Quantifying Residential Emissions of Volatile Organic Compounds and Their Influence on Urban Air Pollution

As volatile organic compound (VOC) emissions have declined, the gap between top down and bottom up emission inventories has widened. This gap may be attributable to volatile chemical products (VCPs), cooking emissions, and other unquantified indoor sources emitted outdoors. Studies have considered VOC emissions from certain types of commercial buildings, however emissions from residential dwellings have been largely overlooked

Here we evaluate the residential contributions to outdoor air pollution. We combine speciated VOC and ventilation measurements from the HOMEChem campaign with speciated VOC and ventilation measurements from two single-family homes during normal occupancy. Across a broad range of species, measured VOC concentrations were routinely an order of magnitude higher indoors than outdoors. Emitted VOCs from episodic release events tended to decay at the ventilation rate, supporting the inference that their major fate is transport outdoors.

Reactivity with the OH radical is used to assess the air quality impact of residential VOC emissions. When unoccupied, indoor OH reactivity at the HOMEChem site was 4 times greater than outdoors, with monoterpenes making the largest contribution. With the addition of occupancy and activities, the indoor-to-outdoor OH reactivity ratio increased to more than 10, and monoterpenes were again the largest source, followed by ethanol from cooking. These results corroborate data from a normally occupied residence, where we find living space OH reactivity to be an order of magnitude greater than outdoors. As in HOMEChem, monoterpene and ethanol emissions are large contributors to OH reactivity.

Combining ventilation rates with concentration measurements and reaction rate constants allows us to quantify the OH reactivity emitted from a residence. Detailed ventilation measurements of the occupied residence show that the living space is the major source of reactivity emissions, although separate emissions from the attic are significant. Time resolved measurements show that the emitted reactivity from the living space increases in the evening, coinciding with cooking. Occupant driven "spikes" in reactivity further indicate the occupancy is a key driver of the residential emission profile of VOCs and the corresponding emission of reactivity from residences.