Physical and chemical characteristics of particles from rubber-wood combustion in a natural rubber sheet smoking process were studied. Experimental parameters include wood moisture content and wood-burning period. The size distribution of smoke particles was measured by using an 8-stage Andersen air sampler. Total smoke particle concentration was determined by collecting particles using a modified high volume sampler. Polycyclic Aromatic Hydrocarbons (PAHs) were extracted with Benzene-Ethanol by using ultrasonic technique and analyzed by HPLC/UV detection. Results show that the size distribution of smoke particles is single-mode in which the mass median aerodynamic diameter (MMAD) is 0.68 μm and the average smoke concentration is 15.806 mg/m 3 . This is equivalent to a mass emission to workplace of 4.33 kg/month/room. The smoke particle concentration and associated PAH concentration clearly depend on the wood moisture content and burning period. The highest PAH concentration and smoke particle concentrations were found to be 60.59 to 118.06 μg/m 3 and 23.35 to 47.54 mg/m 3 , respectively, for a wood moisture content of 37.4 to 73.6% d.b. (dry basis) at the initial period. Smoke particle-bound PAHs are dominated by 4-6 ring PAH compounds that contribute to more than 60% of the total PAHs.

The workplace environment in factories producing ribbed smoked sheet rubber (RSS), the interiors which are heavily contaminated by wood burning smoke, was evaluated with a focus on the concentration of suspended particulates and particle-bound PAHs as well as workers' exposure in the breathing zone during the period January, -February, 2008 in Thailand. Seasonal changes in particulate and PAH concentrations are discussed in relation to the amount of RSS produced, wind direction, ventilation type and the geometry of the factory building. The concentration of particulate matter in the workplace was shown to increase nearly linearly with RSS production while being influenced by the wind direction to the open sides of the building and wind speed. Particulate concentrations in the workplace and in the worker's breathing zone were lower than those for other common occupational exposure limits. However, rather high PAH concentrations of 97.4 ± 129 ng/m 3 and 142 ± 184 ng/m 3 were found in the workplace and in the breathing zone, respectively. BaP TEQ concentrations in the workplace ranging from 21.4 to 91.0 ng/m 3 were similar to those in a sinter plant. The workers' exposure to PAHs was similar to that in a sinter plant, a metal recycling plant, a paving bitumen manufacturing plant and a carbon black manufacturing plant. The mass fraction of PAHs in particles in the RSS factory was as high as 0.30 BaP TEQ ng/μg, much higher than that in a carbon black plant (0.004-0.01 BaP TEQ ng/μg). The results reported herein suggest that the workers in the RSS factory have a somewhat high health risk from exposure to PAHs. Natural ventilation by the addition of roof turbines was insufficient in terms of reducing PAHs levels in the workplace although a roof ridge vent was functional and had a positive effect.

Natural rubber is a main commodity of Thailand, half of which is formed into ribbed smoked sheets (RSS). Fuel wood is burned during RSS production to heat and dry the rubber sheets. Smoke from the burning wood contains chemical species in particles and gases, notably polycyclic aromatic hydrocarbons (PAHs). In this study, the influence of smoke from fuel-wood burning by rubbersmoking cooperatives on atmospheric air in the neighboring town of Hat Yai, Songkhla Province in southern Thailand, was evaluated for the year 2005. The particle size distributions of ambient air in downtown Hat Yai and Prince of Songkla University (PSU) clearly showed bi-modal behavior, indicating multiple sources of particles. TSP was generally low, averaging 45.6 and 46.2 µg/m 3 for downtown Hat Yai and PSU, respectively. The TSP depended on precipitation, particularly when precipitation was high. The correlation between TSP and rubber sheet production from all rubber cooperatives in Songkhla Province is clear. PAH size distributions of ambient air particles clearly showed single-modal behavior, suggesting that most of the PAHs are associated with small particles.The relationship between wood burning and PAHs in ambient air in Hat Yai and PSU is also clear.Low PAH concentrations during the dry season could result partly from wind direction (E to NE), which blows inland from the Gulf of Thailand. During the rainy season, PAH concentration at both locations was low; however, it was inversely proportional to the precipitation. Hence, rubber sheet production, wind direction and precipitation are important determinants of PAH concentration in Hat Yai area.

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