A dual-chamber method for quantifying the effects of atmospheric perturbations on secondary organic aerosol formation from biomass burning emissions

Biomass burning (BB) is a major source of atmospheric pollutants. Field and laboratory studies indicate that secondary organic aerosol (SOA) formation from BB emissions is highly variable. We investigated sources of this variability using a novel dual-smog-chamber method that directly compares the SOA formation from the same BB emissions under two different atmospheric conditions. During each experiment, we filled two identical Teflon smog chambers simultaneously with BB emissions from the same fire. We then perturbed the smoke with UV lights, UV lights plus nitrous acid (HONO), or dark ozone in one or both chambers. These perturbations caused SOA formation in nearly every experiment with an average organic aerosol (OA) mass enhancement ratio of 1.78 ± 0.91 (mean ± 1σ). However, the effects of the perturbations were highly variable ranging with OA mass enhancement ratios ranging from 0.7 (30% loss of OA mass) to 4.4 across the set of perturbation experiments. There was no apparent relationship between OA enhancement and perturbation type, fuel type, and modified combustion efficiency. To better isolate the effects of different perturbations, we report dual-chamber enhancement (DUCE), which is the quantity of the effects of a perturbation relative to a reference condition. DUCE values were also highly variable, even for the same perturbation and fuel type. Gas measurements indicate substantial burn-to-burn variability in the magnitude and composition of SOA precursor emissions, even in repeated burns of the same fuel under nominally identical conditions. Therefore, the effects of different atmospheric perturbations on SOA formation from BB emissions appear to be less important than burn-to-burn variability

Rule-based embedded HMMs phoneme classification to improve Qur’anic recitation recognition

Phoneme classification performance is a critical factor for the successful implementation of a speech recognition system. A mispronunciation of Arabic short vowels or long vowels can change the meaning of a complete sentence. However, correctly distinguishing phonemes with vowels in Quranic recitation (the Holy book of Muslims) is still a challenging problem even for state-of-the-art classification methods, where the duration of the phonemes is considered one of the important features in Quranic recitation, which is called Medd, which means that the phoneme lengthening is governed by strict rules. These features of recitation call for an additional classification of phonemes in Qur’anic recitation due to that the phonemes classification based on Arabic language characteristics is insufficient to recognize Tajweed rules, including the rules of Medd. This paper introduces a Rule-Based Phoneme Duration Algorithm to improve phoneme classification in Qur’anic recitation. The phonemes of the Qur’anic dataset contain 21 Ayats collected from 30 reciters and are carefully analyzed from a baseline HMM-based speech recognition model. Using the Hidden Markov Model with tied-state triphones, a set of phoneme classification models optimized based on duration is constructed and integrated into a Quranic phoneme classification method. The proposed algorithm achieved outstanding accuracy, ranging from 99.87% to 100% according to the Medd type. The obtained results of the proposed algorithm will contribute significantly to Qur’anic recitation recognition models

Impact of opioid-free analgesia on pain severity and patient satisfaction after discharge from surgery: multispecialty, prospective cohort study in 25 countries

Background: Balancing opioid stewardship and the need for adequate analgesia following discharge after surgery is challenging. This study aimed to compare the outcomes for patients discharged with opioid versus opioid-free analgesia after common surgical procedures.Methods: This international, multicentre, prospective cohort study collected data from patients undergoing common acute and elective general surgical, urological, gynaecological, and orthopaedic procedures. The primary outcomes were patient-reported time in severe pain measured on a numerical analogue scale from 0 to 100% and patient-reported satisfaction with pain relief during the first week following discharge. Data were collected by in-hospital chart review and patient telephone interview 1 week after discharge.Results: The study recruited 4273 patients from 144 centres in 25 countries; 1311 patients (30.7%) were prescribed opioid analgesia at discharge. Patients reported being in severe pain for 10 (i.q.r. 1-30)% of the first week after discharge and rated satisfaction with analgesia as 90 (i.q.r. 80-100) of 100. After adjustment for confounders, opioid analgesia on discharge was independently associated with increased pain severity (risk ratio 1.52, 95% c.i. 1.31 to 1.76; P < 0.001) and re-presentation to healthcare providers owing to side-effects of medication (OR 2.38, 95% c.i. 1.36 to 4.17; P = 0.004), but not with satisfaction with analgesia (beta coefficient 0.92, 95% c.i. -1.52 to 3.36; P = 0.468) compared with opioid-free analgesia. Although opioid prescribing varied greatly between high-income and low- and middle-income countries, patient-reported outcomes did not.Conclusion: Opioid analgesia prescription on surgical discharge is associated with a higher risk of re-presentation owing to side-effects of medication and increased patient-reported pain, but not with changes in patient-reported satisfaction. Opioid-free discharge analgesia should be adopted routinely

The Brown–Black Continuum of Light-Absorbing Combustion Aerosols

Brown carbon (BrC) exhibits highly variable light-absorption properties, with the imaginary part of the refractive indices (<i>k</i>) varying over several orders of magnitude. This poorly understood variability poses a challenge to accurately determining the BrC climate effect. Here, we present a framework to explain the variability in BrC <i>k</i>. We hypothesize that a fraction of BrC is composed of black-carbon (BC) precursors whose transformation to BC is not complete, and that there is a continuum of light-absorption properties along which BC and BrC lie. To test this hypothesis, we performed controlled-combustion experiments using benzene and toluene. By systematically varying the combustion conditions, we isolated BrC components along the brown–black continuum progressing from light (<i>k</i> = 0.004 at 550 nm) to dark (<i>k</i> = 0.25 at 550 nm). Using laser-desorption-ionization mass spectrometry and thermodenuder measurements, we show that the BrC progression from light to dark is associated with an increase in molecular size and decrease in volatility. The darkest BrC has molecular sizes of several 1000 Da, is refractory, and is optically more similar to BC than the lighter BrC, blurring the lines between the optical properties of BrC and BC

Probing the Evaporation Dynamics of Mixed SOA/Squalane Particles Using Size-Resolved Composition and Single-Particle Measurements

An analysis of the formation and evaporation of mixed-particles containing squalane (a surrogate for hydrophobic primary organic aerosol, POA) and secondary organic aerosol (SOA) is presented. In these experiments, one material (D₆₂-squalane or SOA from α-pinene + O₃) was prepared first to serve as surface area for condensation of the other, forming the mixed-particles. The mixed-particles were then subjected to a heating-ramp from 22 to 44 °C. We were able to determine that (1) almost all of the SOA mass is comprised of material less volatile than D₆₂-squalane; (2) AMS collection efficiency in these mixed-particle systems can be parametrized as a function of the relative mass fraction of the components; and (3) the vast majority of D₆₂-squalane is able to evaporate from the mixed particles, and does so on the same time scale regardless of the order of preparation. We also performed two-population mixing experiments to directly test whether D₆₂-squalane and SOA from α-pinene + O₃ form a single solution or two separate phases. We find that these two OA types are immiscible, which informs our inference of the morphology of the mixed-particles. If the morphology is core–shell and dictated by the order of preparation, these data indicate that squalane is able to diffuse relatively quickly through the SOA shell, implying that there are no major diffusion limitations

Probing the Evaporation Dynamics of Mixed SOA/Squalane Particles Using Size-Resolved Composition and Single-Particle Measurements

An analysis of the formation and evaporation of mixed-particles containing squalane (a surrogate for hydrophobic primary organic aerosol, POA) and secondary organic aerosol (SOA) is presented. In these experiments, one material (D₆₂-squalane or SOA from α-pinene + O₃) was prepared first to serve as surface area for condensation of the other, forming the mixed-particles. The mixed-particles were then subjected to a heating-ramp from 22 to 44 °C. We were able to determine that (1) almost all of the SOA mass is comprised of material less volatile than D₆₂-squalane; (2) AMS collection efficiency in these mixed-particle systems can be parametrized as a function of the relative mass fraction of the components; and (3) the vast majority of D₆₂-squalane is able to evaporate from the mixed particles, and does so on the same time scale regardless of the order of preparation. We also performed two-population mixing experiments to directly test whether D₆₂-squalane and SOA from α-pinene + O₃ form a single solution or two separate phases. We find that these two OA types are immiscible, which informs our inference of the morphology of the mixed-particles. If the morphology is core–shell and dictated by the order of preparation, these data indicate that squalane is able to diffuse relatively quickly through the SOA shell, implying that there are no major diffusion limitations

Organic Aerosol Mixing Observed by Single-Particle Mass Spectrometry

We present direct measurements of mixing between separately prepared organic aerosol populations in a smog chamber using single-particle mass spectra from the high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS). Docosane and docosane-<i>d</i>₄₆ (22 carbon linear solid alkane) did not show any signs of mixing, but squalane and squalane-<i>d</i>₆₂ (30 carbon branched liquid alkane) mixed on the time scale expected from a condensational-mixing model. Docosane and docosane-<i>d</i>₄₆ were driven to mix when the chamber temperature was elevated above the melting point for docosane. Docosane vapors were shown to mix into squalane-<i>d</i>₆₂, but not the other way around. These results are consistent with low diffusivity in the solid phase of docosane particles. We performed mixing experiments on secondary organic aerosol (SOA) surrogate systems finding that SOA derived from toluene-<i>d</i>₈ (a surrogate for anthropogenic SOA (aSOA)) does not mix into squalane (a surrogate for hydrophobic primary organic aerosol (POA)) but does mix into SOA derived from α-pinene (biogenic SOA (bSOA) surrogate). For the aSOA/POA, the volatility of either aerosol does not limit gas-phase diffusion, indicating that the two particle populations do not mix simply because they are immiscible. In the aSOA/bSOA system, the presence of toluene-<i>d</i>₈-derived SOA molecules in the α-pinene-derived SOA provides evidence that the diffusion coefficient in α-pinene-derived SOA is high enough for mixing on the time scale of 1 min. The observations from all of these mixing experiments are generally invisible to bulk aerosol composition measurements but are made possible with single-particle composition data

Secondary Organic Aerosol Production from Gasoline Vehicle Exhaust: Effects of Engine Technology, Cold Start, and Emission Certification Standard

Secondary organic aerosol (SOA) formation from dilute exhaust from 16 gasoline vehicles was investigated using a potential aerosol mass (PAM) oxidation flow reactor during chassis dynamometer testing using the cold-start unified cycle (UC). Ten vehicles were equipped with gasoline direct injection engines (GDI vehicles) and six with port fuel injection engines (PFI vehicles) certified to a wide range of emissions standards. We measured similar SOA production from GDI and PFI vehicles certified to the same emissions standard; less SOA production from vehicles certified to stricter emissions standards; and, after accounting for differences in gas-particle partitioning, similar effective SOA yields across different engine technologies and certification standards. Therefore the ongoing, dramatic shift from PFI to GDI vehicles in the United States should not alter the contribution of gasoline vehicles to ambient SOA and the natural replacement of older vehicles with newer ones certified to stricter emissions standards should reduce atmospheric SOA levels. Compared to hot operations, cold-start exhaust had lower effective SOA yields, but still contributed more SOA overall because of substantially higher organic gas emissions. We demonstrate that the PAM reactor can be used as a screening tool for vehicle SOA production by carefully accounting for the effects of the large variations in emission rates