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The aggregate from the weigh hopper is dropped into the mixer(pug mill) and dry-mixed for 6 to 10 seconds. The liquid asphalt is then dropped into a pug mill where it is mixed for an additional period of time. Total mixing time is usually less than 60 seconds. Then the hot mix is conveyed to a hot storage silo or is dropped into a truck and hauled to a job site. Emissions from hot mix plants may be divided into ducted production emissions,pre-production fugitive dust emissions, and other production-related fugitive emissions. Pre-production fugitive dust sources include vehicular traffic generating dust on paved and unpaved roads, aggregate material handling, and other aggregate processing operations. Ducted emissions are usually collected and transported by an industrial ventilation system having one or more fans, eventually to be emitted to the atmosphere through some type of stack. The most significant ducted source of emissions is the rotary drum dryer. The dryer emissions consist of water; PM; product of combust; and small amounts of organic compounds, including hazardous air pollutants. Other potential process sources include the hot-side conveying,classifying,and mixing equipment, which are vented either to the primary dust collector(along with the dryer gas) or to a separate dust collection system. Emission controls for PM emissions from the dryer and vent lines include dry mechanical collectors, scrubbers, and fabric filters, and the use of primary dust collection equipment such as large diameter cyclones, skimmers,and settling chambers. Air emissions were determined for the operation of the asphalt batching processing. The air emission calculations accounted for the proposed production levels(400,000 tons per year), the 1 number,types, and size of equipment,and the type of material processed and emission controls, if any. The emission factors were determined using the methodology found in Section 11.1 of EPA's AP-42. Table AQ-4 presents the emission factors for the asphalt processing operations. _ Additional emissions include benzene,acetaldehyde,ethyl benzene,PAHs,and various metals. PM,CO, and VOC emissions also occur during batch mix plant load-out,silo filling, and asphalt r storage, based on asphalt volatility,mix temperature,predictive emission factor equations found in AP-42 Section 11.1 (Table 11.1-14), and HAP speciation profiles. TABLE AQ-4 EMISSION FACTORS FOR ASPHALT PROCESSING' Emission Point PM10 CO SO2 NOx VOC Dryer,hot screen,mixer° 0.4 0.0046 0.025 0.0082 Uncontrolled 4.5 Venturi or wet scrubber 0.14 Fabric Filter 0.042 I SOURCE:Compilation of Air Pollutant Emission Factors,AP-42,Fifth Edition,Volume 1:Stationary Point and Area Sources,Section 11.1 Hot Mix Asphalt Plants,December 2000.