Elsevier

Atmospheric Environment

Volume 143, October 2016, Pages 152-163
Atmospheric Environment

Inorganic ions in ambient fine particles over a National Park in central India: Seasonality, dependencies between SO42−, NO3, and NH4+, and neutralization of aerosol acidity

https://doi.org/10.1016/j.atmosenv.2016.08.037Get rights and content

Highlights

  • PM2.5 mass and its ions were measured for two years over a National Park in India.

  • Average mass contribution of major ions NH4+, K+, SO42−, and NO3 was 21%.

  • Thermal power plants emissions appear to be a significant source of SO42− and NO3

  • SO42− and NO3 were neutralized almost entirely by NH4+ and K+.

  • Aerosol was acidic only during pre-monsoon and monsoon seasons.

Abstract

Twelve hour integrated ambient fine particles (PM2.5) were collected over an Van Vihar National Park (VVNP), in Bhopal, Central India. Samples were collected on filter substrates every-other-day for two years (2012 and 2013). In addition to PM2.5 mass concentration, water soluble inorganic ions (WSIIs) were also measured. Further, on-site meteorological parameters including temperature, wind speed, wind direction, relative humidity, rainfall and atmospheric pressure were recorded. During 2012, the average PM2.5 concentration was 40 ± 31 μgm−3 while during 2013 it was 48 ± 50 μgm−3. Further, in about 20% of the samples the 12 h integrated fine PM mass exceeded the daily (24 h) average standards (60 μgm−3). This observation suggests that the PM2.5 mass concentration at the study site is likely to be in violation of the National Ambient Air Quality Standard (NAAQS), India. During the study period the sum of three major ions (SO42−, NO3, and NH4+) accounted for 19.4% of PM2.5 mass on average. Air parcel back trajectory ensembles revealed that emissions from thermal power plants were likely to be the main regional source of particulate SO42− and NO3 measured over VVNP. Further, local traffic activities appeared to have no significant impact on the concentrations of PM2.5 and its WSIIs constituents, as revealed by a day-of-the-week analysis. PM2.5 mass, SO42−, NO3, and NH4+ showed a pronounced seasonal trend with winter (Jan, Feb) and post-monsoon (Oct, Nov, Dec) highs and pre-monsoon (Mar, Apr, May) and monsoon (Jun, Jul, Aug, Sep) lows, during both 2012 and 2013. Further, when the sum of SO42− and NO3 constituted greater than 90% of water soluble inorganic anions by mass, they were linearly dependent on one another and moderately anti-correlated (r2 = 0.60). The molar ratios of NH4+ and non-sea salt SO42− were examined to understand the aerosol neutralization mechanisms and particulate NO3 formation. An assessment of these ratios and subsequent analyses suggested that in NH4+ rich samples, NO3 and non-sea salt SO42− were almost entirely neutralized by NH4+. In NH4+ poor samples, in addition to NH4+ non-sea salt K+ played a role in acidity neutralization. These observations are unlike those reported for PM10 and total suspended particles (TSP) over other locations in India, where mineral aerosol species (specifically Ca2+) played an important role in neutralizing acidic species. Additionally, both during 2012 and 2013, the aerosol acidity showed a pronounced seasonality - the aerosol was alkaline or near-neutral during the winter and post-monsoon seasons, while during the pre-monsoon and monsoon seasons it was acidic.

Section snippets

Introduction and purpose

Across locations in the world, typically, water soluble inorganic ions (WSIIs) and carbonaceous compounds (organic and elemental) constitute a major fraction of fine particulate matter (aerodynamic diameter ≤2.5 μm also known as PM2.5) mass (Mandal et al., 2014, Squizzato et al., 2013). Inhalation of PM2.5 is reported to induce adverse health effects related to asthma, chronic bronchitis, heart diseases and respiratory diseases (e.g., Laden et al., 2000). However, the role of specific chemical

Sampling

This work formed one component of a comprehensive study aimed at the source apportionment of ambient fine PM (PM2.5) mass and an assessment of its radiative effects over Van Vihar National Park (VVNP), Bhopal located in Central India (Fig. 1). Co-located samples of fine PM were collected on various filter substrates to achieve the study objectives.

Chemical analyses

Samples collected on Teflo® filters were used for PM2.5 mass measurements in accordance with the Research Triangle Institute standard operating protocols (RTI, 2008) and details of mass measurement are discussed in Supplemental Text S1.

The samples collected on Nylasorb® membrane filters were used for quantitation of WSIIs by ion chromatography (IC). A Metrohm® 883 Basic IC Plus isocratic system was used for WSIIs analyses. The details of sample preparation and IC analyses for anions and cations

Data description and analyses

During the study period (January 2012 to December 2013), 332 Teflo® and 312 Nylasorb® filters were collected. Metrological parameters including temperature (˚C), wind speed (m/s), wind direction (˚), relative humidity (%), atmospheric pressure (hPa) and rainfall (mm) were recorded on all sampling days. Although 366 samples were to be collected as per the sampling schedule, a few filters were not collected due to pump failure, logistics and other operational issues.

The study period was

Statistical characterization

The summary statistics for fine PM mass and its WSIIs for the entire study duration (January 2012 to December 2013) are shown in Table 2. In this table, in addition to percentage missing values, percentage below detection limits (BDL) is also indicated. BDL corresponds to samples which were collected but whose concentrations were lower than the detection limits of the instrument/method by which the analytes were detected. In this table and all other summary statistics tables in the Supplemental

Conclusions

In response to the revised NAAQS and a general need to better understand the nature of fine PM over a National Park, a monitoring station was set-up at VVNP, Bhopal to measure PM2.5 mass and its chemical components. Samples were collected every other-day between January 2012 and December 2013. This study examined the temporal behavior of fine PM mass and its inorganic water soluble ionic constituents. The dependencies between major ionic species and their implications to neutralization of

Acknowledgments

The authors wish to gratefully acknowledge the financial support received from the Ministry of Earth Sciences (MoES), Government of India, to conduct this study through Project # MoES/16/09/10-RDEAS. Although this work was funded wholly by MoES, it does not necessarily reflect the views of the Ministry and no official endorsement should be inferred. The authors gratefully acknowledge the sanction and support received from the Director and all officials at Van Vihar National Park (VVNP), Bhopal

References (31)

  • D.K. Deshmukh et al.

    Water soluble ions in PM2.5 and PM1 aerosols in durg city, Chhattisgarh, India

    Aerosol Air Qual. Res.

    (2011)
  • R. Hillamo et al.

    Mass size distributions and precursor gas concentrations of major inorganic ions in Antarctic aerosol

    Int. J. Environ. Anal. Chem.

    (1998)
  • Y. Huang et al.

    A case study of the highly time-resolved evolution of aerosol chemical and optical properties in urban Shanghai, China

    Atmos. Chem. Phys.

    (2013)
  • N. Jain et al.

    Emission of air pollutants from crop residue burning in India

    Aerosol Air Qual. Res.

    (2014)
  • W.C. Keene et al.

    Sea-salt corrections and interpretation of constituent ratios in marine precipitation

    J. Geophys. Res.

    (1986)
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