Observations of gas-phase products from the nitrate radical-initiated oxidation of four monoterpenes

Chemical ionization mass spectrometry with nitrate reagent ion (NO3− CIMS) was used to investigate the products of nitrate radical (NO3) initiated oxidation of four monoterpenes in laboratory chamber experiments. α-Pinene, β-pinene, Δ-3-carene, and α-thujene were studied. The major gas-phase species produced in each system were distinctly different, showing the effect of monoterpene structure on the oxidation mechanism and further elucidated the contributions of these species to particle formation and growth. By comparing groupings of products based on ratios of elements in the general formula CwHxNyOz, the relative importance of specific mechanistic pathways (fragmentation, termination, radical rearrangement) can be assessed for each system. Additionally, the measured time series of the highly oxidized reaction products provide insights into the ratio of relative production and loss rates of the high molecular weight products of the Δ-3-carene system. Measured effective O : C ratio of reaction products were anti-correlated to new particle formation intensity and number concentration for each system; however, monomer : dimer ratio of products was positively correlated. Gas phase yields of oxidation products measured by NO3− CIMS correlated with particle number concentrations for each monoterpene system, with the exception of α-thujene, which produced a considerable amount of low volatility products but no particles. Species-resolved wall loss was measured with NO3− CIMS and found to be highly variable among oxidized reaction products in our stainless steel chamber.

Rational Approach to Assess the Effect of Corrosion on Stiffened Panel Buckling and Ultimate Capacity

During the annual In-Service Inspection of a spar hull, several regions of pitting corrosion on the upper portion of the north and south moon pool external wall plating were identified. The moon pool walls are constructed as typical stiffened panel structures. Visual, ultrasonic (UT), and pulsed eddy current (PEC) inspections indicated regions of corrosion with roughly 40% to 70% averaged localized wall loss. This paper discusses the analytical assessment of the structure to determine the effect of the corrosion on the structural integrity of the moon pool wall and any similar structural panel. To determine the impact of corrosion on the stiffened panel integrity, a finite element (FE) based analysis approach is used to perform a comparative assessment of the "as-built" and "corroded" configuration of the moon pool wall. The nominal plate and stiffener thicknesses are modeled in the "as-built" configuration; whereas, the measured plate thickness from the inspection is modeled in the "corroded" configuration. The structure is subjected to design loads based on the storm damaged design condition. The analysis is performed by uniformly increasing the applied loads until failure occurs, maintaining a constant ratio between the nominal loads. Two different analyses are performed as a part of the strength assessment: (1) a linear-elastic eigenvalue analysis to estimate the elastic buckling capacity and mode shapes of the structure and (2) an elastic-plastic post-buckling analysis to estimate the ultimate capacity of the structure. In addition, the results from the linear-elastic eigenvalue analysis are compared to the results from analytical buckling calculations. The analysis results indicate that the corrosion reduces the elastic plate buckling capacity significantly. However, the overall capacity of the stiffened panel is not significantly reduced. Therefore, from a global strength perspective, the stiffened panel remains acceptable in its corroded condition. The upper portion of the moon pool wall is typically fatigue insensitive in spars. Therefore, the effect of the corrosion wall loss on the fatigue performance was not assessed. Since there is limited guidance in design and assessment codes for assessing corroded stiffened panels, this approach can be used to address future stiffened panel corrosion wall loss. In addition, this method allows for inclusion of future corrosion allowance, if applicable. Determining the capacity of corroded panels using FEA-based numerical methods, like those described in this paper, allows the operators to manage their risks, repair costs, and inspection frequency by determining the actual capacity of the damaged components. This allows the operators to determine the appropriate mitigation measures based on a quantitative risk calculation.

Influence of biomass burning vapor wall loss correction on modeling organic aerosols in Europe by CAMx v6.50

Increasing evidence from experimental studies suggests that the losses of semi-volatile vapors to chamber walls could be responsible for the underestimation of organic aerosol (OA) in air quality models that use parameters obtained from chamber experiments. In this study, a box model with a volatility basis set (VBS) scheme was developed, and the secondary organic aerosol (SOA) yields with vapor wall loss correction were optimized by a genetic algorithm based on advanced chamber experimental data for biomass burning. The vapor wall loss correction increases the SOA yields by a factor of 1.9–4.9 and leads to better agreement with measured OA for 14 chamber experiments under different temperatures and emission loads. To investigate the influence of vapor wall loss correction on regional OA simulations, the optimized parameterizations (SOA yields, emissions of intermediate-volatility organic compounds from biomass burning, and enthalpy of vaporization) were implemented in the regional air quality model CAMx (Comprehensive Air Quality Model with extensions). The model results from the VBS schemes with standard (VBS_BASE) and vapor-wall-loss-corrected parameters (VBS_WLS), as well as the traditional two-product approach, were compared and evaluated by OA measurements from five Aerodyne aerosol chemical speciation monitor (ACSM) or aerosol mass spectrometer (AMS) stations in the winter of 2011. An additional reference scenario, VBS_noWLS, was also developed using the same parameterization as VBS_WLS except for the SOA yields, which were optimized by assuming there is no vapor wall loss. The VBS_WLS generally shows the best performance for predicting OA among all OA schemes and reduces the mean fractional bias from −72.9 % (VBS_BASE) to −1.6 % for the winter OA. In Europe, the VBS_WLS produces the highest domain average OA in winter (2.3 µg m−3), which is 106.6 % and 26.2 % higher than VBS_BASE and VBS_noWLS, respectively. Compared to VBS_noWLS, VBS_WLS leads to an increase in SOA by up to ∼80 % (in the Balkans). VBS_WLS also leads to better agreement between the modeled SOA fraction in OA (fSOA) and the estimated values in the literature. The substantial influence of vapor wall loss correction on modeled OA in Europe highlights the importance of further improvements in parameterizations based on laboratory studies for a wider range of chamber conditions and field observations with higher spatial and temporal coverage.

High Resolution Acoustic Imaging of Plug Related Casing Damage in Hydraulically Fractured Horizontal Wells

While assessing post-hydraulic-fracture perforation growth using solid-state, high- resolution acoustic imaging tools, it was noted that plug failures were occurring at a high frequency. Though plug failures can be observed from hydraulic fracture surface pressure and flowrate data, the aggregate frequency, causes, and severity of the resulting erosional damage at plug locations was not previously well understood and highly speculative. The sub-millimetric three-dimensional imagery generated from high resolution solid-state acoustic tools significantly improved the industry's awareness of plug failure frequency, mechanisms of failure, and the resulting impact to stimulation efficiency. These acoustic tools helped to uncover the causes and explore possible solutions to failing plugs. This paper presents aggregate data encompassing casing wall loss at over 2700 plug locations and presents emerging trends that appear across the broader dataset. In addition, this paper showcases the usage of high-resolution acoustic imaging in two operator-specific case studies.

Molecular composition and volatility of multi-generation products formed from isoprene oxidation by nitrate radical

Isoprene oxidation by nitrate radical (NO3) is a potentially important source of secondary organic aerosol (SOA). It is suggested that the second or later-generation products are the more substantial contributors to SOA. However, there are few studies investigating the multi-generation chemistry of isoprene-NO3 reaction, and information about the volatility of different isoprene nitrates, which is essential to evaluate their potential to form SOA and determine their atmospheric fate, is rare. In this work, we studied the reaction between isoprene and NO3 in the SAPHIR chamber (Jülich) under near atmospheric conditions. Various oxidation products were measured by a high-resolution time-of-flight chemical ionization mass spectrometer using Br− as the reagent ion. They are grouped into monomers (C4- and C5-products), and dimers (C10-products) with 1–3 nitrate groups according to their chemical composition. Most of the observed products match expected termination products observed in previous studies, but some compounds such as monomers and dimers with three nitrogen atoms were rarely reported in the literature as gas-phase products from isoprene oxidation by NO3. Possible formation mechanisms for these compounds are proposed. The multi-generation chemistry of isoprene and NO3 is characterized by taking advantages of the time behavior of different products. In addition, the vapor pressures of diverse isoprene nitrates are calculated by different parametrization methods. An estimation of the vapor pressure is also derived from their condensation behavior. According to our results, isoprene monomers belong to intermediate volatility or semi-volatile organic compounds and thus have little effect on SOA formation. In contrast, the dimers are expected to have low or extremely low volatility, indicating that they are potentially substantial contributors to SOA. However, the monomers constitute 80 % of the total explained signals on average, while the dimers contribute less than 2 %, suggesting that the contribution of isoprene NO3 oxidation to SOA by condensation should be low under atmospheric conditions. We expect a SOA mass yield of about 5 % from the wall loss and dilution corrected mass concentrations, assuming that all of the isoprene dimers in the low- or extremely low-volatility organic compound (LVOC or ELVOC) range will condense completely.

Quantitative measurement of remnant thickness in corrosion under pipe supports

There have been many attempts to quantify the wall loss in corrosion under pipe support (CUPS) applications without lifting the pipe to gain access to the corroded area, but none have yielded satisfactory quantitative results. A new method has been developed to enable quantitative estimation of wall loss in CUPS and other applications where direct access to the affected region is not possible. It uses a combination of the non-dispersive SH0 wave and the dispersive SH1 and potentially higher-order modes propagating around the pipe, both in transmission across the defect and reflection from it. The key feature is the rapid reduction in transmission and increase in reflection when the product of the frequency and the remnant wall thickness under the defect approaches the cut-off frequency of the SH1 or higher-order modes. Initial implementation of the method gives quantitative remnant wall thickness results when the wall loss is up to 50%, with qualitative indications of severity at greater defect depths. Blind trial results on a pipe with six defects show a maximum error in the estimated remaining wall thickness of 0.5 mm. The instrument currently covers pipes in the 6-24 inch diameter range and with 6-12 mm wall thickness. This will shortly be expanded and a similar tool to scan circumferentially around the pipe, transmitting and receiving SH waves in the axial direction, is also being developed. This will enable the same defect to be tested from two directions to further increase confidence in the results.

Influence of biomass burning vapor wall loss correction on modeling organic aerosols in Europe by CAMx v6.50

Increasing evidence from experimental studies suggests that the losses of semi-volatile vapors to the chamber walls could be responsible for the underestimation of organic aerosol (OA) in air quality models which use parameters obtained from the chamber experiments. In this study, a box model with volatility basis set (VBS) scheme was developed and the secondary organic aerosol (SOA) yields with vapor wall loss corrected were optimized by a genetic algorithm based on advanced chamber experimental data for biomass burning. The vapor wall loss correction increases the SOA yields by a factor of 1.9–4.9, and leads to a better agreement with the measured OA for 14 chamber experiments under different temperatures and emission loads. To investigate the influence of vapor wall loss correction on regional OA simulations, the optimized parameterizations (SOA yields, emissions of intermediate-volatility organic compounds from biomass burning, and enthalpy of vaporization) were implemented in the regional air quality model CAMx (Comprehensive Air Quality Model with extensions). The modeled results from the standard and vapor wall loss corrected VBS schemes, as well as the traditional two-product approach were compared and evaluated by OA measurements from five Aerodyne aerosol chemical speciation monitor (ACSM)/aerosol mass spectrometer (AMS) stations in the winter of 2011. The vapor wall loss corrected VBS (VBS_WLS) generally shows the best performance for predicting OA among all OA schemes, and reduces the mean fractional bias from −72.9 % (with the standard VBS (VBS_BASE)) to −1.6 % for the winter OA. In Europe, the VBS_WLS produces the highest domain average OA in winter (2.3 µg m−3), which is 106.6 % and 26.2 % higher than the standard VBS and the reference scenario (VBS_noWLS, same parameterization as VBS_WLS, except with the default yields without vapor wall loss correction), respectively. Compared to VBS_noWLS, VBS_WLS leads to an increase in SOA by up to ~ 80 % in Romania. VBS_WLS also leads to a better agreement between the modeled SOA fraction in OA (fSOA) and the estimated measured values in the literature. The substantial influence of vapor wall loss correction on modeled OA in Europe highlights the importance of further improvements in the parameterizations based on laboratory studies with a wider range of chamber conditions and field observations with higher spatial and temporal coverage.

Characterization of an indoor environmental chamber and identification of C1–C4 OVOCs during isoprene ozonolysis

An environmental chamber was built up and characterized at The Hong Kong Polytechnic University. The chamber consists of a 6 m3 poly tetrafluoroethylene-co-perfluoropropyl vinyl ether Teflon film reactor inside a stainless-steel enclosure stocked with a series of online gas-phase and aerosol-phase analytical instruments. Temperature and relative humidity are controllable and can be set to a range of 10–40 ± 1°C and 5–85%, ± 3%, respectively. An air purification system provides zero air for the chamber with concentrations of total volatile organic compounds < 1 ppb, NOX and O3 < 1 ppb and particles concentration < 102 particles·cm−3. Characterization experiments were performed under dry conditions (relative humidity< 5%) and ambient temperature (25°C). Average wall loss rates of O3 and NO2 were observed as 2.92 × 10−6 s−1 and 9.3 × 10−4 s−1 respectively, and the particle wall loss rate was 0.27 h−1. Dark ozonolysis of isoprene was studied using this chamber and the production of C1–C4 oxygenated volatile organic compounds such as formaldehyde, methacrolein and methyl vinyl ketone (MVK) was identified using proton-transfer-reaction time-of-flight mass spectrometry. Results of experiments indicate that this new facility can be used to investigate and simulate the gaseous chemistry and secondary aerosol formation.