Acidity, defined as pH, is a central component of aqueous chemistry. In the atmosphere, the acidity of condensed phases (aerosol particles, cloud water, and fog droplets) governs the phase partitioning of semivolatile gases such as HNO₃, NH₃, HCl, and organic acids and bases as well as chemical reaction rates. It has implications for the atmospheric lifetime of pollutants, deposition, and human health. Despite its fundamental role in atmospheric processes, only recently has this field seen a growth in the number of studies on particle acidity. Even with this growth, many fine-particle pH estimates must be based on thermodynamic model calculations since no operational techniques exist for direct measurements. Current information indicates acidic fine particles are ubiquitous, but observationally constrained pH estimates are limited in spatial and temporal coverage. Clouds and fogs are also generally acidic, but to a lesser degree than particles, and have a range of pH that is quite sensitive to anthropogenic emissions of sulfur and nitrogen oxides, as well as ambient ammonia. Historical measurements indicate that cloud and fog droplet pH has changed in recent decades in response to controls on anthropogenic emissions, while the limited trend data for aerosol particles indicate acidity may be relatively constant due to the semivolatile nature of the key acids and bases and buffering in particles. This paper reviews and synthesizes the current state of knowledge on the acidity of atmospheric condensed phases, specifically particles and cloud droplets. It includes recommendations for estimating acidity and pH, standard nomenclature, a synthesis of current pH estimates based on observations, and new model calculations on the local and global scale.

This systematic review aimed to identify the unmet care needs and their associated variables in patients with advanced cancer and informal caregivers, alongside summarizing the tools used for needs assessment. Ten electronic databases were searched systematically from inception of each database to December 2016 to determine eligible studies. Studies that considered the unmet care needs of either adult patients with advanced cancer or informal caregivers, regardless of the study design, were included. The Mixed Methods Appraisal Tool was utilized for quality appraisal of the included studies. Content analysis was used to identify unmet needs, and descriptive analysis was adopted to synthesize other outcomes. Fifty studies were included, and their methodological quality was generally robust. The prevalence of unmet needs varied across studies. Twelve unmet need domains were identified in patients with advanced cancer, and seven among informal caregivers. The three most commonly reported domains for patients were psychological, physical, and healthcare service and information. The most prominent unmet items of these domains were emotional support (10.1–84.4%), fatigue (18–76.3%), and “being informed about benefits and side-effects of treatment” (4–66.7%). The most commonly identified unmet needs for informal caregivers were information needs, including illness and treatment information (26–100%) and care-related information (21–100%). Unmet needs of patients with advanced cancer were associated with their physical symptoms, anxiety, and quality of life. The most commonly used instruments for needs assessment among patients with advanced cancer were the Supportive Care Needs Survey (N = 8) and Problems and Needs in Palliative Care questionnaire (N = 5). The majority of the included studies investigated unmet needs from the perspectives of either patients or caregivers with a cross-sectional study design using single time-point assessments. Moreover, significant heterogeneity, including differences in study contexts, assessment methods, instruments for measurement, need classifications, and reporting methods, were identified across studies. Both advanced cancer patients and informal caregivers reported a wide range of context-bound unmet needs. Examining their unmet needs on the basis of viewing patients and their informal caregivers as a whole unit will be highly optimal. Unmet care needs should be comprehensively evaluated from the perspectives of all stakeholders and interpreted by using rigorously designed mixed methods research and longitudinal studies within a given context.

Strong atmospheric photochemistry in summer can produce a significant amount of secondary aerosols, which may have a large impact on regional air quality and visibility. In the study reported herein, we analyzed sulfate, nitrate, and ammonium in PM_2.5 samples collected using a 24-h filter system at suburban and rural sites near four major cities in China (Beijing, Shanghai, Guangzhou, and Lanzhou). Overall, the PM_2.5 mass concentrations were high (with a mean value of 55–68 gμgm⁻³), which reflects the long-known particulate pollution in China's large urban centers. We observed very high concentrations of sulfate and nitrate at the Beijing and Shanghai sites, and, in particular, abnormally high levels of nitrate (24-h average concentration up to 42 gμgm⁻³ and contributing up to 25% of the PM_2.5 mass) in the ammonium-poor samples. The Beijing and Shanghai aerosols were characterized by high levels of aerosol acidity (~220–390 nmol m⁻³) and low levels of in-situ pH (−0.77 to −0.52). In these samples, the formation of the observed high concentrations of particulate nitrate cannot be explained by homogeneous gas-phase reaction between ammonia and nitric acid. Examination of the relation of nitrate to relative humidity and aerosol loading suggests that the nitrate was most probably formed via the heterogeneous hydrolysis of N₂O₅ on the surface of the moist and acidic aerosols in Beijing and Shanghai. In comparison, the samples collected in Lanzhou and Guangzhou were ammonium-rich with low levels of aerosol acidity (~65–70 nmol m⁻³), and the formation of ammonium nitrate via the homogeneous gas-phase reaction was favored, which is similar to many previous studies. An empirical fit has been derived to relate fine nitrate to aerosol acidity, aerosol water content, aerosol surface area, and the precursor of nitrate for the data from Beijing and Shanghai.