Sulfur Chemistry at the Air-Water Interface.

The global distributions of sulfate and soot particles in the atmosphere are calculated, and the effect of aerosol particles on tropospheric oxidants is studied using a global chemical/transport/aerosol model. The model is developed in the framework of the National Center for Atmospheric Research (NCAR) global three‐dimensional chemical/transport model (Model for Ozone and Related Chemical Tracers (MOZART)). In addition to the gas‐phase photochemistry implemented in the MOZART model, the present study also accounts for the formation of sulfate and black carbon aerosols as well as for heterogeneous reactions on particles. The simulated global sulfate aerosol distributions and seasonal variation are compared with observations. The seasonal variation of sulfate aerosols is in agreement with measurements, except in the Arctic region. The calculated vertical profiles of sulfate aerosol agree well with the observations over North America. In the case of black carbon the calculated surface distribution is in fair agreement with observations. The effects of aerosol formation and heterogeneous reactions on the surface of sulfate aerosols are studied. The model calculations show the following: (1) The concentration of H2O2 is reduced when sulfate aerosols are formed due to the reaction of SO2 + H2O2 in cloud droplets. The gas‐phase reaction SO2 + OH converts OH to HO2, but the reduction of OH and enhancement of HO2 are insignificant (<3%). (2) The heterogeneous reaction of HO2 on the surface of sulfate aerosols produces up to 10% reduction of hydroperoxyl radical (HO2) with an uptake coefficient of 0.2. However, this uptake coefficient could be overestimated, and the results should be regard as an upper limit estimation. (3) The N2O5 reaction on the surface of sulfate aerosols leads to an 80% reduction of NOx at middle to high latitudes during winter. Because ozone production efficiency is low in winter, ozone decreases by only 10% as a result of this reaction. However, during summer the N2O5 reaction reduces NOx by 15% and O3 by 8–10% at middle to high latitudes. (4) The heterogeneous reaction of CH2O on sulfate aerosols with an upper limit uptake coefficient (γ = 0.01) leads to an 80 to 90% decrease in CH2O and 8 to 10% reduction of HO2 at middle to high latitudes during winter. Many uncertainties remain in our understanding of heterogeneous chemical processes and in the estimate of kinetic parameters. This model study should therefore be regarded as exploratory and subject to further improvements before final conclusions can be made.

IIt has been assumed that damage from exposure to tobacco smoke and other particulate air pollutants is imposed primarily on the lungs and is associated with increased morbidity and mortality rates in patients with preexisting lung disease. This is supported by a considerable amount of previous data, such as the mortality data from the December 1952 London smog disaster, which may have caused as many as 12 000 deaths, almost all in patients with preexisting lung disease.1 Total suspended particulate matter (PM) was as high as 3000 μg/m3. Similar patterns of elevated morbidity and mortality rates, primarily in patients with preexisting lung disease, have been documented in other acute episodes of air pollution in the past.2 However, evidence from the past 10 years shows that sudden increases in ambient air pollution can also rapidly raise morbidity and mortality rates in patients with existing cardiovascular disease, as much or more than the rise associated with lung disease. In the present issue of Circulation , Pope and associates3 report interesting new data on the effects on mortality rate of long-term differences, as opposed to sudden transient increases, in levels of air pollution. Data were derived from a large, comprehensive study initiated by the American Cancer Society and linked to cancer prevention. The study involved a large population of subjects enrolled in 1982 from metropolitan centers in all 50 states and Puerto Rico. Vital status of participants was collected every 2 years for the subsequent 16 years, and a cause of death was identified for 98% of the known fatalities. Metropolitan area of residence was known for each participant, and particle counts of fine particulates were averaged over quarterly intervals throughout the year for each included metropolitan area. A questionnaire provided additional data, allowing for differences in mortality …

Background.In recent years, poor urban air quality in Delhi, India has gained significant attention. Episodic events including crop stubble burning and Diwali celebrations are considered major factors in the worsening quality of ambient air.Objective.This study aimed to investigate spatial and monthly variation as well as the role of episodic events in ambient air quality in Delhi, including the ‘Great Smog' month of November 2017.Methods.Monitoring of air pollutants (particulate matter (PM10, PM2.5, PM1) and nitrogen dioxide (NO2)) was carried out at three distinct locations of Delhi from April 2017–February 2018. The concentration of NO2 was measured using a modified Jacob and Hochheiser method and PM was measured using a GRIMM aerosol spectrometer. Air quality index was also determined to identify the effects of air pollution on human health.Results.Overall, the levels of air pollution were found to be approximately 2.1–3.2 times higher along a traffic intersection and about 1.4–2.0 times higher in a commercial area compared with an institutional area. The highest average monthly concentrations of PM10, PM2.5, PM1 and NO2 were 768, 374, 298 and 149 μg/m3, respectively, during the Great Smog month of November 2017. November and August were recorded as the most polluted and cleanest months, respectively, in the city. Generally, poor to severe categories of the air quality index (AQI) were obtained from October to February. Higher concentrations during November were attributed to stubble burning in the nearby states of Delhi with the additive effect of fireworks during Diwali celebrations.Conclusions.Severe ambient air quality as observed in the present study is a serious matter of concern for the health of Delhi's population. To control spikes in poor air quality during episodic events, it is imperative to raise awareness among farmers regarding the severe health hazards of stubble burning.Competing Interests.The authors declare no competing financial interests.

Sulfate aerosol is one of the major components of secondary fine particulate matter in urban haze that has crucial impacts on the social economy and public health. Among the atmospheric sulfate sources, Mn(II)-catalyzed SO2 oxidation on aerosol surfaces has been regarded as a dominating one. In this work, we measured the reaction kinetics of Mn(II)-catalyzed SO2 oxidation in single droplets using an aerosol optical tweezer. We show that the SO2 oxidation occurs at the Mn(II)-active sites on the aerosol surface, per a piecewise kinetic formulation, one that is characterized by a threshold surface Mn(II) concentration and gaseous SO2 concentration. When the surface Mn(II) concentration is lower than the threshold value, the reaction rate is first order with respect to both Mn(II) and SO2, agreeing with our traditional knowledge. But when surface Mn(II) concentration is above the threshold, the reaction rate becomes independent of Mn(II) concentration, and the reaction order with respect to SO2 becomes greater than unity. The measured reaction rate can serve as a tool to estimate sulfate formation based on field observation, and our established parametrization corrects these calculations. This framework for reaction kinetics and parametrization holds promising potential for generalization to various heterogeneous reaction pathways.

Modeling heterogeneous chemical processes on aerosol surface

The air-water interface is the largest interface in the environment. Atmospheric droplets, such as fog, which can have an exceptionally high surface area-to-volume ratio, also have a large range of physical and chemical properties (e.g. temperature, pH, ionic strength, and chemical composition) based on location, time of day, and emission source. Unlike larger atmospheric droplets, which are predominately characterized by bulk aqueous phase conditions, reactions that take place in fog droplets are determined by both the bulk-aqueous phase and the air-water interface due to a high surface area-to-volume ratio. In order to have a greater understanding of atmospheric processes and the fate of environmental pollutants (e.g. benzene and other carbonyl compounds) in fog droplets, both laboratory and field studies are necessary. The reaction of benzene, a common primary atmospheric pollutant, with the hydroxyl radical, was studied in both a bulk-phase reactor and a thin film flow-tube reactor as a laboratory study. For both reactor systems, temperature, pH, ionic strength, and the concentration of oxygen were varied to simulate fog event conditions. Using the thin-film reactor, in particular, has the advantage in that the effect of both bulk and surface conditions on this model reaction can be obtained by adjusting the liquid volume over a given surface area inside the reactor. Volatile organic compounds (VOCs), like benzene, can also degrade in the environment by oxidation to form carbonyl compounds, which, like benzene, are also ubiquitous air, cloud, and fog water pollutants. Furthermore, they also form secondary organic aerosol (SOA) and are precursors to photochemical smog. In order to better understand fog/smog processes and characterization, fog water samples, collected in Baton Rouge, LA, were analyzed for aldehydes and ketones with a method adapted from U.S. EPA Method 8315A. By using a manual injection online concentration system, all liquid-liquid extraction and concentration steps from the original method were eliminated and the required sample volume was reduced. Doing so also shortened the procedure time and lowered the limit of detection.

Megacities are metropolitan areas with populations over 10 million, and many of them are facing significant global environmental challenges such as air pollution. Intense economic and human activities in megacities result in air pollution emissions, inducing high levels of air pollutants in the atmosphere that harm human health, cause regional haze and acid deposition, damage crops, influence regional air quality, and contribute to climate change. Since the Great London Smog and the first recognized episode of Los Angeles photochemical smog seventy years ago, substantial progress has been achieved in improving the scientific understanding of air pollution and in developing emissions reduction technologies and control measures. However, much remains to be understood about the complex processes of atmospheric transport and reaction mechanisms; the formation and evolution of secondary particles, especially those containing organic species; and the influence of emerging emissions sources and changing climate on air quality and health. Molina (DOI: ) has provided an excellent overview of the sources of emissions in megacities, atmospheric physicochemical processes, air quality trends and management, and the impacts on health and climate for the introductory lecture of this Faraday Discussion.

Little is known about the long-term effects of air pollution exposure and the root causes of asthma. We use exposure to intense air pollution from the 1952 Great Smog of London as a natural experiment to examine both issues. To determine whether exposure to extreme air pollution in utero or soon after birth affects asthma development later in life. This was a natural experiment using the unanticipated pollution event by comparing the prevalence of asthma between those exposed to the Great Smog in utero or the first year of life with those conceived well before or after the incident and those residing outside the affected area at the time of the smog. Prevalence of asthma during childhood (ages 0-15) and adulthood (ages >15) is analyzed for 2,916 respondents to the Life History portion of the English Longitudinal Study on Aging born from 1945 to 1955. Exposure to the Great Smog in the first year of life increases the likelihood of childhood asthma by 19.87 percentage points (95% confidence interval [CI], 3.37-36.38). We also find suggestive evidence that early-life exposure led to a 9.53 percentage point increase (95% CI, -4.85 to 23.91) in the likelihood of adult asthma and exposure in utero led to a 7.91 percentage point increase (95% CI, -2.39 to 18.20) in the likelihood of childhood asthma. These results are the first to link early-life pollution exposure to later development of asthma using a natural experiment, suggesting the legacy of the Great Smog is ongoing.

Martin Lengwiler In the following chapter, I will analyse the changing styles of accident prevention in Switzerland from the end of the nineteenth century to the 1960s. Embedding the Swiss case into a comparative perspective including Germany, Britain and the USA, I will argue that the methodological innovations introduced into accident prevention before and during the Second World War had an important methodological influence on the styles of postwar health education undertaken by institutions of public health. Particularly, the strategies of visualisation in postwar health education have profited a lot, at least in the case of Switzerland, from the distinct professional experiences that institutions of occupational safety had acquired before 1945. Although we only know very little about the early history of the use of modem media in public health, it seems that, in European countries, institutions of public health have used the audio and visual opportunities of modem media since their early days in the 1930s.1 The national socialist regime in Germany was presumably the first to lead innovative, media-based campaigns in public health, notably with their anti-tobacco campaign for the prevention of cancer.2 However, the Nazis' innovations in public health did not survive the collapse of the regime in 1945, and most European countries developed their media-based approaches in public health in the 1950s and 1960s without referring to German policies. In Britain, the use of modem media was partly motivated by domestic purposes, as with the vaccination programmes of the 1950s, the need to promote the newly implemented National Health Service through television, or, after the 'great London smog' of 1952, by the question of industrial air pollution.3 Other countries like Switzerland or Germany, as I will point out below, also learned from public health in the USA and its methodological experiences during and immediately after the Second World War.

Air pollution has been recognized as a threat to human health since the time of Hippocrates, ca 400 BC. Successive written accounts of air pollution occur in different countries through the following two millennia until measurements, from the eighteenth century onwards, show the growing scale of poor air quality in urban centres and close to industry, and the chemical characteristics of the gases and particulate matter. The industrial revolution accelerated both the magnitude of emissions of the primary pollutants and the geographical spread of contributing countries as highly polluted cities became the defining issue, culminating with the great smog of London in 1952. Europe and North America dominated emissions and suffered the majority of adverse effects until the latter decades of the twentieth century, by which time the transboundary issues of acid rain, forest decline and ground-level ozone became the main environmental and political air quality issues. As controls on emissions of sulfur and nitrogen oxides (SO2 and NOx) began to take effect in Europe and North America, emissions in East and South Asia grew strongly and dominated global emissions by the early years of the twenty-first century. The effects of air quality on human health had also returned to the top of the priorities by 2000 as new epidemiological evidence emerged. By this time, extensive networks of surface measurements and satellite remote sensing provided global measurements of both primary and secondary pollutants. Global emissions of SO2 and NOx peaked, respectively, in ca 1990 and 2018 and have since declined to 2020 as a result of widespread emission controls. By contrast, with a lack of actions to abate ammonia, global emissions have continued to grow.This article is part of a discussion meeting issue ‘Air quality, past present and future’.

Discussing the impact of air pollution on heart disease

Air pollution and mortality in Europe

The indirect effect of anthropogenic aerosols, whereby aerosol particles change cloud optical properties, is the most uncertain component of climate forcing over the past 100 years. Here we use a mechanistic treatment of droplet nucleation and a prognostic treatment of the number of cloud droplets to study the indirect aerosol effect from changes in carbonaceous and sulfate aerosols. Cloud droplet nucleation is parameterized as a function of total aerosol number concentration, updraft velocity, and an activation parameter, which takes into account the mechanism of sulfate aerosol formation. Where previous studies focussed either on sulfate aerosols or carbonaceous aerosols only, here we estimate the combined effect. The combined indirect aerosol effect amounts to −1.1 W m−2 for an internally mixed aerosol and −1.5 W m−2 for an externally mixed aerosol compared to −1.4 W m−2, which we obtained by empirically relating sulfate mass to cloud droplet number. In the case of an internally mixed aerosol, the contribution from increasing carbonaceous and sulfate aerosols is close to being additive as the individual simulations yield an indirect effect of −0.4 W m−2 due to anthropogenic sulfate aerosols and −0.9 W m−2 due to anthropogenic carbonaceous aerosols. The contribution of anthropogenic sulfate to the indirect effect is close to zero if an externally mixed aerosol is assumed, while the contribution of carbonaceous aerosols increases to −1.3 W m−2. The effect of sulfate in the external mixture approach is much smaller than that of carbonaceous aerosols because its burden only increases by a third of that of carbonaceous aerosols and because the mode radius of sulfate is much larger than that of black and organic carbon.

Concerns about air pollution have a long and complex history. Complaints about its effects on human health and the urban environment were first voiced by the inhabitants of ancient Athens and Rome. But urban air quality worsened considerably during the Industrial Revolution, as the widespread use of coal in factories in Britain, Germany, the United States and other nations ushered in an ‘age of smoke’. Despite the tangible nature of this form of air pollution, early laws to control it were generally weak and ineffective—regardless of its high socio-environmental costs—reflecting the importance of coal-fuelled steam power to economic growth. Not until the mid-twentieth century, after major air pollution episodes such as London’s ‘Great Smog’ had demonstrated beyond doubt that polluted air was as harmful to the public’s health as polluted water supplies, were stringent national laws to abate smoke finally introduced to clear the skies over the cities of the first industrial nations. However, while the citizens of the developed world now breathe cleaner air, smoke pollution is still a significant environmental problem in many industrial cities of developing countries today. In terms of their scale, the effects of coal smoke in the nineteenth and early twentieth centuries were largely local and regional. But after the Second World War a number of invisible threats began to emerge—acid rain, photochemical smog, ozone depletion and climate change—that were transnational and global in character. It often required the cooperation of scientific experts across academic and political borders, as well as new techniques such as computer modelling, to make these new threats ‘visible’ to the public. Global environmental problems also required collective political and legislative action on the part of nations if solutions were to be found. The success of the Montreal Protocol in phasing out the use of ozone-depleting CFCs stands as a successful example of international environmental governance. However, it will need a strong commitment to international cooperation if an effective agreement to reduce greenhouse gas emissions is to be reached, particularly as global warming is a concept that the public (and many politicians) still find difficult to grasp.

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