DETECTION OF EXCESS AMMONIA EMISSIONS FROM IN-USE VEHICLES AND THE IMPLICATIONS FOR FINE-PARTICLE CONTROL

The emission rate for ammonia from in-use vehicles is calculated based on measurements made inside a Los Angeles roadway tunnel. Using fleet distributions by vehicle age and type, known catalyst distributions, and fuel economy by model year and vehicle type and attributing all am monia to vehicles equipped with three-way catalysts or three-way catal ysts plus oxidizing catalysts (dual-bed catalysts), we estimate an ave rage ammonia emission rate of 72 mg km(-1) for these vehicles, or 61 m g km(-1) driven by the vehicle fleet as a whole. These emissions can e manate from vehicles running under rich air-fuel conditions, with thre e-way catalytic converters designed to reduce NOx to N-2 and O-2 in ad dition forming NH3. Resulting calculations estimate ammonia emissions of 24-29 t of NH3 day(-1) from the vehicle fleet for the South Coast A ir Basin (SoCAB) that surrounds Los Angeles. This represents an increa se in the daily emissions of ammonia attributable to motor vehicles in the SoCAB from 2% of basin wide emissions before the introduction of catalyst-equipped automobiles to 15% based on the current experiment. The air basin wide emission rate of ammonia from motor vehicles is com pared to ammonia emissions from livestock waste decomposition at local dairies, and the implications for control of fine particle ammonium n itrate concentrations are discussed.