Potential source identification for aerosol concentrations over a site in Northwestern India

doi:10.1016/j.atmosres.2015.09.022

Atmospheric Research

Volume 169, Part A, 1 March 2016, Pages 65-72

https://doi.org/10.1016/j.atmosres.2015.09.022 Get rights and content

Highlights

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The number size distribution was dominated by fine particles during winter season.
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The log normal size distribution curves reveals that the particle size < 0.8 µm is key contributor in winter for higher ANC.
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The average AE values differs considerably during summer (< 0.3) than winter (> 1.0) season.
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Interestingly, mean AOT values during summer and winter months do not differ largely over the study site.
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Potential Source Contribution Function (PSCF) suggests coarse particles at site came from south-west direction (Thar Desert).

Abstract

The collocated measurements of aerosols size distribution (ASD) and aerosol optical thickness (AOT) are analyzed simultaneously using Grimm aerosol spectrometer and MICROTOP II Sunphotometer over Jaipur, capital of Rajasthan in India. The contrast temperature characteristics during winter and summer seasons of year 2011 are investigated in the present study. The total aerosol number concentration (TANC, 0.3–20 μm) during winter season was observed higher than in summer time and it was dominated by fine aerosol number concentration (FANC < 2 μm). Particles smaller than 0.8 μm (at aerodynamic size) constitute ~ 99% of all particles in winter and ~ 90% of particles in summer season. However, particles greater than 2 μm contribute ~ 3% and ~ 0.2% in summer and winter seasons respectively. The aerosols optical thickness shows nearly similar AOT values during summer and winter but corresponding low Angstrom Exponent (AE) values during summer than winter, respectively. In this work, Potential Source Contribution Function (PSCF) analysis is applied to identify locations of sources that influenced concentrations of aerosols over study area in two different seasons. PSCF analysis shows that the dust particles from Thar Desert contribute significantly to the coarse aerosol number concentration (CANC). Higher values of the PSCF in north from Jaipur showed the industrial areas in northern India to be the likely sources of fine particles. The variation in size distribution of aerosols during two seasons is clearly reflected in the log normal size distribution curves. The log normal size distribution curves reveals that the particle size less than 0.8 μm is the key contributor in winter for higher ANC.

Introduction

Aerosols are a major component of our environment and play an important role in the climate of the Earth-atmosphere system by means of their direct and indirect impact on climate (Schwartz et al., 1995). Atmospheric aerosol particles are one of the most variable components of the Earth's atmosphere and influence the energy budget and climate (Remer et al., 2005).

Aerosol number concentration and size distribution plays a crucial role in shaping Earth's radiation budget by scattering and absorption of sunlight in atmosphere. Scattering and absorption coefficient is an important parameter which strongly depends on particle's physical and chemical property. One of the key physical parameters of aerosols is the number size distribution, and especially for the climate effects, the size distribution in the sub-micron range. Most of the monitoring networks across the world measures PM₁₀ and PM_2.5 (mass of particulate matter smaller than 10 and 2.5 μm in aerodynamic diameter, respectively). Measurement of aerosol particle number size distribution was carried out in many cities of the world i.e. Birmingham (Harrison et al., 1999), Atlanta (Woo et al., 2001), Helsinki (Buzorius et al., 1999, Hussein et al., 2004), Leipzig (Wehner and Wiedensohler, 2003), Pittsburgh (Stanier et al., 2004), Beijing (Wu et al., 2008). These studies showed the seasonal variation with low aerosol number concentration in summer while high during winter.

In India the majority of observations are from coastal or urban locations. A high particulate matter concentration (Bhanarkar et al., 2002, Mitra and Sharma, 2002, Gajananda et al., 2005, Chatterjee et al., 2010) has been reported from Indian cities. Kumar and Sarin (2009) reported mass concentrations of fine particulate matter less than or equal to 2.5 μm (PM_2.5) and coarse (PM_10–2.5) mode aerosols to vary from 1.6 to 46.1 and 2.3 to 102 μg/m³, respectively over the annual seasonal cycle during 2007 at a high-altitude site (Mt. Abu) in a semi-arid region. The aerosol number concentration during fireworks and vehicular emission is carried out by researcher in India (Singh et al., 2003, Kulshrestha et al., 2004, Pant et al., 2006, Pant et al., 2010, Majumdar and Nema, 2011, Sharma et al., 2011, Prakash et al., 2013, Saha et al., 2014; etc.).

However, at large, the semi-arid region over India there is a very limited number of long-term datasets of sub-micron aerosol particle size distributions. Even from the Indo gangetic basin, where several intensive measurement campaigns have been carried out during recent years, no size distribution measurements that cover a full year have been published (see, for example, the review by Lawrence and Lelieveld (2010)). Most probably it is the first study of its kind to understand the aerosol number concentration behavior and its origin during two different seasons over this region.

The possible sources of aerosols on a regional scale over India have only recently received attention. In the present study, we identify potential source regions of the factors during the event using Potential Source Contribution Function (PSCF), and combine it with particle number concentration for source identification. Several observations of aerosol concentrations have been made over Northwestern India (Verma et al., 2013, Payra et al., 2015). The general trend over the site during pre-monsoon season was high AOT and low AE values and vice-versa in winter (Payra et al., 2013). The in-situ measurements for 2011 have also shown the similar trends of AOT and AE. However, AOT and AE were a little bit higher and lower than the mentioned respective values. In-situ measurements are thus important especially at strategic places like Jaipur which can help determine the regional radiation budget over a semi-arid region.

In continuation to above, in this paper the concentration of different sized particles, during two contrasting seasons i.e. winter and summer time are studied over Jaipur, Northwestern India. Specially, the characteristics of modes appearing in measured particle size distributions in combination with MICROTOP II sunphotometer data are investigated. The purpose of this study is to determine the characteristic of aerosol size distribution at Jaipur during two extreme seasons by examining the simultaneously measured size-separated number concentrations.

Section snippets

Site description

Jaipur, the study area, lies in desert belt receiving most of the rain during late summer months. The measurement site is located about 6 km to east from the Jaipur city centre. The climate of the region has three distinct seasons; summer (April–June), monsoon (July–September) and harsh winter (December–January). Fig. 1 shows meteorological conditions of site retrieved from National Center for Environmental Prediction (NCEP)—National Center for Atmospheric Research (NCAR) reanalysis data. The

Variations of particle number concentrations

Size distributions of atmospheric aerosols may be described in terms of modes which characterize their size ranges. Sub micrometer particles are classified into the total aerosols number concentration TANC modes (D_p = 0.3–20 μm), fine aerosols number concentration i.e. FANC (D_p = 0.3–2 μm) and the coarse i.e. CANC (D_p ≥ 2 μm).

Summary and conclusion

During an extended study at Jaipur site (450 m amsl), the particle number size distribution (diameter D_p = 0.3–20 μm) and aerosols optical thickness were measured on a continuous basis. The winter and summer seasons with a contrast temperature characteristics in the year 2011 are investigated in the present study.

The number size distribution was dominated by fine particles during winter season. The log normal size distribution curves reveals that the particle size less than 0.8 μm has key

Acknowledgments

We greatly acknowledge and thank the SERB, Department of Science and Technology (DST), and Govt. of India for the financial support under research project SR/S4/AS:39/2009. The authors would like to thank the Editor and anonymous reviewers for suggestions that helped in improving the presentation of the revised manuscript. Authors gratefully acknowledge the NOAA Air Resources Laboratory (ARL) for the provision of the HYSPLIT transport and dispersion model and/or READY website (//www.arl.noaa.gov/ready.php

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Potential source identification for aerosol concentrations over a site in Northwestern India

Highlights

Abstract

Introduction

Section snippets

Site description

Variations of particle number concentrations

Summary and conclusion

Acknowledgments

Atmos. Environ.

Atmos. Environ. (1967)

Atmos. Environ.

Atmos. Environ.

Remote Sens. Environ.

Atmos. Environ.

Atmos. Environ.

Atmos. Environ.

Atmos. Environ.

Atmos. Environ.

Chemosphere

Atmos. Environ.

Atmos. Environ.

Atmos. Environ.

Atmos. Environ.

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