Seasonal variability of ambient NH3, NO, NO2 and SO2 over Delhi.

We present the diurnal and seasonal variability of ambient NH3, NO, NO2 and SO2 over Delhi, India. Ambient NH3, NO and NO2 were measured continuously during winter, summer and autumn seasons using NH3- and NOx-analyzer, which operates by chemiluminescence method with a higher estimation efficiency (> 90%) than the chemical trap method (reproducibility 4.7%). Prominent diurnal, day-to-day and seasonal variations of ambient mixing ratio of NH3, NO, NO2 and SO2 were observed during the study period. Seasonal variation with higher mixing ratio in winter was observed for all measured trace gases except NO. Day-night variation of all measured trace gases observed was higher in winter in comparison with summer. Late morning increase in NO2 mixing ratio might be attributed to conversion of NO to NO2 with the interaction of O3.

Study on concentration of ambient NH3 and interactions with some other ambient trace gases.

We present diurnal variation of ambient ammonia (NH(3)) in relation with other trace gases (O(3), CO, NO, NO(2), and SO(2)) and meteorological parameters at an urban site of Delhi during winter period. For the first time, ambient ammonia (NH(3)) was monitored very precisely and continuously using ammonia analyzer, which operates on chemiluminescence method. NH(3) estimation efficiency of the chemiluminescence method (>90%) is much higher than the conventional chemical trapping method (reproducibility 4.5%). Ambient NH(3) concentration reaches its maxima (46.17 ppb) at night and minimum during midday. Result reveals that the ambient ammonia (NH(3)) concentration is positively correlated with ambient NO (r(2) = 0.79) and NO(2) (r (2) = 0.91) mixing ratio and negatively correlated with ambient temperature (r(2) = - 0.32). Wind direction and wind speed indicates that the nearby (approximately 500 m NW) agricultural fields may be major source of ambient NH(3) at the observational site.

Depolarization ratio measurement using single photomultiplier tube in micropulse lidar.

The conventional dual polarization micropulse lidar uses two separate photomultiplier tubes (PMT) to detect both the copolarized and cross-polarized beam. The prominent sources of error in the depolarization ratio measurement are mismatch in PMT, improper selection of discriminator threshold and unequal PMT high voltage. In the present work a technique for the measurement of lidar depolarization ratio using only one PMT sensor has been developed. The same PMT detects both copolarized and cross-polarized lidar backscatter. A stepper motor is used along with the mirrors to bring both the received polarization signals over the PMT window. Application of the same PMT minimizes the error caused in the depolarization ratio measurement due to error in photon counting of an individual channel. The design description of this technique along with the preliminary results depicting its functionality has been mentioned in this article.