Andrea Pozzer

The contribution of outdoor air pollution sources to premature mortality on a global scale

Assessment of the global burden of disease is based on epidemiological cohort studies that connect premature mortality to a wide range of causes, including the long-term health impacts of ozone and fine particulate matter with a diameter smaller than 2.5 micrometres (PM2.5). It has proved difficult to quantify premature mortality related to air pollution, notably in regions where air quality is not monitored, and also because the toxicity of particles from various sources may vary. Here we use a global atmospheric chemistry model to investigate the link between premature mortality and seven emission source categories in urban and rural environments. In accord with the global burden of disease for 2010 (ref. 5), we calculate that outdoor air pollution, mostly by PM2.5, leads to 3.3 (95 per cent confidence interval 1.61–4.81) million premature deaths per year worldwide, predominantly in Asia. We primarily assume that all particles are equally toxic, but also include a sensitivity study that accounts for differential toxicity. We find that emissions from residential energy use such as heating and cooking, prevalent in India and China, have the largest impact on premature mortality globally, being even more dominant if carbonaceous particles are assumed to be most toxic. Whereas in much of the USA and in a few other countries emissions from traffic and power generation are important, in eastern USA, Europe, Russia and East Asia agricultural emissions make the largest relative contribution to PM2.5, with the estimate of overall health impact depending on assumptions regarding particle toxicity. Model projections based on a business-as-usual emission scenario indicate that the contribution of outdoor air pollution to premature mortality could double by 2050.

Atmosphere-ocean ozone exchange: A global modeling study of biogeochemical, atmospheric, and waterside turbulence dependencies

Received 9 July 2008; revised 12 June 2009; accepted 17 July 2009; published 7 November 2009. [1] The significance of the removal of tropospheric ozone by the oceans, covering 2/3 of the Earth’s surface, has only been addressed in a few studies involving water tank, aircraft, and tower flux measurements. On the basis of results from these few observations of the ozone dry deposition velocity (VdO3), atmospheric chemistry models generally apply an empirical, constant ocean uptake rate of 0.05 cm s 1 . This value is substantially smaller than the atmospheric turbulent transport velocity for ozone. On the other hand, the uptake is higher than expected from the solubility of ozone in clean water alone, suggesting that there is an enhancement in oceanic ozone uptake, e.g., through a chemical destruction mechanism. We present an evaluation of a global-scale analysis with a new mechanistic representation of atmosphere-ocean ozone exchange. The applied atmosphere chemistry-climate model includes not only atmospheric but also waterside turbulence and the role of waterside chemical loss processes as a function of oceanic biogeochemistry. The simulations suggest a larger role of biogeochemistry in tropical and subtropical ozone oceanic uptake with a relative small temporal variability, whereas in midlatitude and high-latitude regions, highly variable ozone uptake rates are expected because of the stronger influence of waterside turbulence. Despite a relatively large range in the explicitly calculated ocean uptake rate, there is a surprisingly small sensitivity of simulated Marine Boundary Layer ozone concentrations compared to the sensitivity for the commonly applied constant ocean uptake approach. This small sensitivity points at compensating effects through inclusion of the process-based ocean uptake mechanisms to consider variability in oceanic O3 deposition consistent with that in atmospheric and oceanic physical, chemical, and biological processes.

Model projected heat extremes and air pollution in the eastern Mediterranean and Middle East in the twenty-first century

The eastern Mediterranean and Middle East, a region with diverse socioeconomic and cultural identities, is exposed to strong climatic gradients between its temperate north and arid south. Model projections of the twenty-first century indicate increasing hot weather extremes and decreasing rainfall. We present model results, which suggest that across the Balkan Peninsula and Turkey climate change is particularly rapid, and especially summer temperatures are expected to increase strongly. Temperature rise can be amplified by the depletion of soil moisture, which limits evaporative cooling, prompted by the waning of large-scale weather systems that generate rain. Very hot summers that occurred only rarely in the recent past are projected to become common by the middle and the end of the century. Throughout the region, the annual number of heat wave days may increase drastically. Furthermore, conditions in the region are conducive for photochemical air pollution. Our model projections suggest strongly increasing ozone formation, a confounding health risk factor particularly in urban areas. This adds to the high concentrations of aerosol particles from natural (desert dust) and anthropogenic sources. The heat extremes may have strong impacts, especially in the Middle East where environmental stresses are plentiful.

Assessing the effect of marine isoprene and ship emissions on ozone, using modelling and measurements from the South Atlantic Ocean

Environmental context. Air over the remote Southern Atlantic Ocean is amongst the cleanest anywhere on the planet. Yet in summer a large-scale natural phytoplankton bloom emits numerous natural reactive compounds into the overlying air. The productive waters also support a large squid fishing fleet, which emits significant amounts of NO and NO2. The combination of these natural and man-made emissions can efficiently produce ozone, an important atmospheric oxidant. Abstract. Ship-borne measurements have been made in air over the remote South Atlantic and Southern Oceans in January–March 2007. This cruise encountered a large-scale natural phytoplankton bloom emitting reactive hydrocarbons (e.g. isoprene); and a high seas squid fishing fleet emitting NOx (NO and NO2). Using an atmospheric chemistry box model constrained by in-situ measurements, it is shown that enhanced ozone production ensues from such juxtaposed marine biogenic and anthropogenic emissions. The relative impact of shipping and phytoplankton emissions on ozone was examined on a global scale using the EMAC model. Ozone in the marine boundary layer was found to be over ten times more sensitive to NOx emissions from ships, than to marine isoprene in the region south of 45°. Although marine isoprene emissions make little impact on the global ozone budget, co-located ship and phytoplankton emissions may explain the increasing ozone reported for the 40–60°S southern Atlantic region.

Aerosol Health Effects from Molecular to Global Scales

Poor air quality is globally the largest environmental health risk. Epidemiological studies have uncovered clear relationships of gaseous pollutants and particulate matter (PM) with adverse health outcomes, including mortality by cardiovascular and respiratory diseases. Studies of health impacts by aerosols are highly multidisciplinary with a broad range of scales in space and time. We assess recent advances and future challenges regarding aerosol effects on health from molecular to global scales through epidemiological studies, field measurements, health-related properties of PM, and multiphase interactions of oxidants and PM upon respiratory deposition. Global modeling combined with epidemiological exposure-response functions indicates that ambient air pollution causes more than four million premature deaths per year. Epidemiological studies usually refer to PM mass concentrations, but some health effects may relate to specific constituents such as bioaerosols, polycyclic aromatic compounds, and transition metals. Various analytical techniques and cellular and molecular assays are applied to assess the redox activity of PM and the formation of reactive oxygen species. Multiphase chemical interactions of lung antioxidants with atmospheric pollutants are crucial to the mechanistic and molecular understanding of oxidative stress upon respiratory deposition. The role of distinct PM components in health impacts and mortality needs to be clarified by integrated research on various spatiotemporal scales for better evaluation and mitigation of aerosol effects on public health in the Anthropocene.

Impact of agricultural emission reductions on fine particulate matter and public health

A global chemistry-climate model has been used to study the impacts of pollutants released by agriculture on fine-particulate matter (PM2.5), with a focus on Europe, North America, East and South Asia. Simulations reveal that a relatively strong reduction in PM2.5 levels can be achieved by decreasing agricultural emissions, notably of ammonia (NH3) released from fertilizer use and animal husbandry. The absolute impact on PM2.5 reduction is strongest in East Asia, even for small emission decreases. Conversely, over Europe and North America, aerosol formation is not immediately limited by the availability of ammonia. Nevertheless, reduction of NH3 can also substantially decrease PM2.5 concentrations over the latter regions, especially when emissions are abated systematically. Our results document how reduction of agricultural emissions decreases aerosol pH due to the depletion of aerosol ammonium, which affects particle liquid phase and heterogeneous chemistry. Further, it is shown that a 50 % reduction of agricultural emissions could prevent the mortality attributable to air pollution by ∼ 250000 people yr−1 worldwide, amounting to reductions of 30, 19, 8 and 3 % over North America, Europe, East and South Asia, respectively. A theoretical 100 % reduction could even reduce the number of deaths globally by about 800 000 per year.

Strong sesquiterpene emissions from Amazonian soils

The Amazon rainforest is the world’s largest source of reactive volatile isoprenoids to the atmosphere. It is generally assumed that these emissions are products of photosynthetically driven secondary metabolism and released from the rainforest canopy from where they influence the oxidative capacity of the atmosphere. However, recent measurements indicate that further sources of volatiles are present. Here we show that soil microorganisms are a strong, unaccounted source of highly reactive and previously unreported sesquiterpenes (C15H24; SQT). The emission rate and chemical speciation of soil SQTs were determined as a function of soil moisture, oxygen, and rRNA transcript abundance in the laboratory. Based on these results, a model was developed to predict soil–atmosphere SQT fluxes. It was found SQT emissions from a Terra Firme soil in the dry season were in comparable magnitude to current global model canopy emissions, establishing an important ecological connection between soil microbes and atmospherically relevant SQTs.Recent measurements in the Amazon rainforest indicate missing sources of volatile organic compounds (VOCs). Here the authors show that soil microorganisms are a strong, unaccounted source of highly reactive sesquiterpenes, a class of VOCs that can regulate ozone chemistry within the forest canopy.

Oxidation processes in the Eastern Mediterranean atmosphere: Evidence from the Modelling of HOx Measurements over Cyprus

The Mediterranean is a climatically sensitive region located at the crossroads of air masses from three continents: Europe, Africa, and Asia. The chemical processing of air masses over this region has implications not only for the air quality but also for the long-range transport of air pollution. To obtain a comprehensive understanding of oxidation processes over the Mediterranean, atmospheric concentrations of the hydroxyl radical (OH) and the hydroperoxyl radical (HO2) were measured during an intensive field campaign (CYprus PHotochemistry EXperiment, CYPHEX2014) in the northwest of Cyprus in the summer of 2014. Very low local anthropogenic and biogenic emissions around the measurement location provided a vantage point to study the contrasts in atmospheric oxidation pathways under highly processed marine air masses and those influenced by relatively fresh emissions from mainland Europe. The CYPHEX measurements were used to evaluate OH and HO2 simulations using a photochemical box model (CAABA/MECCA) constrained with CYPHEX observations of O3, CO, NOx , hydrocarbons, peroxides, and other major HOx (OH+HO2) sources and sinks in a low-NOx environment (< 100 pptv of NO). The model simulations for OH agreed to within 10 % with in situ OH observations. Model simulations for HO2 agreed to within 17 % of the in situ observations. However, the model strongly under-predicted HO2 at high terpene concentrations, this under-prediction reaching up to 38 % at the highest terpene levels. Different schemes to improve the agreement between observed and modelled HO2, including changing the rate coefficients for the reactions of terpene-generated peroxy radicals (RO2) with NO and HO2 as well as the autoxidation of terpenegenerated RO2 species, are explored in this work. The main source of OH in Cyprus was its primary production from O3 photolysis during the day and HONO photolysis during early morning. Recycling contributed about one-third of the total OH production, and the maximum recycling efficiency was about 0.7. CO, which was the largest OH sink, was also the largest HO2 source. The lowest HOx production and losses occurred when the air masses had higher residence time over the oceans.

The Impact of Fine Particulate Outdoor Air Pollution to Premature Mortality

Epidemiological cohort studies have shown that the long-term exposure to PM2.5 is associated with increased mortality from cardiorespiratory diseases and lung cancer. We use an atmospheric chemistry-general circulation model in combination with population data, country-level health statistics and pollution exposure response functions to investigate the link between premature mortality and several emission source categories, combining all aerosol types that contribute to PM2.5. We estimate the global premature mortality by PM2.5 at 3.15 million/year in 2010. We find that high emissions levels mainly from residential energy use have the largest impact on premature mortality in Eastern and Southeastern Asia (almost 70 % of the global), with China and India being the counties with higher mortality levels attributable. For Europe we estimate 375 thousand premature deaths (about 11 % of the global rate), and 274 thousand deaths for the Eastern Mediterranean region in 2010. In this work we assume that all particles are equally toxic.

The South Asian monsoon—Pollution pump and purifier

South Asian monsoon and pollution Air pollution is growing fastest in monsoon-impacted South Asia. During the dry winter monsoon, the fumes disperse toward the Indian Ocean, creating a vast pollution haze. The fate of these fumes during the wet summer monsoon has been unclear. Lelieveld et al. performed atmospheric chemistry measurements by aircraft in the Oxidation Mechanism Observations campaign, sampling the summer monsoon outflow in the upper troposphere between the Mediterranean and the Indian Ocean. The measurements, supported by model calculations, show that the monsoon sustains a remarkably efficient cleansing mechanism in which contaminants are rapidly oxidized and deposited on Earths surface. However, some pollutants are lofted above the monsoon clouds and chemically processed in a reactive reservoir before being redistributed globally, including to the stratosphere. Science, this issue p. 270 The South Asian monsoon removes some air pollution and disperses the rest. Air pollution is growing fastest in monsoon-affected South Asia. During the dry winter monsoon, the fumes disperse toward the Indian Ocean, creating a vast pollution haze, but their fate during the wet summer monsoon has been unclear. We performed atmospheric chemistry measurements by aircraft in the Oxidation Mechanism Observations campaign, sampling the summer monsoon outflow in the upper troposphere between the Mediterranean and the Indian Ocean. The measurements, supported by model calculations, show that the monsoon sustains a remarkably efficient cleansing mechanism by which contaminants are rapidly oxidized and deposited to Earth’s surface. However, some pollutants are lofted above the monsoon clouds and chemically processed in a reactive reservoir before being redistributed globally, including to the stratosphere.