Measurements of mass concentrations of particulate matters (PM2.5 and PM10) and mixing ratio of carbon monoxide (CO) were made at an urban site of Udaipur (24.58°N, 73.68°E) in India from April 2010 to March 2011. Concentrations of PM2.5, PM10 and CO show strong diurnal and seasonal variations. The highest concentrations coincide with the rush traffic and lower nocturnal boundary layer depth. The lowest concentrations in the afternoon hours are attributed to the dilution caused by higher boundary layer height and reduced traffic. The levels of trace constituents during the weekend were significantly reduced compared to the weekdays of observations. The daily PM2.5, PM10 and CO varied in the large ranges of 8–111 µg/m3, 28–350 µg/m3 and 145–795 ppbv, respectively. PM2.5 and CO show strong seasonality with higher and lower values during winter and monsoon seasons, respectively, while PM10 shows highest value during the pre-monsoon season. Flow of cleaner marine air and negligible biomass burning resulted in lower values in the monsoon season. Long-rang transport and extensive biomass burning caused higher values in winter and pre-monsoon seasons. Back trajectories show seasonal shift in the long- range transport which is consistent with the seasonality of aerosols and CO. Except for the monsoon season, mass concentrations of PM2.5 and PM10 show good correlation (typically r2 > 0.5). Relations of PM2.5 and PM10 with CO varied with the season but show good correlations (r2 > 0.5) during the winter season, while poor correlation during monsoon. The correlations suggest dominance of combustion related emissions particularly during winter season. Monthly emission ratios of ΔPM2.5/ΔPM10, ΔPM2.5/ΔCO and ΔPM10/ΔCO varied in the ranges of 0.19–0.31 µg/m3/ppbv, 0.05–0.10 µg/m3/ppbv and 0.15–0.25 µg/m3/ppbv, respectively. The mass concentration of PM2.5 tends to decrease with the increasing wind speed, while PM10 increases with wind speed.