Seasonal variations in size distribution, water-soluble ions, and carbon content of size-segregated aerosols over New Delhi

Abstract

Size distribution, water-soluble inorganic ions (WSII), and organic carbon (OC) and elemental carbon (EC) in size-segregated aerosols were investigated during a year-long sampling in 2010 over New Delhi. Among different size fractions of PM, PM was the dominant fraction (45%) followed by PM (20%), PM (15%), PM (10%), and PM (10%). All size fractions exceeded the ambient air quality standards of India for PM. Annual average mass size distributions of ions were specific to size and ion(s); Ca, Mg, K, NO, and Cl followed bimodal distribution while SO and NH ions showed one mode in PM. The concentrations of secondary WSII (NO, SO, and NH) increased in winters due to closed and moist atmosphere whereas open atmospheric conditions in summers lead to dispersal of pollutants. NHand Cawere dominant neutralization ions but in different size fractions. The summer-time dust transport from upwind region by S SW winds resulted in significantly high concentrations of PM and PM and PM. This indicted influence of dust generation in Thar Desert and its transport is size selective in nature in downwind direction. The mixing of different sources (geogenic, coal combustions, biomass burning, plastic burning, incinerators, and vehicular emissions sources) for soluble ions in different size fractions was noticed in principle component analysis. Total carbon (TC = EC + OC) constituted 8-31% of the total PM mass, and OC dominated over EC. Among EC, char (EC1) dominated over soot (EC2 + EC3). High SOC contribution (82%) to OC and OC/EC ratio of 2.7 suggested possible role of mineral dust and high photochemical activity in SOC production. Mass concentrations of aerosols and WSII and their contributions to each size fraction of PM are governed by nature of sources, emission strength of source(s), and seasonality in meteorological parameters.

Seasonal variation of carbonaceous species in PM1 measured over residential area of Delhi, India

“…A total of thirty-six aerosol samples (three samples per month) were collected. Similar types of protocols have been observed to follow by other researchers [56][57][58]. The filter was also pre-heated in a muffle furnace at 700 ˚C for 5 h in order to lower the carbon contents (OC and EC) in the blank QMF [59].…”

Understanding sources and processes using chemistry of fine and coarse particles simultaneously collected from different windward locations in N-NW India

“…This study domain represents a unique geographical region, good natural laboratory for the studies on particle generation, transportation and depositional processes along dominant wind path during summer season and their environmental implications. More details about the study area can be accessed from our previous work 25,26,18 . Meteorological data for the study period were taken from Resources Laboratory: National Oceanic and Atmospheric Administration (ARL-NOAA) (http://www.arl.noaa.gov/).…”

“…PM 2.5 and PM 2.5-10 particles were collected on quartz ber lters (QFFs) of 20×25 cm size and perforated QFFs of 13 ×18 cm size placed on impactor plates, respectively. Both types of QFFs were pre-combusted and pre-conditioned 18 . Each sample was collected for 24 h duration.…”

“…Some samples were rejected too in the eld itself due to electricity problems, breakdown of instrument and damage of lters under strong windy conditions. Field blanks and laboratory blanks were also collected and handled in a manner similar to that of actual sample 18,19 .…”

“…Fine particles (PM 2.5 ) are largely contributed by anthropogenic sources with high residence time and are inhaled while breathing and cause direct health effects compared to coarse particles 15,16 . New Delhi, the capital of India, is facing severe air quality problems during summer season due to wind-assisted transport of particles from the Thar Desert region in upwind direction 17,18,19 . Rapid urbanization, industrialization and transportation system further amplify the problems of air pollution in urban area of downwind (New Delhi) region 20,13,18 .…”