Source apportionment of gaseous Nitrophenols and their contribution to HONO formation in an urban area.

Nitrophenols (NPs) have significant impacts on human health, climate, and atmospheric chemistry. Despite numerous measurements of particulate NPs, still little is known about their gaseous atmospheric abundances, sources, and fate. Here, four gaseous NPs [2,4-dinitrophenol (2,4-DNP), 4-nitrophenol (4-NP), 2-nitrophenol (2-NP), and 2-Methyl-4-nitrophenol (2-Me-4-NP)] were continuously monitored during late Spring at an urban site in Houston, Texas. Among the four NPs, 4-NP showed the highest abundance, followed by 2-Me-4-NP, 2-NP, and 2,4-DNP with average concentrations of 1.07 ± 0.19 ppt, 0.47 ± 0.12 ppt, 0.41 ± 0.16 ppt, and 0.27 ± 0.09 ppt, respectively. The positive matrix factorization (PMF) model identified seven sources: industrial NPs, secondary formation, phenol sources, acetonitrile source, natural gas/crude oil, traffic, and petrochemical industries/oil refineries. A zero-dimensional photochemical box model was used to simulate the observed 2-NP and 2,4-DNP. A 50.0% and 70.0% jNO2 was found to be consistent with the measured 2-NP and 2,4-DNP. This yields a nitrous acid (HONO) production of 7.5 ± 2.5 ppt/h from 06:00 to 18:00 Central Standard Time (CST) from both NPs. An extrapolation including other known NPs suggests a maximum HONO formation of 13.8 ppt/h. The results of this study suggest that using PMF analysis supplemented by photochemical box model provides identification of the NPs sources and their atmospheric implication to HONO formation.

Ozone precursors and boundary layer meteorology before and during a severe ozone episode in Mexico city.

Volatile organic compounds (VOCs) data in conjunction with other inorganic pollutants, surface meteorological data and continuous measurement of the Planetary Boundary Layer height (PBLH) at an urban site in Mexico City were performed from 6 to 18 March 2016. Positive Matrix Factorization (PMF) identified four emission source factors of VOCs along with equivalent black carbon (eBC), gaseous pollutants (CO, NO, NO2, SO2, NH3) and ions (Na+, Mg2+, Ca2+, NO3-, NH4+): (1) secondary aerosol precursors, (2) evaporation and non-LPG fuel combustion, (3) geogenic source and (4) vehicle exhaust. Propylene Equivalent and Maximum Incremental Reactivity (MIR) methods identified isoprene and ethylene as the highest oxidant and O3 forming species. Pollutant data normalized to the variation of the PBLH revealed continued production of O3 precursors in the afternoon beyond the typical morning rush hour. In particular this could be observed during the second part of the measurement period (12-15 March) when a strong O3 episode occurred under weak wind and lower PBLH conditions compared to the preceding period (6-11 March) when well mixed conditions due to elevated daytime PBLH and strong advection led to overall reduced pollutant mixing ratios in the afternoon hours.

Measurement of nitrophenols in rain and air by two-dimensional liquid chromatography-chemically active liquid core waveguide spectrometry.

We report a novel system to analyze atmospheric nitrophenols (NPs). Rain or air sample extracts (1 mL) are preconcentrated on a narrow bore (2 mm) aliphatic anion exchanger. In the absence of strong retention of NPs exhibited by aromatic ion exchangers, retained NPs are eluted as a plug by injection of 100 microL of 0.1 M Na(2)SO(4) on to a short (2 x 50 mm) reverse phase C-18 column packed with 2.2 mum particles. The salt plug passes through the C-18 column unretained while the NPs are separated by an ammonium acetate buffered methanol-water eluent, compatible with mass spectrometry (MS). The eluted NPs are measured with a long path Teflon AF-based liquid core waveguide (0.15 x 1420 mm) illuminated by a 403 nm light emitting diode and detected by a monolithic photodiode-operational amplifier. The waveguide is rendered chemically active by suspending it over concentrated ammonia that permeates into the lumen. The NPs ionize to the yellow anion form (lambda(max) approximately 400 nm). The separation of 4-nitrophenol, 2,4-dinitrophenol, 2-methyl-4-nitrophenol, 3-methyl-4-nitrophenol, and 2-nitrophenol (these are the dominant NPs, typically in that order, in both rain and air of Houston and Arlington, TX, confirmed by tandem MS) takes just over 5 min with respective S/N = 3 limits of detection (LODs) of 60, 12, 30, 67, and 23 pg/mL compared to MS/MS LODs of 20, 49, 11, 20, and 210 pg/mL. Illustrative air and rain data are presented.