This study investigates the secondary organic aerosol (SOA) formation potential of carburetor motorcycles exhaust. This type of two-wheeler is a popular means of transport in many Asian cities. A volatility-based numerical model was employed to predict SOA formation from a fleet of motorcycles in Tehran, capital of Iran. The fleet was a combination of four-stroke, gasoline-powered motorcycles with different engine displacement volumes. Total hydrocarbon (THC) emission factors of all motorcycles were previously measured in a chassis dynamometer laboratory according to cold start Euro-3 emissions certification test procedures. Due to incomplete combustion and lack of control on exhaust emissions, unburned fuel was assumed to be a good surrogate for the exhaust of carburetor motorcycles, regarding SOA formation. 150 cc engine and 200 cc engine motorcycles had the highest SOA formation potential, under atmospheric oxidant concentration, while 125 cc engine motorcycles had the highest SOA emission factor (travel- and fuel-based). It was found out that SOA emission factor of 125 cc engine motorcycles could increase up to 20%, three to five years after production. Average SOA formation from carburetor motorcycles in the present study was 4 times higher than Euro-4 passenger cars and 20 times higher than direct emission of particles from Euro-2 motorcycles and on (according to EMEP/EEA levels for PM_2.5 emission factors). Carburetor motorcycles with 180 cc engine volume in the present study, had the lowest SOA formation potential.

这项研究调查了化油器摩托车排气的二次有机气溶胶（SOA）形成潜力。这种类型的两轮车是许多亚洲城市中流行的交通工具。基于波动率的数值模型被用来预测伊朗首都德黑兰的摩托车车队形成的SOA。车队是由四冲程，汽油驱动的摩托车和不同的发动机排量组成的。以前，所有摩托车的总碳氢化合物（THC）排放因子都是根据底盘测功机实验室根据欧3排放标准冷启动认证测试程序进行测量的。由于不完全燃烧和对废气排放的缺乏控制，就SOA的形成而言，未燃烧的燃料被认为是化油器摩托车排气的良好替代品。150 毫升发动机和200  cc发动机摩托车在大气氧化剂浓度下具有最高的SOA形成潜力，而125  cc发动机摩托车具有最高的SOA排放因子（基于旅行和燃料的排放）。结果发现，在生产后的三到五年内，125 cc发动机摩托车的SOA排放因子 可以增加高达20％。在本研究中，化油器摩托车的平均SOA形成量是欧4乘用车的4倍，比欧2摩托车的直接排放高出20倍（根据PM _2.5排放因子的EMEP / EEA水平）。180 cc化油器摩托车  在本研究中，发动机的体积具有最低的SOA形成潜力。