[1] We employed a fast response thermal dissociation-chemical ionization mass spectrometer (TD-CIMS) system to measure eddy covariance fluxes of peroxyacetyl nitrate (PAN), peroxypropionyl nitrate (PPN) and peroxymethacryloyl nitrate (MPAN). Average PAN deposition velocities, V d (PAN), showed a daytime maximum of $10.0 mm s À1 ; however, deposition did not cease during nighttime periods. V d (PAN) was highly variable at night and increased when canopy elements were wet from either precipitation or dew formation. Diel patterns of deposition velocity of MPAN and PPN were similar to that of PAN. These results suggest that deposition of PAN, at least to coniferous forest canopies, is much faster than predicted with current deposition algorithms. Although deposition of PAN is unlikely to compete with thermal dissociation during warm summer periods, it will likely play an important role in removing PAN from the atmosphere in colder regions or during winter. The fate of PAN at the surface and within the plants remains unknown, but may present a previously ignored source of nitrogen to ecosystems.

[1] Emission of bromine from sea-salt aerosol, frost flowers, ice leads, and snow results in the nearly complete removal of surface ozone during Arctic spring. Regions of enhanced total column BrO observed by satellites have traditionally been associated with these emissions. However, airborne measurements of BrO and O 3 within the convective boundary layer (CBL) during the ARCTAS and ARCPAC field campaigns at times bear little relation to enhanced column BrO. We show that the locations of numerous satellite BrO "hotspots" during Arctic spring are consistent with observations of total column ozone and tropopause height, suggesting a stratospheric origin to these regions of elevated BrO. Tropospheric enhancements of BrO large enough to affect the column abundance are also observed, with important contributions originating from above the CBL. Closure of the budget for total column BrO, albeit with significant uncertainty, is achieved by summing observed tropospheric partial columns with calculated stratospheric partial columns provided that natural, short-lived biogenic bromocarbons supply between 5 and 10 ppt of bromine to the Arctic lowermost stratosphere. Proper understanding of bromine and its effects on atmospheric composition requires accurate treatment of geographic variations in column BrO originating from both the stratosphere and troposphere.

Abstract. In situ measurements of ozone, photochemically active bromine compounds, and other trace gases over the Arctic Ocean in April 2008 are used to examine the chemistry and geographical extent of ozone depletion in the arctic marine boundary layer (MBL). Data were obtained from the NOAA WP-3D aircraft during the Aerosol, Radiation, and Cloud Processes affecting Arctic Climate (ARCPAC) study and the NASA DC-8 aircraft during the Arctic Research of the Composition of the Troposphere from Aircraft and Satellites (ARCTAS) study. Fast (1 s) and sensitive (detection limits at the low pptv level) measurements of BrCl and BrO were obtained from three different chemical ionization mass spectrometer (CIMS) instruments, and soluble bromide was measured with a mist chamber. The CIMS instruments also detected Br 2 . Subsequent laboratory studies showed that HOBr rapidly converts to Br 2 on the Teflon instrument inlets. This detected Br 2 is identified as active bromine and represents a lower limit of the sum HOBr + Br 2 . The measured active bromine is shown to likely be HOBr during daytime flights in the arctic. In the MBL over the Arctic Ocean, soluble bromide and active bromine were consistently elevated and ozone was depleted. Ozone depletion and active bromine enhancement were confined to the MBL that was capped by a temperature inversion at 200-500 m altitude. In ozonedepleted air, BrO rarely exceeded 10 pptv and was always substantially lower than soluble bromide that was as high as 40 pptv. BrCl was rarely enhanced above the 2 pptv detection limit, either in the MBL, over Alaska, or in the arctic free troposphere.

4) Orban, M.; Kijrb, E. K b b , E.; Noyes, R. M. J. Am. Chem. Soc. 1972, 94, Trans. 1992,88, 917. S = 2 k~l / k~6 / &~3 &~ = 9.52 x 10" b = 2kB6kB9[R]/k~lkW[BrOS-] = 0.545 K 3 k~z / k~l = 1.6 6 = k~l / 2 k~6 = 3.33 x r = k~i k~a / k~k~s = 0.101 Q = 2 k~s k~/ k~, ' = 0.0101 0 = kB,/kB6 = 1.667 x lo3 B = k~3 / 2 k~6 = 500 T,,, = kW[Br03-]trea = 3.91t,/s Repistry No. BrO,-, 15541-45-4; gallic acid, 149-91-7; ferroin, 14708-99-7.Timaresolved fluorescmCe detection Of Cl(9j) following 266-nm laser flash photd~is Of Cl~cO/CH$CH~(DMS)/N~ mixtures has been employed to study the kinetics of the title reaction over the temperature and pressure ranges 240-421 K and 3-700 Torr. The reaction is found to be very fast, occumng on essentially every C1(2PJ) + DMS encounter. The reaction rate increases with decreasing temperature and shows a significant pressure dependence. At 297 K, for example, the rate coefficient increases from a low-pressure limit value of approximately 1.8 X cm3 molecule-' s-' to a value of (3.3 f 0.5) X cm3 molecule-' s-l at P = 700 Torr. A few experiments were carried out with CD3SCD3 or C2H5SC2Hs replacing DMS as the sulfide reactant; within experimental uncertainty, no dependence of the rate coefficient on the identity of the sulfide reactant was observed. In a separate study, time-resolved tunable diode laser spectroscopic detection of HCl has been coupled with 248-nm laser flash photolysis of Cl&O/DMS/COz/Nz mixtures to measure the HCl product yield from the title reaction as a function of pressure at T = 297 K. The HCl yield approaches unity as P -0 but decreases with increasing pressure to a value of -0.5 at P = 203 Torr. The yield experiments demonstrate that hydrogen abstraction is the dominant reaction mechanism in the low-pressure limit. With increasing pressure, stabilization of a (CH3)gCI adduct apparently becomes competitive with the hydrogen abstraction pathway. The fate of the stabilized adduct remains highly uncertain, although it clearly does not dissociate to Cl(9J) or HCl on the time scale of our experiments (several milliseconds). The potential role of the title reaction in marine atmospheric chemistry is discussed.

Abstract. We analyze summertime photochemistry near the surface in Beijing, China, using a 1-D photochemical model (Regional chEmical and trAnsport Model, REAM-1D) constrained by in situ observations, focusing on the budgets of ROx (OH + HO2 + RO2) radicals and O3 formation. While the modeling analysis focuses on near-surface photochemical budgets, the implications for the budget of O3 in the planetary boundary layer are also discussed. In terms of daytime average, the total ROx primary production rate near the surface in Beijing is 6.6 ppbv per hour (ppbv h−1, among the highest found in urban atmospheres. The largest primary ROx source in Beijing is photolysis of oxygenated volatile organic compounds (OVOCs), which produces HO2 and RO2 at 2.5 ppbv h−1 and 1.7 ppbv h−1, respectively. Photolysis of excess HONO from an unknown heterogeneous source is the predominant primary OH source at 2.2 ppbv h−1, much larger than that of O1D+H2O (0.4 ppbv h−1). The largest ROx sink is via OH + NO2 reaction (1.6 ppbv h−1), followed by formation of RO2NO2 (1.0 ppbv h−1) and RONO2 (0.7 ppbv h−1). Due to the large aerosol surface area, aerosol uptake of HO2 appears to be another important radical sink, although the estimate of its magnitude is highly variable depending on the uptake coefficient value used. The daytime average O3 production and loss rates near the surface are 32 ppbv h−1 and 6.2 ppbv h−1, respectively. Assuming NO2 to be the source of excess HONO, the NO2 to HONO transformation leads to considerable O3 loss and reduction of its lifetime. Our observation-constrained modeling analysis suggests that oxidation of VOCs (especially aromatics) and heterogeneous reactions (e.g. HONO formation and aerosol uptake HO2) play potentially critical roles in the primary radical budget and O3 formation in Beijing. One important ramification is that O3 production is neither NOx nor VOC limited, but in a transition regime where reduction of either NOx or VOCs could result in reduction of O3 production. The transition regime implies more flexibility in the O3 control strategies than a binary system of either NOx or VOC limited regime. The co-benefit of concurrent reduction of both NOx and VOCs in reducing column O3 production integrated in the planetary boundary layer is significant. Further research on the spatial extent of the transition regime over the polluted eastern China is critically important for controlling regional O3 pollution.