Abstract
Nitrophenols, hazardous environmental pollutants, react promptly with atmospheric oxidants such as hydroxyl or nitrate radicals. This work aimed to estimate how fast nitrophenols are removed from the atmosphere by the aqueous-phase reactions with sulfate radical-anions. The reversed-rates method was applied to determine the relative rate constants for reactions of 2-nitrophenol, 3-nitrophenol, 4-nitrophenol, 2,4-dinitrophenol, and 2,4,6-trinitrophenol with sulfate radical-anions generated by the autoxidation of sodium sulfite catalyzed by iron(III) cations at ~298 K. The constants determined were: 9.08 × 108, 1.72 × 109, 6.60 × 108, 2.86 × 108, and 7.10 × 107 M−1 s−1, respectively. These values correlated linearly with the sums of Brown substituent coefficients and with the relative strength of the O–H bond of the respective nitrophenols. Rough estimation showed that the gas-phase reactions of 2-nitrophenol with hydroxyl or nitrate radicals dominated over the aqueous-phase reaction with sulfate radical-anions in deliquescent aerosol and haze water. In clouds, rains, and haze water, the aqueous-phase reaction of 2-nitrophenol with sulfate radical-anions dominated, provided the concentration of the radical-anions was not smaller than that of the hydroxyl or nitrate radicals. The results presented may be also interesting for designers of advanced oxidation processes for the removal of nitrophenol.
Highlights
Nitrophenols are well known environmental trace compounds and pollutants [1,2], which have been detected in various environmental matrices including air [3,4,5,6], rainwater [3,7,8,9], cloud water [10], fog [10,11], snow [1], atmospheric aerosol [4,5,6,12,13,14,15,16,17,18,19,20,21,22,23,24,25], soils [26,27], and surface waters [10,28,29,30,31,32]
They originate from many anthropogenic and natural sources including: the incineration of wastes [33], industrial chemical processes [34], combustion of coal and biomass as well as vehicle and aviation fuels [35,36,37], degradation of pesticides [34,38,39], release of wood preservatives [34], and atmospheric chemical reactions. 4-nitrophenol (4-NP) and 2,4-dinitrophenol (2,4-DNP), along with sugar anhydrides such as levoglucosan, serve as markers of biomass burning in ambient aerosol [40,41,42,43]
This work was aimed at elucidating how fast nitrophenols are removed from the atmospheric waters by reaction with sulfate radical-anions, which are important atmospheric oxidants known to react fast with numerous atmospheric pollutants [77,78,79,80,81,82,83]
Summary
Nitrophenols are well known environmental trace compounds and pollutants [1,2], which have been detected in various environmental matrices including air [3,4,5,6], rainwater [3,7,8,9], cloud water [10], fog [10,11], snow [1], atmospheric aerosol [4,5,6,12,13,14,15,16,17,18,19,20,21,22,23,24,25], soils [26,27], and surface waters [10,28,29,30,31,32] They originate from many anthropogenic and natural sources including: the incineration of wastes [33], industrial chemical processes [34], combustion of coal and biomass as well as vehicle and aviation fuels [35,36,37], degradation of pesticides [34,38,39], release of wood preservatives [34], and atmospheric chemical reactions. The possible pathways include oxidation of phenols with NO2 and OH or NO3 radicals [46], Atmosphere 2019, 10, 795; doi:10.3390/atmos10120795 www.mdpi.com/journal/atmosphere
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