Measurement report: Interpretation of wide-range particulate matter size distributions in Delhi

Abstract

Abstract. Delhi is one of the world's most polluted cities, with very high concentrations of airborne particulate matter. However, little is known about the factors controlling the characteristics of wide-range particle number size distributions. Here, new measurements are reported from three field campaigns conducted in winter and pre-monsoon and post-monsoon seasons at the Indian Institute of Technology campus in the south of the city. Particle number size distributions were measured simultaneously, using a scanning mobility particle sizer and a GRIMM optical particle monitor, covering 15 nm to >10 µm diameter. The merged, wide-range size distributions were categorized into the following five size ranges: nucleation (15–20 nm), Aitken (20–100 nm), accumulation (100 nm–1 µm), large fine (1–2.5 µm), and coarse (2.5–10 µm) particles. The ultrafine fraction (15–100 nm) accounts for about 52 % of all particles by number (PN10 is the total particle number from 15 nm to 10 µm) but just 1 % by PM10 volume (PV10 is the total particle volume from 15 nm to 10 µm). The measured size distributions are markedly coarser than most from other parts of the world but are consistent with earlier cascade impactor data from Delhi. Our results suggest substantial aerosol processing by coagulation, condensation, and water uptake in the heavily polluted atmosphere, which takes place mostly at nighttime and in the morning hours. Total number concentrations are highest in winter, but the mode of the distribution is largest in the post-monsoon (autumn) season. The accumulation mode particles dominate the particle volume in autumn and winter, while the coarse mode dominates in summer. Polar plots show a huge variation between both size fractions in the same season and between seasons for the same size fraction. The diurnal pattern of particle numbers is strongly reflective of a road traffic influence upon concentrations, especially in autumn and winter, although other sources, such as cooking and domestic heating, may influence the evening peak. There is a clear influence of diesel traffic at nighttime, when it is permitted to enter the city, and also indications in the size distribution data of a mode < 15 nm, which is probably attributable to CNG/LPG vehicles. New particle formation appears to be infrequent and is, in this dataset, limited to 1 d in the summer campaign. Our results reveal that the very high emissions of airborne particles in Delhi, particularly from traffic, determine the variation in particle number size distributions.

Extreme Concentrations of Nitric Oxide Control Daytime Oxidation and Quench Nocturnal Oxidation Chemistry in Delhi during Highly Polluted Episodes

“…The instrument setup and calibration methodology are as described by Squires et al HONO was measured using a long-path absorption photometer (LOPAP) with baseline measurements taken at regular intervals (8 h). Further details along with measurement descriptions for the aerosol surface area, photolysis rates, and meteorological data can be found in refs and .…”

“…To combat transport pollution, the Government of National Capital Territory of Delhi introduced prohibitive regulations impacting the transport of goods into and out of the city. Prohibitions on the movement of goods vehicles vary across Delhi but generally restrict HGVs during peak times for passenger vehicles [07:00–11:00 and 17:00–23:00 Indian Standard Time (IST)] . These daytime restrictions lead to increased HGV movement at night, and thus increased nighttime emissions.…”

“…Prohibitions on the movement of goods vehicles vary . 22 These daytime restrictions lead to increased HGV movement at night, and thus increased nighttime emissions. Delhi also suffers from unfavorable meteorological conditions, with shallow boundary layer heights and low wind speeds leading to stagnant conditions, especially during the winter.…”

Direct measurement of the deposition of submicron soot particles on leaves of Platanus acerifolia tree

“…These results implied that fossil fuels dominated submicron soot in the sampling site of urban Nanjing and at the suburban site of Lu'an during summertime. 47 The submicron soot from fossil fuels in these two sites was supposed to be emitted from industrial sources and mobile sources. 46 Our source apportionment study illustrated that submicron soot was mainly emitted from the combustion of fossil fuels in the urban areas of Nanjing, China.…”

Vertical Profiles of Particle Number Size Distribution and Variation Characteristics at the Eastern Slope of the Tibetan Plateau

“…In northern China, northwest or northeast winds have been found to promote the formation of nucleation mode particles, while easterly winds facilitate the growth of these particles [14,39]. In the context of Delhi, India, coarse mode particles are predominant before the onset of the monsoon season, whereas accumulation mode particles become dominant afterward [40].…”