Estimation of VOC emission factors from flux measurements using a receptor model and footprint analysis

Fluxes of 18 volatile organic compounds (VOCs) collected during May to July 2008 from a tower platform 60 m above the surface in an urban Houston residential area were analyzed using receptor-oriented statistical models and an analytical flux-footprint model to resolve daytime source specific emissions rates. The Multilinear Engine version 2 (ME-2) was used to determine that five sources were responsible for the measured flux at the tower: (i) vehicle exhaust, (ii) a foam plastics industrial source with significant pentane emissions, (iii) consumer and commercial solvent use emissions, (iv) a biogenic emissions source dominated by isoprene, and, (v) evaporative fuel emissions. The estimated median daytime (0700-1900 CST) hourly emission rate from the foam plastics industry was 15.7 ± 3.1 kg h−1, somewhat higher than its permitted hourly emission rates. The median daytime vehicle exhaust VOC emission rate of 14.5 ± 2 g h−1 vehicle−1, was slightly higher than our estimation using the Motor Vehicle Emission Simulator (MOVES) with a county-representative vehicle fleet of year 2008 (11.6 ± 0.2 g h−1 vehicle−1). The median daytime evaporative fuel VOCs emission rate from parked vehicles was 2.3 ± 1.0 g h−1 vehicle−1, which is higher than MOVES estimations and could not be explained by the age of the vehicle fleet, indicating either locally higher evaporative emission sources in the footprint or an underestimation of evaporative emissions by MOVES, or both.