM10 concentrations ranged up to 43.6 μg m−3, with hourly nitrate concentrations (measured by AMS) of up to 5.3 μg m−3. The application of the ART-2a neural network algorithm to the ATOFMS data characterised the nitrate particles as occurring in two distinct clusters (i.e. particle types). The first (33.6% of particles by number) appeared to be locally produced in urban locations during nighttime, whilst the second (22.8% of particles by number) was regionally transported from continental Europe. Nitrate in locally produced aerosol was present mainly in particles smaller than 300 nm, whilst the regional nitrate presented a coarser mode, peaking at 600 nm. In both aerosol types, nitrate was found to be internally mixed with sulphate, ammonium, elemental and organic carbon. Nitrate in regional aerosol appeared to be more volatile than that locally formed. During daytime, a core of the regionally transported nitrate aerosol particle type composed of organic carbon and sulphate was detected.
Highlights
Nitrate aerosol is a major component of the total aerosol mass in western Europe
nitrogen oxides (NOx) is oxidized by OH to form HNO3, whilst during night time the NO3 radical may be formed by reaction between NO2 and ozone and can be converted to nitric acid via its thermal equilibrium with N2O5 (Carslaw et al, 1997; Brown et al, 2005)
Back trajectories of the air masses arriving at the measurement site were calculated for 00:00 and 12:00 for each day of the campaign, depicting the path taken by the air mass reaching the sampling site over the previous five days
Summary
Nitrate aerosol is a major component of the total aerosol mass in western Europe. It is formed chemically in the atmosphere from the precursor species ammonia (NH3) and nitric acid (HNO3). Sources of ammonia include agricultural sources such as livestock housing and the storage and spreading of manures as well as oceans, biomass burning, crops and soil (Bouwman et al, 1997). Typical sources of nitrogen oxides (NOx), which are the main precursor of nitric acid, include fossil fuel combustion, soils, biomass burning and lighting. NOx is oxidized by OH to form HNO3, whilst during night time the NO3 radical (which is photolysed during the day) may be formed by reaction between NO2 and ozone and can be converted to nitric acid via its thermal equilibrium with N2O5 (Carslaw et al, 1997; Brown et al, 2005). Sub-micrometre nitrate aerosol is predominantly present in the form of ammonium nitrate (NH4NO3), a semi-volatile compound
Sign-in/Register to view highlights & summary 
Published Version (
Free)
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call