Understanding atmospheric organic aerosols via factor analysis of aerosol mass spectrometry: a review

Organic species are an important but poorly characterized constituent of airborne particulate matter. A quantitative understanding of the organic fraction of particles (organic aerosol, OA) is necessary to reduce some of the largest uncertainties that confound the assessment of the radiative forcing of climate and air quality management policies. In recent years, aerosol mass spectrometry has been increasingly relied upon for highly time-resolved characterization of OA chemistry and for elucidation of aerosol sources and lifecycle processes. Aerodyne aerosol mass spectrometers (AMS) are particularly widely used, because of their ability to quantitatively characterize the size-resolved composition of submicron particles (PM1). AMS report the bulk composition and temporal variations of OA in the form of ensemble mass spectra (MS) acquired over short time intervals. Because each MS represents the linear superposition of the spectra of individual components weighed by their concentrations, multivariate factor analysis of the MS matrix has proved effective at retrieving OA factors that offer a quantitative and simplified description of the thousands of individual organic species. The sum of the factors accounts for nearly 100% of the OA mass and each individual factor typically corresponds to a large group of OA constituents with similar chemical composition and temporal behavior that are characteristic of different sources and/or atmospheric processes. The application of this technique in aerosol mass spectrometry has grown rapidly in the last six years. Here we review multivariate factor analysis techniques applied to AMS and other aerosol mass spectrometers, and summarize key findings from field observations. Results that provide valuable information about aerosol sources and, in particular, secondary OA evolution on regional and global scales are highlighted. Advanced methods, for example a-priori constraints on factor mass spectra and the application of factor analysis to combined aerosol and gas phase data are discussed. Integrated analysis of worldwide OA factors is used to present a holistic regional and global description of OA. Finally, different ways in which OA factors can constrain global and regional models are discussed

Effects of hospital facilities on patient outcomes after cancer surgery: an international, prospective, observational study

Background Early death after cancer surgery is higher in low-income and middle-income countries (LMICs) compared with in high-income countries, yet the impact of facility characteristics on early postoperative outcomes is unknown. The aim of this study was to examine the association between hospital infrastructure, resource availability, and processes on early outcomes after cancer surgery worldwide.Methods A multimethods analysis was performed as part of the GlobalSurg 3 study-a multicentre, international, prospective cohort study of patients who had surgery for breast, colorectal, or gastric cancer. The primary outcomes were 30-day mortality and 30-day major complication rates. Potentially beneficial hospital facilities were identified by variable selection to select those associated with 30-day mortality. Adjusted outcomes were determined using generalised estimating equations to account for patient characteristics and country-income group, with population stratification by hospital.Findings Between April 1, 2018, and April 23, 2019, facility-level data were collected for 9685 patients across 238 hospitals in 66 countries (91 hospitals in 20 high-income countries; 57 hospitals in 19 upper-middle-income countries; and 90 hospitals in 27 low-income to lower-middle-income countries). The availability of five hospital facilities was inversely associated with mortality: ultrasound, CT scanner, critical care unit, opioid analgesia, and oncologist. After adjustment for case-mix and country income group, hospitals with three or fewer of these facilities (62 hospitals, 1294 patients) had higher mortality compared with those with four or five (adjusted odds ratio [OR] 3.85 [95% CI 2.58-5.75]; p<0.0001), with excess mortality predominantly explained by a limited capacity to rescue following the development of major complications (63.0% vs 82.7%; OR 0.35 [0.23-0.53]; p<0.0001). Across LMICs, improvements in hospital facilities would prevent one to three deaths for every 100 patients undergoing surgery for cancer.Interpretation Hospitals with higher levels of infrastructure and resources have better outcomes after cancer surgery, independent of country income. Without urgent strengthening of hospital infrastructure and resources, the reductions in cancer-associated mortality associated with improved access will not be realised

Hygroscopicity of particles at two rural, urban influenced sites during Pacific 2001: Comparison with estimates of water uptake from particle composition

Hygroscopicity of particles was measured at Langley (rural) and Eagle Ridge (semi-rural) as part of the Pacific 2001 field campaign. The measured growth factors at the two sites were comparable. However, differences in particle composition as measured by an Aerosol Mass Spectrometer were evident at these two sites. Sulphate mass concentration was found to be similar at the two sites, while higher nitrate and organic mass were observed at Eagle Ridge. Higher growth factors were observed when the air mass was impacted by SO2 sources, while lower growth factors were observed when the air mass was affected by urban emissions. To examine the hygroscopic role of the different particle components, expected growth factors were calculated from the composition data and compared to measured growth factors. Calculations were done using the Zdanovskii, Stokes and Robinson (ZSR) mixing rule. Sulphate fraction played a dominant role in particle hygroscopicity at both sites. Calculated growth factors were within the uncertainty of the measurements, except when the nitrate fraction was high. The results imply that particulate nitrate takes up much less water than ammonium nitrate, indicating that the ZSR mixing rule fails for nitrate. Small variations of organic growth factors with source regions suggest that secondary organic matter is more hygroscopic than primary organic matter

Refractive index of engine-emitted black carbon and the influence of organic coatings on optical properties

This is the final version. Available on open access from the American Geophysical Union via the DOI in this recordData Availability Statement: The dataset for this research is available at https://doi.org/10.48420/22716904.v1Refractive indices (RI) of particles are important in determining their radiative forcing. We measured optical coefficients of particles classified according to their aerodynamic diameter, allowing retrieval of RI using a Mie model. At 405 nm, the RI of BC from a diesel engine was 1.870 (±0.132) + 0.640 (±0.015) i. The RI of secondary organic aerosol (SOA), using α-pinene and o-cresol as precursors, were 1.584 ± 0.015 and 1.738 (±0.021) + 0.0316 (±0.0018) i, respectively. Neither SOAs demonstrated absorption at 660 nm and their RIs were 1.551 ± 0.011 and 1.586 ± 0.011, the similar value suggesting that a single RI may be sufficient for simulating the radiative forcing of SOA at this wavelength. In addition, organics were condensed onto BC to test optical models for coated particles. For BC particles coated with non-absorbing organics, the extinction is predicted accurately by all models. The absorption is significantly over-estimated by core-shell, volume mixing, and effective medium approximations and under-estimated by external mixing. For BC particles coated with weakly absorbing organics, the extinction and absorption are best described by external mixing when the coating ratio is less than 2.5. When the coating ratio is over 2.5, the difference between the external mixing predictions and measurements increases with the coating ratio. Our results show that the absorption of coated BC particles may not be predicted accurately based solely on the equivalent diameter, coating ratio, and pure component RIs, and considerations of additional factors such as morphology may be necessary.Natural Environment Research Council (NERC)Met OfficeEuropean Union Horizon 202

Mutual promotion effect between aerosol particle liquid water and nitrate formation lead to severe nitrate-dominated particulate matter pollution and low visibility

Abstract. As has been the case in North America and Western Europe, the SO2 emissions substantially reduced in North China Plain (NCP) in recent years. A dichotomy of reductions in SO2 and NOx concentrations result in the frequent occurrences of nitrate (pNO3−)-dominated particulate matter pollution over NCP. In this study, we observed a polluted episode with the nitrate mass fraction in non-refractory PM1 (NR-PM1) up to 44 % during wintertime in Beijing. Based on this typical pNO3−-dominated haze event, the linkage between aerosol water uptake and pNO3− formation, further impacting on visibility degradation, have been investigated based on field observations and theoretical calculations. During haze development, as ambient relative humidity (RH) increased from ~ 10 % up to 70 %, the aerosol particle liquid water increased from ~ 1 μg/m3 at the beginning to ~ 75 μg/m3 at the fully-developed haze period. Without considering the water uptake, the particle surface area and the volume concentrations increased by a factor of 4.1 and 4.8, respectively, during the development of haze event. Taking water uptake into account, the wet particle surface area and volume concentrations enhanced by a factor of 4.7 and 5.8, respectively. As a consequence, the hygroscopic growth of particles facilitated the condensational loss of dinitrogen pentoxide (N2O5) and nitric acid (HNO3) to particles contributing pNO3−. From the beginning to the fully-developed haze, the condensational loss of N2O5 increased by a factor of 20 when only considering aerosol surface area and volume of dry particles, while increasing by a factor of 25 considering extra surface area and volume due to water uptake. Similarly, the condensational loss of HNO3 increased by a factor of 2.7~2.9 and 3.1~3.5 for dry and wet aerosol surface area and volume from the beginning to the fully-developed haze period. Above results demonstrated that the pNO3− formation is further enhanced by aerosol water uptake with elevated ambient RH during haze development, in turn, facilitating the aerosol taking up water due to the hygroscopicity of nitrate salt. Such mutual promotion effect between aerosol particle liquid water and nitrate formation can rapidly degrade air quality and halve visibility within one day. Reduction of nitrogen-containing gaseous precursors, e.g., by control of traffic emissions, is essential in mitigating severe haze events in NCP

Mutual promotion between aerosol particle liquid water and particulate nitrate enhancement leads to severe nitrate-dominated particulate matter pollution and low visibility

As has been the case in North America and western Europe, the SO2 emissions have substantially reduced in the North China Plain (NCP) in recent years. Differential rates of reduction in SO2 and NOx concentrations result in the frequent occurrence of particulate matter pollution dominated by nitrate (pNO3-) over the NCP. In this study, we observed a polluted episode with the particulate nitrate mass fraction in nonrefractory PM1 (NR-PM1) being up to 44 % during wintertime in Beijing. Based on this typical pNO3--dominated haze event, the linkage between aerosol water uptake and pNO3- enhancement, further impacting on visibility degradation, has been investigated based on field observations and theoretical calculations. During haze development, as ambient relative humidity (RH) increased from ĝ1/410 % to 70 %, the aerosol particle liquid water increased from ĝ1/41 μg m-3 at the beginning to ĝ1/475 μg m-3 in the fully developed haze period. The aerosol liquid water further increased the aerosol surface area and volume, enhancing the condensational loss of N2O5 over particles. From the beginning to the fully developed haze, the condensational loss of N2O5 increased by a factor of 20 when only considering aerosol surface area and volume of dry particles, while increasing by a factor of 25 when considering extra surface area and volume due to water uptake. Furthermore, aerosol liquid water favored the thermodynamic equilibrium of HNO3 in the particle phase under the supersaturated HNO3 and NH3 in the atmosphere. All the above results demonstrated that pNO3- is enhanced by aerosol water uptake with elevated ambient RH during haze development, in turn facilitating the aerosol take-up of water due to the hygroscopicity of particulate nitrate salt. Such mutual promotion between aerosol particle liquid water and particulate nitrate enhancement can rapidly degrade air quality and halve visibility within 1 d. Reduction of nitrogen-containing gaseous precursors, e.g., by control of traffic emissions, is essential in mitigating severe haze events in the NCP