Source Apportionment of Volatile Organic Compounds, CO, SO2 and Trace Metals in a complex urban atmosphere

Abstract A commixture of gasphase compounds including carbon monoxide (CO), sulphur dioxide (SO2), volatile organic compounds (VOCs) and trace metals were collected at a site located at the urban/industrial interface in Houston, Texas. Positive Matrix Factorization (PMF) analysis yielded nine factors: gas/crude oil (21.3±5.5%), isoprene emission (17.0±7.1%), Si-rich (14.6±1.3%), liquefied petroleum gas (LPG) (11.2±4.0%), traffic (10.6±0.4%), Fluidized-bed Catalytic Cracking (FCC)/high temperature operations (7.2±4.3%), oil refinery (6.8±0.9%), soil and road dust (6.2±0.6%), and petrochemical industries (5.0±5.0%). Daytime and nighttime PMF runs were carried out to see potential differences among and within emission sources. Notable findings include: (1) Nocturnal isoprene emission was identified from traffic exhaust and industrial sources. (2) LPG emissions were higher during the day most likely due to temperature dependent evaporative processes. (3) V/Ni and SO2/V ratios reveal greater contribution from crude oil in the merged natural gas/crude oil emission factor. Corrosion might be responsible for emitting metals (i.e., Cr, Cu, Mo, Ni) from oil refineries during nighttime. (4) In the soil and road dust factor, metals relevant to plant physiological processes are mostly retained by the plants while the lanthanoids and other metals (i.e. Y, Pb, Mn, Ga, Ba) are more prone to physical removal during the day. (5) FCC/high temperature operations are dominated by metals at night. (6) The traffic factor increases during the day possibly due to the higher number of vehicles. Bivariate polar plots suggest the Houston Ship Channel area as the primary emission source for LPG, natural gas/crude oil, FCC/high temperature operations, and petrochemical industries.