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Tracer flux ratio methodology was applied to airborne measurements to quantify methane (CH4) emissions from two dairy farms in central California during the summer. An aircraft flew around the perimeter of each farm measuring downwind enhancements of CH4 and a tracer species released from the ground at a known rate. Estimates of CH4 emission rates from this analysis were determined for whole sites and major sources within a site (animal housing and liquid manure lagoons). Whole-site CH4 flux rates for each farm, Dairy 1 (6108±821kgCH4dg-1, 95% confidence interval) and Dairy 2 (4018±456kgCH4dg-1, 95% confidence interval), closely resembled findings by established methods: ground-based tracer flux ratio and mass balance. Individual source emission rates indicate a greater fraction of the whole-site emissions come from liquid manure management than animal housing activity, similar to bottom-up estimates. Despite differences in altitude, we observed that the tracer release method gave consistent results when using ground or air platforms..

Nitryl chloride (ClNO2) is a radical reservoir species that releases chlorine radicals upon photolysis. An integrated analysis of the impact of ClNO2 on regional photochemistry in the Seoul metropolitan area (SMA) during the Korea-United States Air Quality Study (KORUS-AQ) 2016 field campaign is presented. Comprehensive multiplatform observations were conducted aboard the NASA DC-8 and at two ground sites (Olympic Park, OP; Taehwa Research Forest, TRF), representing an urbanized area and a forested suburban region, respectively. Positive correlations between daytime Cl2 and ClNO2 were observed at both sites, the slope of which was dependent on O3 levels. The possible mechanisms are explored through box model simulations constrained with observations. The overall diurnal variations in ClNO2 at both sites appeared similar but the nighttime variations were systematically different. For about half of the observation days at the OP site the level of ClNO2 increased at sunset but rapidly decreased at around midnight. On the other hand, high levels were observed throughout the night at the TRF site. Significant levels of ClNO2 were observed at both sites for 4-5 h after sunrise. Airborne observations, box model calculations, and back-trajectory analysis consistently show that these high levels of ClNO2 in the morning are likely from vertical or horizontal transport of air masses from the west. Box model results show that chlorine-radical-initiated chemistry can impact the regional photochemistry by elevating net chemical production rates of ozone by 25% in the morning.

Abstract. Nitryl chloride (ClNO2) is a radical reservoir species that releases chlorine radicals upon photolysis. An integrated analysis of the impact of ClNO2 on regional photochemistry in the Seoul Metropolitan Area (SMA) during the Korean-United States-Air Quality (KORUS-AQ) 2016 field campaign is presented. Comprehensive multiplatform observations were conducted aboard the NASA DC-8 and at two ground sites (Olympic Park, OP; Taehwa Research Forest, TRF), representing an urbanized area and a forested region downwind, respectively. The overall diurnal variations of ClNO2 in both sites appeared similar but the night time variation were systematically different. For about half of the observation days at the OP site the level of ClNO2 increased at sunset but rapidly decreased at around midnight. On the other hand, high levels were sustained throughout the night at the TRF site. Significant levels of ClNO2 were sustained at both sites for 4–5 hours after sunrise. Airborne observations, box model calculations, and back trajectory analysis consistently show that this high levels of ClNO2 in the morning is likely due to the transport of air masses within the boundary layer. Box model results show that chlorine radical initiated chemistry can impact the regional photochemistry by elevating net ozone production rate up to ~ 25 % in the morning.

Black carbon (BC) and light-absorbing organic carbon (brown carbon, BrC) play key roles in warming the atmosphere, but the magnitude of their effects remains highly uncertain. Theoretical modelling and laboratory experiments demonstrate that coatings on BC can enhance BC's light absorption, therefore many climate models simply assume enhanced BC absorption by a factor of ∼1.5. However, recent field observations show negligible absorption enhancement, implying models may overestimate BC's warming. Here we report direct evidence of substantial field-measured BC absorption enhancement, with the magnitude strongly depending on BC coating amount. Increases in BC coating result from a combination of changing sources and photochemical aging processes. When the influence of BrC is accounted for, observationally constrained model calculations of the BC absorption enhancement can be reconciled with the observations. We conclude that the influence of coatings on BC absorption should be treated as a source and regionally specific parameter in climate models.

Wildfires have become an increasingly important source of organic gases and particulate matter in the western United States. A large fraction of organic particulate matter emitted in wildfires is semivolatile, and the oxidation of organic gases in smoke can form lower volatility products that then condense on smoke particulates. In this research, we measured the gas- and particle-phase concentrations of semivolatile organic compounds (SVOCs) during the 2017 Northern California wildfires in a downwind urban area, using the Semivolatile Thermal-Desorption Aerosol Gas Chromatography (SV-TAG), and measured SVOCs in a rural site affected by biomass burning using the comprehensive TAG (cTAG) in Idaho in 2018. Commonly used biomass burning markers such as levoglucosan, mannosan and nitrocatechols were found to stay predominantly in the particle phase, even when the ambient OA was relatively low. The phase partitioning of SVOCs is observed to be dependent on their saturation vapor pressure, while the absorptive equilibrium model underpredicts the particle-phase fraction of most of the compounds measured. Wildfire organic aerosol enhanced the condensation of polar compounds into the particle phase but not some nonpolar compounds, such as polycyclic aromatic hydrocarbons. [ABSTRACT FROM AUTHOR]

An Aerodyne tunable infrared laser direct absorption spectrometer with a multipass cell with a 413 m pathlength for the detection of ethylene oxide (EtO) is presented (TILDAS-FD-EtO). This monitor achieves precisions of <75 ppt or <0.075 ppb s -1 and <20 ppt in 100 s (1 σ). We demonstrate precisions averaging down to 4 ppt h -1 (1 σ precision) when operated with frequent humidity-matched zeroes. A months-long record of 2022 ambient concentrations at a site in the eastern United States is presented. Average ambient EtO concentration is on the order of 18 ppt (22 ppt standard deviation, SD). Enhancement events of EtO lasting a few hours are observed, with peaks as high as 600 ppt. Back-trajectory simulations suggest an EtO source nearly 35 km away. This source along with another are confirmed as emitters through mobile near-source measurements, with downwind concentrations in the 0.5 to 700 ppb range depending on source identity and distance downwind. [ABSTRACT FROM AUTHOR]

The largest inorganic, gas-phase reservoir of chlorine atoms in the atmosphere is hydrogen chloride (HCl), but challenges in quantitative sampling of this compound cause difficulties for obtaining high-quality, high-frequency measurements. In this work, tunable infrared laser direct absorption spectroscopy (TILDAS) was demonstrated to be a superior optical method for sensitive, in situ detection of HCl at the 2925.89645 cm -1 absorption line using a 3 µ m inter-band cascade laser. The instrument has an effective path length of 204 m, 1 Hz precision of 7–8 pptv, and 3 σ limit of detection ranging from 21 to 24 pptv. For longer averaging times, the highest precision obtained was 0.5 pptv with a 3 σ limit of detection of 1.6 pptv at 2.4 min. HCl-TILDAS was also shown to have high accuracy when compared with a certified gas cylinder, yielding a linear slope within the expected 5 % tolerance of the reported cylinder concentration (slope = 0.964 ± 0.008). The use of heated inlet lines and active chemical passivation greatly improve the instrument response times to changes in HCl mixing ratios, with minimum 90 % response times ranging from 1.2 to 4.4 s depending on inlet flow rate. However, these response times lengthened at relative humidities >50 %, conditions under which HCl concentration standards were found to elicit a significantly lower response (-5.8 %). The addition of high concentrations of gas-phase nitric acid (>3.0 ppbv) were found to increase HCl signal (<10 %), likely due to acid displacement with HCl or particulate chloride adsorbed to inlet surfaces. The equilibrium model ISORROPIA suggested a potential of particulate chloride partitioning into HCl gas within the heated inlet system if allowed to thermally equilibrate, but field results did not demonstrate a clear relationship between particulate chloride and HCl signal obtained with a denuder installed on the inlet. [ABSTRACT FROM AUTHOR]

ABSTRACT Aerosol mass spectrometer (AMS) measurements are used to characterize the evolution of exhaust particulate matter (PM) properties near and downwind of vehicle sources. The AMS provides time-resolved chemically speciated [...]

The characterization of volatile and nonvolatile particle materials present in gas turbine exhaust is critical for accurate estimation of the potential impacts of airport activities on local air quality, atmospheric processes, and climate change. Two field campaigns were performed to collect an extensive set of particle and gaseous emission data for on-wing gas turbine engines. The tests included CFM56, RB211-535E4-B, AE3007, PW4158, and CJ610 engines, providing the opportunity to compare emissions from a wide range of engine technologies. Here we report mass, number, composition, and size data .for the nonvolatile (soot) and volatile particles present in engine exhaust. For all engines, soot emissions ([EI.sub.m]-soot) are greater at climbout (85% power) and takeoff (100% ) power than idle (4% or 7%) and approach (30%). At the engine exit plane, soot is the only type of particle detected. For exhaust sampled downwind (15-50 m) and diluted by ambient air, total particle number emissions ([EI.sub.n]-total) increases by about one or two orders of magnitude relative to the engine exit plane, and the increase is driven by volatile particles that have freshly nucleated in the cooling exhaust gas both in the free atmosphere and in the extractive sample lines. Fuel sulfur content is the determining factor for nucleation of new particles in the cooling exhaust gases. Compositional analysis indicates that the volatile particles consist of sulfate and organic materials ([EI.sub.m-]sulfate and [EI.sub.m]-organic). We estimate a lower bound S[IV] to S[VI] conversion efficiency of (0. 08 [+ or -] 0.01)%, independent of engine technology. Measurements of Elm-organic ranged from about 0.1 mg [kg.sup.-1] to 40 mg [kg.sup.-1]. Lubrication oil was present in particles emitted by all engines and accounted for over 90% of the particulate organic mass under some conditions. The products of incomplete combustion are a likely source of the remaining volatile organic particle material. [DOI: 10.1115/1.4000132]

The potential human health and environmental impacts of aircraft gas turbine engine emissions during normal airport operation are issues of growing concern. During the JETS/Aircraft Particle Emissions eXperiment(APEX)-2 and APEX-3 field campaigns, we performed an extensive series of gas phase and particulate emissions measurements of on-wing gas turbine engines. In all, nine different CFM56 style engines (including both CFM56-3BI and -7B22 models) and seven additional engines (two RB211-535E4-B engines, three AE3007 engines, one PW4158, and one CJ6108A) were studied to evaluate engine-to-engine variability. Specific gas-phase measurements include N[O.sub.2], NO, and total N[O.sub.x], HCHO, [C.sub.2][H.sub.4], CO, and a range of volatile organic compounds (e.g., benzene, styrene, toluene, naphthalene). A number of broad conclusions can be made based on the gas-phase data set: (1)field measurements of gas-phase emission indices (EIs) are generally consistent with 1CAO certification values; (2) speciation of gas phase N[O.sub.x] between NO and N[O.sub.2] is reproducible for different engine types and favors N[O.sub.2] at low power (and low fuel flow rate) and NO at high power (high fuel flow rate); (3) emission indices of gas-phase organic compounds and CO decrease rapidly with increasing fuel flow rate; (4) plotting EI-CO or volatile organic compound Els against fuel flow rate collapses much of the variability between the different engines, with one exception (AE3007); (5) HCHO, ethylene, acetaldehyde, and propene are the most abundant volatile organic compounds present in the exhaust gases that we can detect, independent of engine technology differences. Empirical correlations accurate to within 30% and based on the publicly available engine parameters are presented for estimating El-N[O.sub.x] and EI-N[O.sub.2]. Engine-to-engine variability, unavailability of combustor input conditions, changing ambient temperatures, and complex reaction dynamics limit the accuracy of global correlations for CO or volatile organic compound EIs. [DOI: 10.1115/1.4000131 ]

The largest inorganic, gas phase reservoir of chlorine atoms in the atmosphere is hydrogen chloride (HCl), but the challenges in quantitative sampling of this compound cause difficulties for obtaining high-quality, high-frequency measurements. In this work, tunable infrared laser direct absorption spectroscopy (TILDAS) was demonstrated to be a superior optical method for sensitive, in situ detection of HCl at the 2925.89645 cm-1 absorption line using a 3 μm interband cascade laser. The instrument has an effective path length of 204 m, 1 Hz precision of 7-8 pptv, and 3σ limit of detection ranging from 21-24 pptv. For longer averaging times, the highest precision obtained was 0.5 pptv and 3σ limit of detection of 1.6 pptv at 2.4 minutes. HCl TILDAS was also shown to have high accuracy when compared with a certified gas cylinder, yielding a linear slope within the expected 5% tolerance of the reported cylinder concentration (slope = 0.964 ± 0.008). The use of heated inlet lines and active chemical passivation greatly improve the instrument response times to changes in HCl mixing ratios, with minimum 90% response times ranging from 1.2 - 4.4 s, depending on inlet flow rate. However, these response times lengthened at relative humidities > 50%, conditions under which HCl concentration standards were found to elicit a significantly lower response (-5.8%). The addition of high concentrations of gas phase nitric acid (> 4.0 ppbv) were found to increase HCl signal (< 10%), likely due to acid displacement with HCl or particulate chloride adsorbed to inlet surfaces. The equilibrium model ISORROPIA suggested a potential of particulate chloride partitioning into HCl gas within the heated inlet system if allowed to thermally equilibrate, but field results did not demonstrate a clear relationship between particulate chloride and HCl signal obtained with a denuder installed on the inlet. [ABSTRACT FROM AUTHOR]

An Aerodyne Tunable Infrared Direct Absorption Spectrometer with 413 meter cell for the detection of ethylene oxide (EtO) is presented (TILDAS-FD-EtO). This monitor achieves precisions of <75 ppt or <0.075 ppb in 1 second and < 20 ppt in 100 seconds (1-sigma). We demonstrate precisions averaging down to 4 ppt in an hour (1-sigma precision) when operated with frequent humidity-matched zeroes. A months-long record of 2022 ambient concentrations at a site in the Eastern United States is presented. Average ambient EtO concentration is on the order of 18 ppt (22 ppt standard deviation). Enhancement events of EtO lasting a few hours are observed, with peaks as high as 600 ppt. Back trajectory simulations suggest an EtO source nearly 35 km away. This source along with another are confirmed as emitters through mobile near-source measurements, with downwind concentrations in the 0.5 ppb to 700 ppb range depending on source identity and distance downwind. [ABSTRACT FROM AUTHOR]

ABSTRACT We demonstrate the use of an aldehyde scrubber system to resolve isobaric aldehyde/alkene interferences in a proton transfer reaction mass spectrometer (PTR-MS) by selectively removing the aldehydes from the [...]

We present initial results obtained from an optical absorption sensor for the monitoring of ambient atmospheric nitrogen dioxide concentrations (0-200 ppb). This sensor utilizes cavity attenuated phase shift spectroscopy, a technology related to cavity ringdown spectroscopy. A modulated broadband incoherent light source (a 430-nm LED) is coupled to an optically resonant cavity formed by two high-reflectivity mirrors. The presence of N[O.sub.2] in the cell causes a phase shift in the signal received by a photodetector that is proportional to the N[O.sub.2] concentration. The sensor, which employed a 0.5-m cell, was shown to have a sensitivity of 0.3 ppb in the photon (shot) noise limit. Improvements in the optical coupling of the LED to the resonant cavity would allow the sensor to reach this limit with integration times of 10 s or less (corresponding to a noise equivalent absorption coefficient of < 1 x 10 s [cm.sup.-1] [Hz.sup.1/2]). Over a 2-day-long period of ambient atmospheric monitoring, a comparison of the sensor with an extremely accurate and precise tunable diode laser-based absorption spectrometer showed that the CAPS-based instrument was able to reliably and quantitatively measure both large and small fluctuations in the ambient nitrogen dioxide concentration.

The rate constant for the reaction of HO2 with O3 was measured using a turbulent flow reactor with tunable diode laser absorption detection of HO2. The results demonstrate that the catalytic destruction of lower stratospheric O3 by HOx radicals (OH and HO2) would proceed faster.