The impact of megacity pollution on local climate and implications for the regional environment: Mexico City

We present calculations to estimate potential changes to the local climate and photochemistry caused by pollutants (gases and particles) produced in Mexico City, and the implications for the regional scale when pollutants are exported to surrounding regions. Measured aerosol optical properties are used in a 2-stream delta-Eddington radiative transfer model (Slingo and Schrecker, 1982. Quarterly Journal of the Royal Meteorological Society 108, 407–426) to estimate net radiative fluxes and heating rates, while photolysis rates for nitrogen dioxide and ozone are estimated from a much more detailed model (Madronich, 1987. Journal of Geophysical Research 92, 9740–9752). The presence of highly absorbing aerosols in Mexico City leads to a 17.6% reduction in solar radiative flux at the surface when an optical depth of 0.55 is considered. Photolysis rates for nitrogen dioxide and ozone are reduced between 18 and 21% at the surface, while an increase of between 15 and 17% is predicted above the boundary layer, for local noon calculations.The non-uniform vertical structure of aerosol concentrations observed (Pérez Vidal and Raga, 1998. Atmosfera 11, 95–108) plays a significant role in determining localized regions of heating, i.e. stabilization at the top of the boundary layer that results in a temperature increase of 0.4K h⁻¹ at that level. The presence of a 200 m-deep aerosol layer at the top of the boundary layer results in vertical profiles of the photolysis rates that are significantly different from the case where the aerosols are uniformly distributed in the mixed layer. At the bottom of the aerosol layer (about 1 km above the surface), the rates are about 28% lower than when there is a uniform aerosol distribution in the boundary layer. Finally, there is also an enhancement of photolysis rates at the top of the boundary layer that may lead to increased ozone production compared to the non-aerosol case.     

Investigations of an intense aerosol loading during 2007 cyclone SIDR – A study using satellite data and ground measurements over Indian region

Tropical cyclones are prominent weather systems characterized by high atmospheric pressure gradients and wind speeds. Intense tropical cyclones occur in India during the pre-monsoon (spring), early monsoon (early summer), or post-monsoon (fall) periods. Originating in both the Bay of Bengal (BoB) and the Arabian Sea (AS), these tropical cyclones often attain velocities of more than 100 km h^?1 and are notorious for causing intense rain and storm surge as they cross the Indian coast. In this study, we examine the changes in the aerosol properties associated with an intense tropical cyclone “SIDR”, that occurred during 11–16 November 2007 over BoB. This cyclone, accompanied with very strong surface winds reaching 223 km h^?1, caused extensive damage over Bangladesh. Ground-based measurements of Aerosol Optical Depth (AOD) in the neighboring urban environment of Hyderabad, India, showed significant variations due to changes in wind velocity and direction associated with the cyclone passage. The Terra-MODIS and AVHRR satellite images showed prevalence of dust particles mixed with emissions from anthropogenic sources and biomass-burning AS, while the aerosol loading over BoB was significantly lower. The positive values of Aerosol index (AI) obtained from the Ozone Monitoring Instrument (OMI) suggested the presence of an elevated aerosol layer over the West coast of India, AS and Thar Desert during and after the cyclone episode. Meteorological parameters from the MM5 mesoscale model were used to study the variations in winds associated with the cyclonic activity. Particulate matter loading over the region during the cyclone period increased by ～45% with an accompanying decrease in columnar aerosol optical depth. The variations in Angstrom parameters suggested coarse-mode particle loading due to dust aerosols as observed in satellite data.     

On the contribution of black carbon to the composite aerosol radiative forcing over an urban environment

This paper discusses the extent of Black Carbon (BC) radiative forcing in the total aerosol atmospheric radiative forcing over Pune, an urban site in India. Collocated measurements of aerosol optical properties, chemical composition and BC were carried out for a period of six months (during October 2004 to May 2005) over the site. Observed aerosol chemical composition in terms of water soluble, insoluble and BC components were used in Optical Properties of Aerosols and Clouds (OPAC) to derive aerosol optical properties of composite aerosols. The BC fraction alone was used in OPAC to derive optical properties of BC aerosols. The aerosol optical properties for composite and BC aerosols were separately used in SBDART model to derive direct aerosol radiative forcing due to composite and BC aerosols. The atmospheric radiative forcing for composite aerosols were found to be +35.5, +32.9 and +47.6 Wm^?2 during post-monsoon, winter and pre-monsoon seasons, respectively. The average BC mass fraction found to be 4.83, 6.33 and 4 μg m^?3 during the above seasons contributing around 2.2 to 5.8% to the total aerosol load. The atmospheric radiative forcing estimated due to BC aerosols was +18.8, +23.4 and +17.2 Wm^?2, respectively during the above seasons. The study suggests that even though BC contributes only 2.2–6% to the total aerosol load; it is contributing an average of around 55% to the total lower atmospheric aerosol forcing due to strong radiative absorption, and thus enhancing greenhouse warming.     

Sensitivity of shortwave radiative fluxes to the vertical distribution of aerosol single scattering albedo in the presence of a desert dust layer

The aim of this work is to quantify the sensitivity of shortwave radiative fluxes to changes in the vertical distribution of aerosol absorption, taken into account through the aerosol Single Scattering Albedo (SSA). The case study represents a real atmospheric situation with a desert dust layer (DDL) in the mid troposphere over an urban Boundary Layer (BL) observed at Rome on 20 June 2007. A moderately high aerosol optical depth (AOD), 0.292 at 550 nm, and low Ångström exponent of 0.30 were measured. The observed case was reconstructed with a radiative transfer model, in which the SSA of the boundary layer aerosols was varied from that of a highly absorbing aerosol type (urban) to a highly scattering one (clear marine). The SSA of the DDL is determined keeping fixed the measured SSA of the whole atmospheric column. The simulations show notable changes in the surface and top of the atmosphere (TOA) diffuse fluxes depending on the boundary layer aerosol properties. The aerosol radiative forcing (ARF) at the surface changes by 6–19 W m^?2, depending on the solar zenith angle, when urban or clean marine particles are included in the boundary layer. The ARF differences observed at TOA are between 1 and 5 W m^?2 when urban and clean marine aerosol types in the BL are respectively used, showing a smaller dependency on the solar zenith angle than at the surface.     

Simulation of aerosol direct radiative forcing with RAMS-CMAQ in East Asia

The air quality modeling system RAMS-CMAQ is developed to assess aerosol direct radiative forcing by linking simulated meteorological parameters and aerosol mass concentration with the aerosol optical properties/radiative transfer module in this study. The module is capable of accounting for important factors that affect aerosol optical properties and radiative effect, such as incident wave length, aerosol size distribution, water uptake, and internal mixture. Subsequently, the modeling system is applied to simulate the temporal and spatial variations in mass burden, optical properties, and direct radiative forcing of diverse aerosols, including sulfate, nitrate, ammonium, black carbon, organic carbon, dust, and sea salt over East Asia throughout 2005. Model performance is fully evaluated using various observational data, including satellite monitoring of MODIS and surface measurements of EANET (Acid Deposition Monitoring Network), AERONET (Aerosol Robotic Network), and CSHNET (Chinese Sun Hazemeter Network). The correlation coefficients of the comparisons of daily average mass concentrations of sulfate, PM2.5, and PM10 between simulations and EANET measurements are 0.70, 0.61, and 0.64, respectively. It is also determined that the modeled aerosol optical depth (AOD) is in congruence with the observed results from the AERONET, the CSHNET, and the MODIS. The model results suggest that the high AOD values ranging from 0.8 to 1.2 are mainly distributed over the Sichuan Basin as well as over central and southeastern China, in East Asia. The aerosol direct radiative forcing patterns generally followed the AOD patterns. The strongest forcing effect ranging from −12 to −8 W m⁻² was mainly distributed over the Sichuan Basin and the eastern China’s coastal regions in the all-sky case at TOA, and the forcing effect ranging from −8 to −4 W m⁻² could be found over entire eastern China, Korea, Japan, East China Sea, and the sea areas of Japan     

Aerosol radiative forcing over the Indo-Gangetic plains during major dust storms

Indo-Gangetic (IG) alluvial plains, one of the largest river basins in the world, suffers from the long range transport of mineral dust from the western arid and desert regions of Africa, Arabia and Rajasthan during the summer (pre-monsoon season, April–June). These dust storms influence the aerosol optical depth (AOD) across the IG plains. The Kanpur AERONET (Aerosol Robotic Network) station and Moderate Resolution Imaging Spectro-radiometer (MODIS) data show pronounced effect on the aerosol optical properties and aerosol size distribution during major dust storm events over the IG plains that have significant effect on the aerosol radiative forcing (ARF). The multi-band AOD, from AERONET and MODIS, show contrasting changes in wavelength dependency over dust affected regions. A time collocated (±30 min) validation of AERONET AOD with MODIS Terra (level 2 swath product) over Kanpur, at a common wavelength of 550 nm for the period 2001–2005 show moderate correlation (R²∼0.6) during the summer season. The average surface forcing is found to change by −23 W m⁻² during dust events and the top of the atmosphere (TOA) forcing change by −11 W m⁻² as compared to the non-dusty clear-sky days. A strong correlation is found between AOD at 500 nm and the ARF. At surface, the correlation coefficient between AOD and ARF is found to be high (R²=0.925) and is found to be moderate (R²=0.628) at the TOA. The slope of the regression line gives the aerosol forcing efficiency at 500 nm of about −46±2.6 W m⁻² and −17±2.5 W m⁻² at the surface and the TOA, respectively. The ARF is found to increase with the advance of the dry season in conjunction with the gradual rise in AOD (at 500 nm) from April (0.4–0.5) to June (0.6–0.7) over the IG plains.     

Impact of clouds and aerosols on ozone production in Southeast Texas

A radiative transfer model and photochemical box model are used to examine the effects of clouds and aerosols on actinic flux and photolysis rates, and the impacts of changes in photolysis rates on ozone production and destruction rates in a polluted urban environment like Houston, Texas. During the TexAQS-II Radical and Aerosol Measurement Project the combined cloud and aerosol effects reduced j(NO₂) photolysis frequencies by nominally 17%, while aerosols reduced j(NO₂) by 3% on six clear sky days. Reductions in actinic flux due to attenuation by clouds and aerosols correspond to reduced net ozone formation rates with a nearly one-to-one relationship. The overall reduction in the net ozone production rate due to reductions in photolysis rates by clouds and aerosols was approximately 8 ppbv h^?1.     

Transport of SO2 and aerosol over the Yellow sea

Aircraft measurements of air pollutants were made to investigate the characteristic features of long-range transport of sulfur compounds over the Yellow Sea for the periods of 26–27 April and 7–10 November in 1998, and 9–11 April and 19 June in 1999, together with aerosol measurements at the Taean background station in Korea. The overall mean concentrations of SO₂, O₃ and aerosol number in the boundary layer for the observation period ranged 0.1–7.4 ppb 32.1–64.1 ppb and 1.0–143.6 cm⁻³, respectively. It was found that the air mass over the Yellow Sea had a character of both the polluted continental air and clean background air, and the sulfur transport was mainly confined in the atmospheric boundary layer. The median of SO₂ concentration within the boundary layer was about 0.1–2.2 ppb. However, on 8 November, 1998, the mean concentrations of SO₂ and aerosol number increased up to 7.4 ppb and 109.5 cm⁻³, respectively, in the boundary layer, whereas O₃ concentration decreased remarkably. This enhanced SO₂ concentration occurred in low level westerly air stream from China to Korea. Aerosol analyses at the downstream site of Taean in Korea showed 2–3 times higher sulfate concentration than that of other sampling days, indicating a significant amount of SO₂ conversion to non sea-salt sulfate during the long-range transport.     

Chemical characteristics of atmospheric aerosols over southwest coast of India

Ambient aerosol samples, collected from Mangalore region in the southwest coast of India during the period of late winter (February and March) to early summer (April and May), have been analysed for water-soluble ionic species. Their abundance pattern is dominated by HCO₃⁻, SO₄²⁻, Na⁺, Cl⁻, with minor contribution from NO₃⁻, Ca²⁺, NH₄⁺, K⁺ and Mg²⁺ indicating the contribution from not only sea salt, but also from anthropogenic and dust sources; with pronounced seasonal variability. The suspended particulate matter concentration varied from 35 to 160 μg m⁻³, with consistently higher values during the late winter. Back trajectory analysis suggests the origin of the air masses shifting from Indo-Gangetic Plains (during late winter) to those from the Arabian Sea and the area around Persian Gulf during April–May. Air masses passing over Northern India (Indo-Gangetic Plains) impart characteristic contribution of ionic species from fossil fuel combustion, biomass burning and eolian dust as asserted by the factor analysis. A detailed study on characterisation of aerosols from south Asian region is rather sparse but essential for modelling the effect of tropospheric aerosols on climate.     

An Atmospheric Particulate Sampling Procedure For Gravimetric And Elemental Analyses

Large quantities of atmospheric aerosols with compositions SO₄ ⁼, NO₃ ^? and NH₄ ⁺ have been detected in highly industrialized areas. The major portions of aerosol products are the results of energyrelated fuel combustion. Both microphysical and macrophysical processes are considered in investigating the time dependent evolution of the saturation spectra of condensation nuclei associated with both polluted and clean atmospheres during the time periods of advection fog formation. The results show that the condensation nuclei associated with a polluted atmosphere provide more favorable conditions than condensation nuclei associated with a clean atmosphere to produce dense advection fog, and that attaining a certain degree of supersaturation is not necessarily required for the formation of advection fog with condensation nuclei associated with a polluted atmosphere for monodisperse distribution.     

A contribution of brown carbon aerosol to the aerosol light absorption and its radiative forcing in East Asia

Brown carbon aerosols were recently found to be ubiquitous and effectively absorb solar radiation. We use a 3-D global chemical transport model (GEOS-Chem) together with aircraft and ground based observations from the TRACE-P and the ACE-Asia campaigns to examine the contribution of brown carbon aerosol to the aerosol light absorption and its climatic implication over East Asia in spring 2001. We estimated brown carbon aerosol concentrations in the model using the mass ratio of brown carbon to black carbon (BC) aerosols based on measurements in China and Europe. The comparison of simulated versus observed aerosol light absorption showed that the model accounting for brown carbon aerosol resulted in a better agreement with the observations in East Asian-Pacific outflow. We then used the model results to compute the radiative forcing of brown carbon, which amounts up to ?2.4 W m^?2 and 0.24 W m^?2 at the surface and at the top of the atmosphere (TOA), respectively, over East Asia. Mean radiative forcing of brown carbon aerosol is ?0.43 W m^?2 and 0.05 W m^?2 at the surface and at the TOA, accounting for about 15% of total radiative forcing (?2.2 W m^?2 and 0.33 W m^?2) by absorbing aerosols (BC + brown carbon aerosol), having a significant climatic implication in East Asia.     

The vertical profile of atmospheric heating rate of black carbon aerosols at Kanpur in northern India

Altitude profiles of the mass concentrations of aerosol black carbon (BC) and composite aerosols were obtained from the collocated measurements of these quantities onboard an aircraft, over the urban area of Kanpur, in the Ganga basin of northern India during summer, for the first time in India. The enhancement in the mean BC concentration was observed at ∼1200 m in the summer, but the vertical gradient of BC concentration is less than the standard deviation at that altitude. The difference in the BC altitude profile and columnar concentration in the winter and summer is attributed to the enhanced turbulent mixing within the boundary layer in summer. This effect is more conspicuous with BC than the composite aerosols, resulting in an increase in the BC mass fraction (F_BC) at higher levels in summer. This high BC fraction results in an increase in the lower atmospheric heating rate in both the forenoon, FN and afternoon, AN, but with contrasting altitude profile. The FN profile shows fluctuating trend with highest value (2.1 K day⁻¹) at 300 m and a secondary peak at 1200 m altitudes, whereas the AN profile shows increasing trend with highest value (1.82 K day⁻¹) at 1200 m altitude.     

Spatial distribution of aerosol black carbon over India during pre-monsoon season

Aerosol black carbon (BC) mass concentrations ([BC]), measured continuously during a mutli-platform field experiment, Integrated Campaign for Aerosols gases and Radiation Budget (ICARB, March–May 2006), from a network of eight observatories spread over geographically distinct environments of India, (which included five mainland stations, one highland station, and two island stations (one each in Arabian Sea and Bay of Bengal)) are examined for their spatio-temporal characteristics. During the period of study, [BC] showed large variations across the country, with values ranging from 27 μg m^?3 over industrial/urban locations to as low as 0.065 μg m^?3 over the Arabian Sea. For all mainland stations, [BC] remained high compared to highland as well as island stations. Among the island stations, Port Blair (PBR) had higher concentration of BC, compared to Minicoy (MCY), implying more absorbing nature of Bay of Bengal aerosols than Arabian Sea. The highland station Nainital (NTL), in the central Himalayas, showed low values of [BC], comparable or even lower than that of the island station PBR, indicating the prevalence of cleaner environment over there. An examination of the changes in the mean temporal features, as the season advances from winter (December–February) to pre-monsoon (March–May), revealed that: (a) Diurnal variations were pronounced over all the mainland stations, with an afternoon low and a nighttime high; (b) At the islands, the diurnal variations, though resembled those over the mainlands, were less pronounced; and (c) In contrast to this, highland station showed an opposite pattern with an afternoon high and a late night or early morning low. The diurnal variations at all stations are mainly caused by the dynamics of local Atmospheric Boundary Layer (ABL). At the entire mainland as well as island stations (except HYD and DEL), [BC] showed a decreasing trend from January to May. This is attributed to the increased convective mixing and to the resulting enhanced vertical dispersal of species in the ABL. In addition, large short-period modulations were observed at DEL and HYD, which appeared to be episodic. An examination of this in the light of the MODIS-derived fire count data over India along with the back-trajectory analysis revealed that advection of BC from extensive forest fires and biomass-burning regions upwind were largely responsible for this episodic enhancement in BC at HYD and DEL.     

Simulation of aerosol radiative properties with the ORISAM-RAD model during a pollution event (ESCOMPTE 2001)

The aim of this study is to present the organic and inorganic spectral aerosol module-radiative (ORISAM-RAD) module, allowing the 3D distribution of aerosol radiative properties (aerosol optical depth, single scattering albedo and asymmetry parameter) from the ORISAM module. In this work, we test ORISAM-RAD for one selected day (24th June) during the ESCOMPTE (expérience sur site pour contraindre les modèles de pollution atmosphérique et de transport d’emissions) experiment for an urban/industrial aerosol type. The particle radiative properties obtained from in situ and AERONET observations are used to validate our simulations. In a first time, simulations obtained from ORISAM-RAD indicate high aerosol optical depth (AOD)0.50–0.70±0.02 (at 440 nm) in the aerosol pollution plume, slightly lower (10–20%) than AERONET retrievals. In a second time, simulations of the single scattering albedo (ω_o) have been found to well reproduce the high spatial heterogeneities observed over this domain. Concerning the asymmetry parameter (g), ORISAM-RAD simulations reveal quite uniform values over the whole ESCOMPTE domain, comprised between 0.61±0.01 and 0.65±0.01 (at 440 nm), in excellent agreement with ground based in situ measurements and AERONET retrievals. Finally, the outputs of ORISAM-RAD have been used in a radiative transfer model in order to simulate the diurnal direct radiative forcing at different locations (urban, industrial and rural). We show that anthropogenic aerosols strongly decrease surface solar radiation, with diurnal mean surface forcings comprised between −29.0±2.9 and −38.6±3.9 W m⁻², depending on the sites. This decrease is due to the reflection of solar radiations back to space (−7.3±0.8<ΔF_TOA<−12.3±1.2 W m⁻²) and to its absorption into the aerosol layer (21.1±2.1<ΔF_ATM<26.3±2.6 W m⁻²). These values are found to be consistent with those measured at local scale.     

Aerosol radiative forcing for Asian continental outflow

Asian aerosols in elevated layers over the Pacific Ocean were sampled with NASA wire-impactors and a FSSP optical particle spectrometer-probe aboard the NASA DC-8 aircraft in early March 1994. Strong variations in aerosol properties, primarily aerosol concentration, lead to derived mid-visible extinctions between 0.003 and 0.5/km. FSSP data usually identified two size-modes. The larger ‘coarse mode’ (radii of 1–3 μm) was assumed to be dust. The composition of the smaller ‘accumulation mode’ (radii of 0.1–0.3 μm) was based on the analysis of the wire-impactor samples, as significant amounts of soot reduce mid-visible single scattering albedos to the 0.87–0.92 range.Radiative forcing simulations investigated the impact of Asian outflow aerosol on atmospheric radiative fluxes and heating rates. Only events with larger optical depths were important. In those events the solar attenuation of the smaller size mode dominated the net-flux losses at the surface, with values similar those of urban-polluted and/or biomass burning aerosol types (as observed during the TARFOX and INDOEX field experiments). In contrast, changes to net-fluxes at the top of the atmosphere (ToA) for outflow cases are less negative—primarily due to the added greenhouse effect of the dust component. For the climate of the Earth-Atmosphere-System, ToA net-flux losses are considered a cooling, ToA net-flux gains are associated with warming. Weak cooling is determined for the Asian outflow cases under cloud-free conditions. The addition of a reported 50% cloud cover below the aerosol layer causes a switch to slight warming.     

Spectroscopic study of organic coatings on fine particles,exposed to ozone and simulated sunlight

This work intends to quantify the variation in optical properties of aerosol by in-situ spectroscopic monitoring the ozonolysis of a mixture of typical biomass burning compounds. The reaction occurs on silica and glass particles in the presence of simulated sunlight.Fused silica particles (Aerosil) were coated with a thin film of a 1:1 mixure of 4-phenoxyphenol with 4-carboxyphenone as a photosensitizer. UV–VIS spectra of dichloromethane extracts from the particles recorded before and after treatment, show development of a new band after prolonged ozone and light exposure.Changes in optical properties are reported, and variations of spectroscopic features are discussed. We show that the ozone-induced heterogeneous photochemical reaction does produce species absorbing light in the solar spectral range. Further, we demonstrate that the heterogeneous photosensitized reactions at 200 ppb ozone (strongly ozone polluted regions) for a time period of 7 h aging process, can increase light absorption of atmospheric aerosols in the tropospheric actinic window (>290 nm) by 0.4 absorption units ng-C^?1 O₃ ppm^?1 in the region 290–358 nm and by 1.0 absorption units ng-C^?1 O₃ ppm^?1 in the region 360–448 nm.Chemical changes of such surface films were identified by diffuse reflectance infrared Fourier transform spectroscopy of coated glass spheres, and we suggest formation of humic-like substances comparable to those reported in continental aerosol.     

Estimating bulk optical properties of aerosols over the western North Pacific by using MODIS and CERES measurements

Over the western North Pacific, a large amount of land aerosols from Asian-Pacific countries is transported by the prevailing westerlies. This transport makes the radiative characteristics of these aerosols diverse, particularly when one compares those characteristics over the coastal sea with those over the open sea. In this paper we discuss a method that uses satellite data to obtain the single-scattering albedo (ω) and asymmetry factor (g) of atmospheric aerosols for two large-scale subdivisions—the coastal sea (within 250 km from the coast) and the open sea (the remaining area)—over the western North Pacific (110°E–180°, 20°N–50°N). Our estimation method uses satellite measurements, obtained over a six-year period (2000–2005), of aerosol optical depth (AOD) and shortwave fluxes at both the surface and the top of the atmosphere (TOA); the measurements are obtained using the Moderate Resolution Imaging Spectroradiometer (MODIS) and the Clouds and the Earth's Radiant Energy System (CERES). For the two subdivisions, the estimated annual means of (ω,g) at 630 nm are significantly different: (0.94, 0.65) over the coastal sea and (0.97, 0.70) over the open sea. From a quantitative viewpoint, this result indicates that in comparison with aerosols over the open sea, those over the coastal sea show greater absorption and lesser forward scattering of solar radiation. The estimated optical properties are responsible for the aerosol surface cooling observed by MODIS and CERES, which is approximately 138 and 108 W m⁻² per AOD over the coastal sea and open sea, respectively.     

Present and potential future contributions of sulfate,black and organic carbon aerosols from China to global air quality,premature mortality and radiative forcing

Aerosols are harmful to human health and have both direct and indirect effects on climate. China is a major contributor to global emissions of sulfur dioxide (SO₂), a sulfate (SO₄^2?) precursor, organic carbon (OC), and black carbon (BC) aerosols. Although increasingly examined, the effect of present and potential future levels of these emissions on global premature mortality and climate change has not been well quantified. Through both direct radiative effects and indirect effects on clouds, SO₄^2? and OC exert negative radiative forcing (cooling) while BC exerts positive forcing (warming). We analyze the effect of China's emissions of SO₂, SO₄^2?, OC and BC in 2000 and for three emission scenarios in 2030 on global surface aerosol concentrations, premature mortality, and radiative forcing (RF). Using global models of chemical transport (MOZART-2) and radiative transfer (GFDL RTM), and combining simulation results with gridded population data, mortality rates, and concentration–response relationships from the epidemiological literature, we estimate the contribution of Chinese aerosols to global annual premature mortality and to RF in 2000 and 2030. In 2000, we estimate these aerosols cause approximately 470 000 premature deaths in China and an additional 30 000 deaths globally. In 2030, aggressive emission controls lead to a 50% reduction in premature deaths from the 2000 level to 240 000 in China and 10 000 elsewhere, while under a high emissions scenario premature deaths increase 50% from the 2000 level to 720 000 in China and to 40 000 elsewhere. Because the negative RF from SO₄^2? and OC is larger than the positive forcing from BC, Chinese aerosols lead to global net direct RF of ?74 mW m^?2 in 2000 and between ?15 and ?97 mW m^?2 in 2030 depending on the emissions scenario. Our analysis indicates that increased effort to reduce greenhouse gases is essential to address climate change as China's anticipated reduction of aerosols will result in the loss of net negative radiative forcing.     

Inferring episodic atmospheric iron fluxes in the Western South Atlantic

Iron (Fe) and other trace elements such as Zn, Mn, Ni and Cu are known as key-factors in marine biogeochemical cycles. It is believed that ocean primary productivity blooms in iron deficient regions can be triggered by iron in aeolian dust. Up to now, scarce aerosol elemental composition, based on measurements over sea at the Western South Atlantic (WSA), exist. An association between the Patagonian semi-desert dust/Fe and chlorophyll-a variability at the Argentinean continental shelf is essentially inferred from models. We present here experimental data of Fe enriched aerosols over the WSA between latitudes 22°S–62°S, during 4 oceanographic campaigns between 2002 and 2005. These data allowed inferring the atmospheric Fe flux onto different latitudinal bands which varied from 30.4 to 1688 nmolFe m^?2 day^?1 (October 29th–November 15th, 2003); 5.83–1586 nmolFe m^?2 day^?1 (February 15th–March 6th, 2004) and 4.73–586 nmolFe m^?2 day^?1(October 21st–November 5th, 2005).