Public bus system worldwide transports daily more than 34 million people; therefore, air quality inside buses is an important urban air pollution issue. Airborne microbiological composition and abundance was examined inside five different fuel type buses (diesel (EURO IV and EURO V), hybrid diesel (HD), compressed natural gas (CNG), hybrid natural gas (HCNG) and electric vehicle (EV)) from Barcelona bus system, inside and outside the tourist bus and different periods of campaigns (summer: May–September and winter: November–March). Quantitative PCR was used to quantify total bacteria, Penicillium/Aspergillus and Cladosporium sp. and Kinetic Chromogenic Limulus Amebocyte Lysate (LAL) Assay for endotoxins. The targeted 16S rRNA genes were amplified and sequenced to asses bacterial community composition and biodiversity. Regarding the targeted microorganisms, the results showed low bioaerosol concentrations, being fungi and endotoxins below the detection limit, although bacterial airborne has a geometric average of 10³ equivalent E. Coli genomes/m³. Airborne bacterial community biodiversity showed that Actinobacteria and Proteobacteria were the most abundant Phylum in the different sampled buses and in the two seasons (summer: May–September and winter: November–March). While regarding to genera taxonomic category, the different fuel type buses presented a high overlap degree, being Cutibacterium the most abundant and Paracoccus the one only detected inside. The different seasons showed that the different taxonomic genera decrease from summer: May–September to winter: November–March and in this case Paracoccus was the most abundant. Overall, biodiversity inside buses is greatly affected by the presence of humans inside, but also by the outdoor sources at the moment of the sampling, and the seasonal period, more than the type of bus.

全球公共巴士系统每天运送超过3400万人次；因此，公交车内的空气质量是一个重要的城市空气污染问题。检查了来自以下地区的五种不同燃料类型的公共汽车（柴油（EURO IV和EURO V），混合柴油（HD），压缩天然气（CNG），混合天然气（HCNG）和电动汽车（EV））中的空气传播微生物成分和丰度。巴塞罗那巴士系统，旅游巴士的内部和外部以及不同时期的运动（夏季：5月至9月，冬季：11月至3月）。定量PCR被用于定量总细菌，青霉/曲霉和Cladosporium sp。和动力学发色Li变形细胞溶解物（LAL）内毒素测定。靶向的16S rRNA基因被扩增并测序以评估细菌群落组成和生物多样性。关于目标微生物，结果显示较低的生物气溶胶浓度，即真菌和内毒素低于检测极限，尽管细菌空气传播的几何平均数为10 ^3个当量大肠杆菌基因组/ m ³。空气传播的细菌群落生物多样性表明，放线菌和变形杆菌是在不同采样巴士中以及两个季节（夏季：5月至9月和冬季：11月至3月）中最丰富的Phylum。就一般分类而言，不同的燃油类型客车呈现出很高的重叠度，表皮细菌最丰富，而副球菌仅在内部被发现。不同的季节表明，从夏季：5月至9月至冬季：11月至3月，不同的分类学种类有所减少，在这种情况下，副球菌最为丰富。总体而言，公交车内的生物多样性不仅受到公交车内人的存在的影响，而且还受到采样时和季节的室外来源的影响，而不仅仅是公交车的类型。