Insights into Chemical Coupling among Acidic Gases, Ammonia and Secondary Inorganic Aerosols

Sailesh N Behera,Rajasekhar Balasubramanian,Raghu Betha

doi:10.4209/aaqr.2012.11.0328

Sailesh N Behera, Rajasekhar Balasubramanian + Show 1 more

Open Access

https://doi.org/10.4209/aaqr.2012.11.0328

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Abstract

This study has investigated the chemical association among acidic gases, ammonia and secondary inorganic aerosols based on hourly measurements in a tropical urban atmosphere. The 24 hr average concentrations of SO2, NH3, HONO, HNO3 and HCl were 21.77, 2.47, 1.73, 3.00 and 0.08 μg/m 3 , respectively while those of SO4 2– , NO3 – , Cl – , Na + , K + , NH4 + , Ca 2+ and Mg 2+ in PM2.5 were 4.41, 1.29, 0.28, 0.30, 0.32, 1.76, 0.14 and 0.07 μg/m 3 , respectively. The results of this study for SO2, NH3, HONO, HCl, SO4 2– and Cl – showed significant diurnal variations, whereas there was a lack of significant diurnal variations for HNO3, NO3 – , Na + , NH4 + , Ca 2+ and Mg 2+ . Analysis of the charge balance of ionic species indicated that sufficient NH3 was present most of the time to neutralize both H2SO4 and HNO3 to form (NH4)2SO4 and NH4NO3. The conversion of SO2 into SO4 2– and HNO3 into NO3 – was observed to be sensitive to changes in temperature and relative humidity, respectively. The study area experienced ambient relative humidity, which was higher than the estimated deliquescence relative humidity of NH4NO3 most of the time during the measurement period. As a result, the NH4NO3 formation was thermodynamically favorable during both daytime and nighttime. However, NH4Cl formation was not favored under ammonia-poor conditions. It was observed that biomass burning could trigger nitrate and chloride formation in the ambient air.

Highlights

Fine particulate matter (PM2.5) plays a significant role in atmospheric visibility reduction through the formation of haze, human health effects and climate change from the regional to global scale (Charlson and Heintzenberg, 1995; Vedal, 1997; IPCC, 2007)
The novelty of the work addressed in the present study is that we provide deep insights into the formation of SIA based on hourly observations of acidic gases, ammonia and particulate-phase water soluble inorganic ions in a tropical environment in Southeast Asia for the first time
Acidic gases (SO2, HONO, HNO3, hydrochloric acid (HCl)), ammonia (NH3) and water-soluble inorganic ions (SO42, NO3, Cl, Na+, K+, NH4HSO4 and (NH4)+, Ca2+ and Mg2+) in PM2.5 were analyzed in Singapore with a short-time interval (1 hr)

Summary

Introduction

Fine particulate matter (PM2.5) plays a significant role in atmospheric visibility reduction through the formation of haze, human health effects and climate change from the regional to global scale (Charlson and Heintzenberg, 1995; Vedal, 1997; IPCC, 2007). A significant portion of PM2.5 is formed in the atmosphere through chemical transformations of precursor gases such as nitrogen oxides (NOx), sulfur dioxide (SO2), and ammonia (NH3). This gas-to-particle conversion occurs either by condensation, which adds mass onto pre-existing aerosols, or by direct nucleation of these precursor gases (Baek and Aneja, 2004; Song et al, 2006). The major inorganic compounds formed through the gas-to-particle formation process are ammonium bisulfate (NH4HSO4), ammonium sulfate (NH4)2SO4, ammonium nitrate (NH4NO3) and ammonium chloride (NH4Cl). NH4HSO4 and (NH4)2SO4 are non-volatile in nature whereas NH4NO3 and NH4Cl are semi-volatile.

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