Formation of secondary organic aerosols from the ozonolysis of dihydrofurans

In this work we report the study of the ozonolysis of 2,5-dihydrofuran and 2,3-dihydrofuran and the reaction conditions leading to the formation of secondary organic aerosols. The reactions have been carried out in a Teflon chamber filled with synthetic air mixtures at atmospheric pressure and room temperature. The ozonolysis only produced particles in the presence of SO2. Rising relative humidity from 0 to 40% had no effect on the production of secondary organic aerosol in the case of 2,5-dihydrofuran, while it reduced the particle number and particle mass concentrations from the 2,3-dihydrofuran ozonolysis. The water-to-SO2 rate constant ratio for the 2,3-dihydrofuran Criegee intermediate was derived from the secondary organic aerosol (SOA) yields in experiments with different relative humidity values, kH2O/kSO2 = (9.8 ± 3.7) × 10-5. The experimental results show that SO3 may not be the only intermediate involved in the formation or growth of new particles in contrast to the data reported for other Criegee intermediate-SO2 reactions. For the studied reactions, SO2 concentrations remained constant during the experiments, behaving as a catalyst in the production of condensable products. Computational calculations also show that the stabilised Criegee intermediates from the ozonolysis reaction of both 2,5-dihydrofuran and 2,3-dihydrofuran may react with SO2, resulting in the regeneration of SO2 and the formation of low-volatility organic acids.Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicada

Formation of secondary organic aerosols from the ozonolysis of dihydrofurans

In this work we report the study of the ozonolysis of 2,5-dihydrofuran and 2,3-dihydrofuran and the reaction conditions leading to the formation of secondary organic aerosols. The reactions have been carried out in a Teflon chamber filled with synthetic air mixtures at atmospheric pressure and room temperature. The ozonolysis only produced particles in the presence of SO2. Rising relative humidity from 0 to 40% had no effect on the production of secondary organic aerosol in the case of 2,5-dihydrofuran, while it reduced the particle number and particle mass concentrations from the 2,3-dihydrofuran ozonolysis. The water-to-SO2 rate constant ratio for the 2,3-dihydrofuran Criegee intermediate was derived from the secondary organic aerosol (SOA) yields in experiments with different relative humidity values, kH2O/kSO2 = (9.8 ± 3.7) × 10-5. The experimental results show that SO3 may not be the only intermediate involved in the formation or growth of new particles in contrast to the data reported for other Criegee intermediate-SO2 reactions. For the studied reactions, SO2 concentrations remained constant during the experiments, behaving as a catalyst in the production of condensable products. Computational calculations also show that the stabilised Criegee intermediates from the ozonolysis reaction of both 2,5-dihydrofuran and 2,3-dihydrofuran may react with SO2, resulting in the regeneration of SO2 and the formation of low-volatility organic acids.Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicada

Atmospheric sink of styrene, α-methylstyrene, trans-β-methylstyrene and indene: Rate constants and mechanisms of the Cl atoms initiated degradation

The kinetics and products of the oxidation of four aromatic compounds, i.e. styrene, α-methylstyrene, trans-β-methylstyrene and indene, with Cl atoms were determined at atmospheric pressure and room temperature. Kinetic experiments were carried out in a 400 L Teflon reaction chamber using GC-FID for the analysis of reactants and products were determined using a 56 L quartz-glass reactor coupled to FTIR spectrophotometer. The rate constants at 298 K, using different reference compounds, were (in units of cm3 molecule−1 s−1): kstyrene = (1.29 ± 0.52)×10−10, kα-methylstyrene = (1.55 ± 0.27)×10−10, ktrans-β-methylstyrene = (1.09 ± 0.23)×10−10 and kindene = (1.01 ± 0.30)×10−10. Observations with FTIR suggest that the main reaction is the addition of the Cl to the aliphatic chain of the aromatic molecules. We found benzaldehyde, benzoyl chloride, formaldehyde and formyl chloride from styrene; acetophenone, formaldehyde and formyl chloride from α-methylstyrene; and benzaldehyde, formaldehyde and acetyl chloride from trans-β-methylstyrene as the main oxidation products. DFT theoretical calculations were performed in order to shed light on the identification of the reaction products. To the best of our knowledge, this work represents the first determination of the rate coefficients and products for the reaction of the Cl atoms with these compounds, except for the rate constant of styrene which has been studied previously. The loss processes of the title compounds in the atmosphere are mostly controlled by reactions with OH radicals during the day and with NO3 at night, but in coastal areas and some polluted environments, Cl reactions became comparable with OH and NO3 radicals, with lifetimes of 2.2 h for styrene, 1.8 h for AMS, 2.5 h for TBMS and 2.8 h for indene

Secondary organic aerosol formation from styrene photolysis and photooxidation with hydroxyl radicals

The formation of secondary organic aerosol (SOA) generated by irradiating styrene in the presence and/or absence of OH, NOx, H2O vapour and seed aerosol has been investigated for the first time. Experiments were conducted in a smog chamber at 298 K and atmospheric pressure. Styrene decay was measured by gas chromatography with a mass spectrometric detector (GC-MS), and the temporal evolution of the aerosol was monitored using a fast mobility particle sizer (FMPS). The SOA yield increases as the initial styrene concentration increases, leading to yields ranging from 1.8% to 3.5% for styrene photolysis, and from 2.4% to 5.0% for its photooxidation. In both cases, the organic aerosol formation can be expressed by a one-product gas/particle partitioning absorption model. The particle number concentration, mass and yield decrease in the presence of NOx and seed aerosol but increase at higher relative humidity (RH). The gas phase and SOA composition were analysed offline using a filter/denuder sampling system simultaneously collecting gas- and particle-phase products. Benzaldehyde was confirmed as the main gas-phase product of the reaction. However, although products in the particle phase were detected, they could not be identified. Moreover, the aqueous filter extracts were analysed using UV–Visible spectrophotometry to determine differences in the optical properties of SOA produced in the presence and absence of NOx. The results from this work may be used to discuss the implications of atmospheric SOA generation from styrene degradation

Secondary organic aerosol formation from α-methylstyrene atmospheric degradation: Role of NOx level, relative humidity and inorganic seed aerosol

Secondary Organic Aerosol (SOA) formation during the photolysis and OH-photooxidation of α-methylstyrene was investigated using a simulation chamber at atmospheric pressure and room temperature (296 ± 1) K. α-Methylstyrene concentration was followed by gas chromatography with a mass spectrometric detector (GC–MS) and the aerosol production was monitored using a Fast Mobility Particle Sizer (FMPS). The effect of varying α-methylstyrene (0.5 ppm - 2 ppm) and NOx (0.5 ppm - 1.0 ppm) concentrations on SOA formation was explored, as was the effect of the relative humidity (RH) (5–50%) and the presence of inorganic seed particles. Results indicate that SOA yields increase at higher α-methylstyrene concentrations; low NOx and high RH conditions favour more rapid aerosol formation and a higher aerosol yield; SOA formation is independent of seed surface area, within the studied range, for both inorganic seed particles ((NH4)2SO4 and CaCl2). An off-line chemical analysis using a filter/denuder sampling system and GC–MS confirms acetophenone as the main gas phase product in both processes, photolysis and photooxidation. For the first time, SOA composition in α-methylstyrene degradation was analysed, observing acetophenone and acetol as products present in the formed aerosol in presence and absence of NOx

Formation of secondary aerosols from the ozonolysis of styrene: effect of SO2 and H2O.

In this work we report the study of the ozonolysis of styrene and the reaction conditions leading to the formation of secondary aerosols. The reactions have been carried out in a Teflon chamber filled with synthetic air mixtures at atmospheric pressure and room temperature. We have found that the ozonolysis of styrene in the presence of low concentrations of SO2 readily produces new particles under concentrations of reactants lower than those required in experiments in the absence of SO2. Thus, nucleation events occur at concentrations around (5.6 ± 1.7) × 108molecule cm−3 (errors are 2σ±20%) and SO2 is consumed during the experiments. The reaction of the Criegee intermediates with SO2 to produce SO3 and then H2SO4 may explain (together with OH reactions’ contribution) the high capacity of styrene to produce particulate matter in polluted atmospheres. The formation of secondary aerosols in the smog chamber is inhibited under high H2O concentrations. So, the potential formation of secondary aerosols under atmospheric conditions depends on the concentration of SO2 and relative humidity, with a water to SO2 rate constants ratio kH2O/kSO2 = (2.8 ± 0.7) × 10−5 (errors are 2σ±20%)

Impact of SARS-CoV-2 lockdown and de-escalation on air-quality parameters.

The SARS-CoV-2 health crisis has temporarily forced the lockdown of entire countries. This work reportsthe short-term effects on air quality of such unprecedented paralysis of industry and transport indifferent continental cities in Spain, one of the countries most affected by the virus and with the hardestconfinement measures. The study takes into account sites with different sizes and diverse emissionsources, such as traffic, residential or industrial emissions. This work reports newfield measurementdata for the studied pandemic period and assesses the air quality parameters within the historic trend ofeach pollutant and site. Thus, 2013e2020 data series from ground-air quality monitoring networks havebeen analysed tofind out statistically significant changes in atmospheric pollutants during MarcheJune2020 due to this sudden paralysis of activity. The results show substantial concentration drops of primarypollutants, including NOx, CO, BTX, NMHC and NH3. Particulate matter changes were smaller due to theexistence of other natural sources. During the lockdown the ozone patterns were different for eachstudied location, depending on the VOCs-NOx ratios, with concentration changes close to those expectedfrom the historical series in each site and not statistically attributable to the health crisis effects. Finally,the gradual de-escalation and progressive increase of traffic density within cities reflects a slow recoveryof primary pollutants. The results and conclusions for these cities, with different sizes and population,and specific emission sources, may serve as a behavioural model for other continental sites and help understand future crises

Secondary organic aerosol formation from the ozonolysis and oh-photooxidation of 2,5-dimethylfuran

In this study, the O3 and OH radical oxidation of 2,5-dimethylfuran (2,5-DMF) were investigated in two different chambers at (296±1) K and atmospheric pressure to examine secondary organic aerosol (SOA) formation. Results for OH-photooxidation indicate that SOA yieldsdecrease (from 6.2 to 0.4) with the rise of 2,5-DMF concentration (from10 to 1000 ppb). In the absence of NOx and under high relative humidity (RH) conditions (60%), higher aerosol yields are favoured. SOA formation is dependent on the initial seed surface for two kinds of inorganic seed particles ((NH4)2SO4 and CaCl2), being the effect slightly greater for CaCl2. The ozonolysis only generates particles in the presence of SO2 and the increase of relative humidity from 0 to 15% lowers the particle number and particle mass concentrations. The water-to-SO2 rate constant ratio of the Criegee intermediate was derived from the SOA yield in experiments with different relative humidity values, with kH2O/kSO2 = (1.6±0.4)x10−5

Treatment with tocilizumab or corticosteroids for COVID-19 patients with hyperinflammatory state: a multicentre cohort study (SAM-COVID-19)

Objectives: The objective of this study was to estimate the association between tocilizumab or corticosteroids and the risk of intubation or death in patients with coronavirus disease 19 (COVID-19) with a hyperinflammatory state according to clinical and laboratory parameters. Methods: A cohort study was performed in 60 Spanish hospitals including 778 patients with COVID-19 and clinical and laboratory data indicative of a hyperinflammatory state. Treatment was mainly with tocilizumab, an intermediate-high dose of corticosteroids (IHDC), a pulse dose of corticosteroids (PDC), combination therapy, or no treatment. Primary outcome was intubation or death; follow-up was 21 days. Propensity score-adjusted estimations using Cox regression (logistic regression if needed) were calculated. Propensity scores were used as confounders, matching variables and for the inverse probability of treatment weights (IPTWs). Results: In all, 88, 117, 78 and 151 patients treated with tocilizumab, IHDC, PDC, and combination therapy, respectively, were compared with 344 untreated patients. The primary endpoint occurred in 10 (11.4%), 27 (23.1%), 12 (15.4%), 40 (25.6%) and 69 (21.1%), respectively. The IPTW-based hazard ratios (odds ratio for combination therapy) for the primary endpoint were 0.32 (95%CI 0.22-0.47; p < 0.001) for tocilizumab, 0.82 (0.71-1.30; p 0.82) for IHDC, 0.61 (0.43-0.86; p 0.006) for PDC, and 1.17 (0.86-1.58; p 0.30) for combination therapy. Other applications of the propensity score provided similar results, but were not significant for PDC. Tocilizumab was also associated with lower hazard of death alone in IPTW analysis (0.07; 0.02-0.17; p < 0.001). Conclusions: Tocilizumab might be useful in COVID-19 patients with a hyperinflammatory state and should be prioritized for randomized trials in this situatio

Clonal chromosomal mosaicism and loss of chromosome Y in elderly men increase vulnerability for SARS-CoV-2

The pandemic caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2, COVID-19) had an estimated overall case fatality ratio of 1.38% (pre-vaccination), being 53% higher in males and increasing exponentially with age. Among 9578 individuals diagnosed with COVID-19 in the SCOURGE study, we found 133 cases (1.42%) with detectable clonal mosaicism for chromosome alterations (mCA) and 226 males (5.08%) with acquired loss of chromosome Y (LOY). Individuals with clonal mosaic events (mCA and/or LOY) showed a 54% increase in the risk of COVID-19 lethality. LOY is associated with transcriptomic biomarkers of immune dysfunction, pro-coagulation activity and cardiovascular risk. Interferon-induced genes involved in the initial immune response to SARS-CoV-2 are also down-regulated in LOY. Thus, mCA and LOY underlie at least part of the sex-biased severity and mortality of COVID-19 in aging patients. Given its potential therapeutic and prognostic relevance, evaluation of clonal mosaicism should be implemented as biomarker of COVID-19 severity in elderly people. Among 9578 individuals diagnosed with COVID-19 in the SCOURGE study, individuals with clonal mosaic events (clonal mosaicism for chromosome alterations and/or loss of chromosome Y) showed an increased risk of COVID-19 lethality