Diurnal-, Seasonal- and Site-Dependent Variability in Ground-level Total Non-Methane Hydrocarbon in Nagpur City of Central India

Abstract

Temporal & spatial variations in ground-level total non-methane hydrocarbon (TNMHC) were studied in Nagpur urban agglomeration (UA) for a year over three seasons viz. post-monsoon (September-October), winter (January-February) and summer (May-June) in 2013–14. Ground-level TNMHC showed low to moderate spatial (over residential, commercial, traffic intersections, residential cum commercial sites) and temporal (at 7:00, 13:00; 18:00 and 23:00 h in all three seasons) variations. There was no specific increasing or decreasing trend with time, either within a day or a season. Daily mean concentration of TNMHC (averaged over concentrations at 7:00, 13:00; 18:00 and 23:00 h) ranged from 0.88–1.73 ppmV, 1.75–4.04 ppmV and 1.20–1.53 ppmV at residential sites; 2.99–6.47 ppmV, 1.52–7.38 ppmV and 0.98–1.63 ppmV at traffic site; 0.83–1.15 ppmV, 2.03–3.24 ppmV, 1.1–1.70 ppmV at residential cum commercial sites and 1.05–4.79 ppmV, 6.2–8.58 ppmV, 0.34–0.64 ppmV at the purely commercial site, during post-monsoon, winter and summer, respectively. Occasional spikes (TNMHC>10 to <13.6 ppmV) were observed on three occasions over two sites in winter but reasons thereof remained unidentified. During Diwali Festival (in post-monsoon) marked by large-scale firecrackers bursting, observed TNMHC concentrations hovered around 3–5 ppmV, which almost matched with 90th percentile of other post-monsoon concentrations. Highest mean seasonal TNMHC concentration was observed during winter, followed by means of post monsoon and summer seasons while mean ground-level TNMHC concentrations on weekdays were slightly higher (1.17–1.21 times) than weekends over all seasons.