[1] Carbon dioxide is a stable constituent of the atmosphere that has no major terrestrial sinks other than atmospheric transport in the absence of photosynthetic activity by plants. In urban atmospheres, CO 2 mixing ratios are often elevated above ambient by large local sources from combustion. We measured CO 2 mixing ratios and the isotopic composition of CO 2 at four locations in the Salt Lake Valley, Utah, during a persistent cold pool event in the winter of 2004. The results showed a strong influence of atmospheric stability and the height of the capping inversion on CO 2 mixing ratios and suggested that during persistent cold pool events the air mass beneath the capping inversion can be relatively well mixed. Spatial and temporal patterns in the isotopic composition of CO 2 and the relationship between particulate concentrations and CO 2 mixing ratio support this interpretation. These results suggest that CO 2 mixing ratio, which is abundant and relatively easily measured in urban atmospheres, can provide information about complex wintertime atmospheric transport and mixing as well as carbon cycling in urban mountain basins.

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In this study, the concentration of sub-micron particulate matter (PM) and its associated metals concentration have been discussed. Monitoring of sub-micron particulate matter has been made by using Leland legacy sample pump with five-stage Sioutas Cascade Impactor. Total, 150 samples from urban and sub urban areas of western part of India were analysed using ICP-OES. For PM 1.0-2.5 , PM 0.50-1.0 and PM 0.25-0.50 the average mass concentration ranged from 28.33 to 38.86 µg m −3 , 30.46 to 39.44 µg m −3 , 25.43 to 46.30 µg m −3 for indoor environment, while outdoor environment concentrations ranged from 23.15 to 54.01 µg m −3 , 22.38 to 36.20 µg m −3 , 22.32 to 44.30 µg m −3 , respectively. On the other hand, in sub urban area, the average mass concentrations ranged from 23.15 to 69.44 µg m −3 , 27.72 to 51.73 µg m −3 , 17.72 to 54.01 µg m −3 for indoor environment, while for outdoor environment, the average mass concentrations ranged from 30.86 to 77.16 µg m −3 , 23.15 to 54.01 µg m −3 , 24.25 to 46.30 µg m −3 for PM 1.0-2.5 , PM 0.50-1.0 and PM 0.25-0.50 , respectively. Among all eight toxic metals, Al and Fe were found to be abundant. Human health risk factor also being calculated which showed that these metals were threat to human life. The sources of the sub-micron particulate matter associated metals in outdoor air were found to be the emissions from industries, vehicular activities, and dust from construction sites and in indoor it was mostly from cooking, cleaning and other human activities.

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