Nighttime chemical evolution of aerosol and trace gases in a power plant plume: Implications for secondary organic nitrate and organosulfate aerosol formation, NO₃ radical chemistry, and N₂O₅ heterogeneous hydrolysis

Abstract

[1] Nighttime chemical evolution of aerosol and trace gases in a coal-fired power plant plume was monitored with the Department of Energy Grumman Gulfstream-1 aircraft during the 2002 New England Air Quality Study field campaign. Quasi-Lagrangian sampling in the plume at increasing downwind distances and processing times was guided by a constant-volume balloon that was released near the power plant at sunset. While no evidence of fly ash particles was found, concentrations of particulate organics, sulfate, and nitrate were higher in the plume than in the background air. The enhanced sulfate concentrations were attributed to direct emissions of gaseous H 2 SO 4 , some of which had formed new particles as evidenced by enhanced concentrations of nucleation-mode particles in the plume. The aerosol species were internally mixed and the particles were acidic, suggesting that particulate nitrate was in the form of organic nitrate. The enhanced particulate organic and nitrate masses in the plume were inferred as secondary organic aerosol, which was possibly formed from NO 3 radical-initiated oxidation of isoprene and other trace organic gases in the presence of acidic sulfate particles. Microspectroscopic analysis of particle samples suggested that some sulfate was in the form of organosulfates. Microspectroscopy also revealed the presence of sp 2 hybridized C = C bonds, which decreased with increasing processing time in the plume, possibly because of heterogeneous chemistry on particulate organics. Constrained plume modeling analysis of the aircraft and tetroon observations showed that heterogeneous hydrolysis of N 2 O 5 was negligibly slow. These results have significant implications for several issues related to the impacts of power plant emissions on air quality and climate.Citation: Zaveri, R. A., et al. (2010), Nighttime chemical evolution of aerosol and trace gases in a power plant plume: Implications for secondary organic nitrate and organosulfate aerosol formation, NO 3 radical chemistry, and N 2 O 5 heterogeneous hydrolysis,

Photoacoustic optical properties at UV, VIS, and near IR wavelengths for laboratory generated and winter time ambient urban aerosols

“…NO 2 photolysis at 405 nm and shorter wavelengths prevents direct measurement of path extinction = photoacoustic absorption since some of the absorbed optical power goes into bond breaking rather than to heat. O 2 has been investigated as a calibration gas in the oxygen A band spectral region near 760 nm (oxygen A band, tunable laser) but in this wavelength range, gaseous light absorption involves significant relaxation processes that are mediated by water vapor (Gilles et al, 2010;Tian et al, 2009). In this case, the molecular physics of oxygen is very interesting, but the accuracy of using gas calibration for aerosol light absorption measurement is less assured.…”

“…Jacobson (1999) found that the nearly 50 % decline in UV radiation within the boundary layer (BL) in Los Angles was due to substantial UV absorption by nitrated and aromatic aerosols and gaseous species. A very recent study indicated nighttime formation of particulate organic nitrate and organosulfate species in coal-fired power plant plumes (Zaveri et al, 2010) that may also absorb UV radiation the following day.…”

Long-range pollution transport during the MILAGRO-2006 campaign: a case study of a major Mexico City outflow event using free-floating altitude-controlled balloons

“…Similar free-floating balloons have been used for many years to characterize transport and measure trajectories (e.g., Lally, 1967;Banta, 1976;Zak, 1983;Malaterre, 1993;Knudsen and Carver, 1994;Stohl, 1998;Businger et al, 1999;Johnson et al, 2000;Riddle et al, 2006;Mao et al, 2006;Zaveri et al, 2010a, b). These efforts have generally focused on tracking the horizontal motion of air masses or equivalently volumes of air that are sufficiently large to maintain their physical and chemical identity over a time period of interest.…”

Hydrolysis of Organonitrate Functional Groups in Aerosol Particles

“…Despite these model predictions, direct measurements of particle-phase ON concentrations in both laboratory and ambient studies are scarce due to limitations of measuring techniques and ON concentrations often must be inferred. For example, Zaveri et al (2010) inferred up to ∼0.4 µg m −3 of particulate ON (corresponding to <5% of total particulate mass) in a nocturnal power plant plume based on particle acidity and gasparticle equilibrium analysis of Aerodyne quadrupole aerosol mass spectrometer (Q-AMS) measurements. While aerosol mass spectroscopy is the most commonly employed technique for measuring the chemical composition of OM, it is not ideal for directly measuring ON concentrations (Farmer et al 2010).…”