Abstract: Elemental and water-soluble ionic compounds (WSICs) of atmospheric aerosols (total suspended particulate TSP) and some gaseous pollutants (SO2, NO2 and O3) from a coastal, semi-urban and rural site in and near Dar es Salaam, Tanzania were investigated during dry and wet seasons of January 2005November 2007. Na+, Ca2+, SO42−, NO3− and Cl− made up the dominant fraction of WSICs during the dry season with average concentrations ranging from non-detectable (n.d.)5.4, 0.262.6, 0.7414.7, 0.41.5 and 1.13.4 μg m−3, respectively, while in the wet season, from n.d. up to 1.7, 1.2, 4.4, 2.1 and 3.0 μg m−3, respectively. The total air concentrations of the detected elements (Al, Si, S, Cl, K, Ca, Fe and Zn) showed seasonal and site-specific variation in the range of 7.526.6 with an average of 14.5 μg m−3. Most of the air concentrations of pollutants were observed to decrease with increasing distance from the coastal site, which is under urban and industrial pollutant emissions. Sulphur and nitrogen oxidation ratios during the dry season ranged from 0.08 to 0.91 and 0.013 to 0.049, respectively, while they were between 0.090.65 and 0.0020.095, respectively, in the wet season. These values indicate the photochemical oxidation of SO2 and a high extent of NO3−formation in the atmosphere. Neutralization ratios revealed the presence of acidic SO42− and NO3− aerosols. Principal component analysis identified sea spray, local combustion, vehicular traffic, biomass burning and re-suspended road dust as dominant sources of aerosols at the studied coastal and semi-urban sites. However, at the rural site, besides sea spray, crustal sources, soil dust re-suspension and long-range transport are the possible origins of suspended particulates.

Abstract: The surface of the aerial parts of the plant, also termed the phyllosphere, is a selective habitat for microbes. The bacterial composition of the phyllosphere depends on host plant species, leaf characteristics, season, climate, and geographic location of the host plant. In this study, we investigated the effect of an urban environment on the bacterial composition of phyllosphere communities. We performed a passive biomonitoring experiment in which leaves were sampled from ivy (Hedera sp.), a common evergreen climber species, in urban and non-urban locations. Exposure to traffic-generated particulate matter was estimated using leaf biomagnetic analyses. The bacterial community composition was determined using 16S rRNA gene sequencing on the Illumina MiSeq. The phyllosphere microbial communities of ivy differed greatly between urban and non-urban locations, as we observed a shift in several of the dominant taxa: Beijerinckia and Methylocystaceae were most abundant in the non-urban phyllosphere, whereas Hymenobacter and Sphingomonadaceae were dominating the urban ivy phyllosphere. The richness, diversity and composition of the communities showed greater variability in the urban than in the non-urban locations, where traffic-generated PM was lower. Interestingly, the relative abundances of eight of the ten most dominant taxa correlated well with leaf magnetism, be it positive or negative. The results of this study indicate that an urban environment can greatly affect the local phyllosphere community composition. Although other urban-related factors cannot be ruled out, the relative abundance of most of the dominant taxa was significantly correlated with exposure to traffic-generated PM.