Abstract. A four-channel thermal dissociation laser induced fluorescence (TD-LIF) instrument has been developed for simultaneous measurements of nitrogen dioxide (NO2), total peroxy nitrate (∑PNs), total alkyl nitrate (∑ANs) and nitric acid (HNO3). NO2 is measured directly by LIF at 532 nm, whereas organic nitrates and nitric acid are thermally dissociated at distinct temperatures in the inlet to form NO2, which is then measured by LIF. The concentrations of each dissociated species are derived by the differences in measured NO2 relative to the reference colder inlet channel. The TD-LIF was adapted to fly on board the UK Facility for Airborne Atmospheric Measurements (FAAM) BAe 146-301 atmospheric research aircraft in summer 2010, and to date has successfully flown in five field campaigns. This paper reports novel improvements in the TD-LIF instrumentations, including (1) the use of a single wavelength laser, which makes the system compact and relatively cheap; (2) the use of a single beam laser that allows easy alignment and optical stability against the vibrational aircraft environment; and (3) the optical assembly of four detection cells that allow simultaneous and fast (time resolution up to 0.1 s) measurements of NO2, ∑PNs, ∑ANs and HNO3. Laboratory-generated mixtures of PNs, ANs and HNO3 in zero air are converted into NO2 and used to fix the dissociation temperatures of each heated inlet to test the selectivity of the instrument and potential interferences due to recombination reactions of the dissociated products. The effectiveness of the TD-LIF was demonstrated during the RONOCO aircraft campaign (summer 2010). A chemiluminescence system that was measuring NO2 and a broadband cavity enhanced absorption spectrometer (BBCEAS) that was measuring one of the PNs (N2O5) were installed on the same aircraft during the campaign. The in-flight intercomparison of the new TD-LIF with the chemiluminescence system for NO2 measurements and the intercomparison between ∑PNs measured by the TD-LIF and N2O5 by the BBCEAS are used to assess the performance of the TD-LIF.
Aircraft observations of the lower troposphere above a megacity: alkyl nitrate and ozone chemistry, Atmospheric Environment (2014Environment ( ), doi: 10.1016Environment ( /j.atmosenv.2014 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. peroxides (H 2 O 2 , ROOH) altering the O 3 production. In the observations reported here, we found 39 that a strong ozone titration (∆O 3 = -16 ppb), due to a rapid increase of NO x (∆NO x = 27 ppb), 40 corresponds also to a high increase of ΣANs concentrations (∆ΣANs = 3 ppb), and quite stable 41 concentrations of HNO 3 and ΣPNs. Unexpectedly, compared with other megacities, the production 42 of ΣANs is similar to that of O x (O 3 + NO 2 ), suggesting that in the London plume, at least during 43 these observations, the formation of ΣANs effectively removes active NO x and hence reduces the 44 amount of O 3 production. In fact, we found that the ratio between the ozone production and the 45 alkyl nitrates production (observed) approximate the unity; on the contrary the calculated ratio is 7. 46In order to explain this discrepancy, we made sensitivity tests changing the alkyl nitrates branching 47 ratio for some VOCs and we investigated the impact of the unmeasured VOCs during the flight, 48founding that the calculated ratio decreases from 7 to 2 and that, in this condition, the major 49
Abstract. Total peroxy nitrate ( PN) concentrations have been measured using a thermal dissociation laser-induced fluorescence (TD-LIF) instrument during the BORTAS campaign, which focused on the impact of boreal biomass burning (BB) emissions on air quality in the Northern Hemisphere. The strong correlation observed between the PN concentrations and those of carbon monoxide (CO), a wellknown pyrogenic tracer, suggests the possible use of the PN concentrations as marker of the BB plumes. Two methods for the identification of BB plumes have been applied: (1) PN concentrations higher than 6 times the standard deviation above the background and (2) PN concentrations higher than the 99th percentile of the PNs measured during a background flight (B625); then we compared the percentage of BB plume selected using these methods with the percentage evaluated, applying the approaches usually used in literature. Moreover, adding the pressure threshold (∼ 750 hPa) as ancillary parameter to PNs, hydrogen cyanide (HCN) and CO, the BB plume identification is improved. A recurrent artificial neural network (ANN) model was adapted to simulate the concentrations of PNs and HCN, including nitrogen oxide (NO), acetonitrile (CH 3 CN), CO, ozone (O 3 ) and atmospheric pressure as input parameters, to verify the specific role of these input data to better identify BB plumes.
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