Role of anthropogenic emissions and meteorology on ultrafine particle bursts over a high altitude site in Western Ghats during pre-monsoon

The ultrafine particle number concentration and size distribution during pre-monsoon (spring) over a high altitude location, Ooty (11.3 °N, 74.4 °E, 2240 m amsl) in Western Ghats, the highest peak in South India, are examined using campaign based ground observations. The total number concentrations are in the range ∼1000-3000 cm−3 with significant increase (2-4 folds) during the periods of ultrafine particle (UFP) (diameter < 100 nm) bursts. The UFP burst happens mostly during afternoon/evening with significant enhancement in number concentrations of nucleation (Nnuc) and Aitken (NAitk) mode particles. Examination of the association of these events with prevailing meteorology and trace gas concentrations revealed weaker dependence in general. However, the association between NOX and the UFP concentration indicates the possibility of common source for both. During the high concentrations of UFP, local winds originated predominantly from south/south west directions of the study location where the valley region with significant anthropogenic activities is located. Time of occurrence of the UFP bursts, trace gas concentrations and direction of the winds points towards the role of valley winds in transporting plume of pollutants to the mountain top observatory during the daytime.