Simultaneous long-term measurements of near-surface air pollutants at an urban station, New Delhi, were studied during 2005–2012 to understand their distribution on different temporal scales. The annual mean mass concentrations of nitrogen dioxide (NO$_{2}$), sulphur dioxide (SO$_{2}$), particulate matter less than 10 $\mu$m (PM$_{10}$) and suspended particulate matter (SPM) were found to be 62.0 $\pm$ 27.6, 12.5 $\pm$ 8.2, 253.7 $\pm$ 134 and 529.2 $\pm$ 213.1 $\mu$g m$^{3}$, respectively. The 24-hr mean mass concentrations of NO$_{2}$, PM$_{10}$ and SPM were exceeded on $\sim$ 27%, 87% and 99% days that of total available measurement days to their respective National Ambient Air Quality Standard (NAAQS) level. However, it never exceeded for SO$_{2}$, which could be attributed to reduction of sulphur in diesel, use of cleaner fuels such as compressed natural gas, LPG, etc. The mean mass concentrations of measured air pollutants were found to be the highest during the winter/post-monsoon seasons, which are of concern for both climate and human health. The annual mean mass concentrations of NO$_{2}$, PM$_{10}$ and SPM showed an increasing trend while SO$_{2}$ appears to be decreasing since 2008. Air mass cluster analysis showed that north–northwest trajectories accounted for the highest mass concentrations of air pollutants (more prominent in the winter/post-monsoon season); however, the lowest were associated with the southeast trajectory cluster.

The variations in the ambient concentrations of particulate matter (SPM and PM$_{10}$) and gaseous pollutants (SO$_{2}$ and NO$_{2}$) at Clock tower (CT), Rajpur road (RR) and Inter State Bus Terminal (ISBT) station in Dehradun city, Uttarakhand, India are analysed for the period of 2011–2014. Mean concentrations are observed to be higher during pre-monsoon season as compared to the winter and monsoon. PM$_{10}$ and SPM concentrations with maximum values of 203 $\pm$ 23 and 429 $\pm$ 49 $\mu$g m$^{-3}$, respectively, during winter, are found to exceed the national standards by factors of 2 and 3. Winter-time elevated pollution in Dehradun is attributed to the lower ventilation coefficient (derived from Era interim model fields) and minimal precipitation. Nevertheless, the SO$_{2}$ and NO$_{2}$ levels are observed to be within the criteria notified by the Central Pollution Control Board (CPCB), India. Correlation analysis shows profound impacts of the meteorology and local dynamics on the observed variations in observed trace species. Additionally, the stronger inter-species correlation variations (r=0.79 for SO$_{2}$ with NO$_{2}$, and r=0.89 for PM$_{10}$ with SPM), which may suggest their origin from common sources. Analysis of ‘Air Quality Index (AQI)’ variations indicates unhealthy atmospheric conditions near the major city centers and bus station. More observations in the region are highly desirable to understand the dispersion of the enhanced pollution in the Dehradun valley.