Search

Remote sensing observations suggest Greenland ice sheet (GrIS) albedo has declined since 2001, even in the dry snow zone. We seek to explain the apparent dry snow albedo decline. We analyze samples representing 2012–2014 snowfall across NW Greenland for black carbon and dust light-absorbing impurities (LAI) and model their impacts on snow albedo. Albedo reductions due to LAI are small, averaging 0.003, with episodic enhancements resulting in reductions of 0.01–0.02. No significant increase in black carbon or dust concentrations relative to recent decades is found. Enhanced deposition of LAI is not, therefore, causing significant dry snow albedo reduction or driving melt events. Analysis of Collection 5 Moderate Resolution Imaging Spectroradiometer (MODIS) surface reflectance data indicates that the decline and spectral shift in dry snow albedo contains important contributions from uncorrected Terra sensor degradation. Though discrepancies are mostly below the stated accuracy of MODIS products, they will require revisiting some prior conclusions with C6 data.

Quantification of the black carbon (BC) and brown carbon (BrC) components of source emissions is critical to understanding the impact combustion aerosols have on atmospheric light absorption. Multiple-wavelength absorption was measured from fuels including wood, agricultural biomass, coals, plant matter, and petroleum distillates in controlled combustion settings. Filter-based absorption measurements were corrected and compared to photoacoustic absorption results. BC absorption was segregated from the total light extinction to estimate the BrC absorption from individual sources. Results were compared to elemental carbon (EC)/organic carbon (OC) concentrations to determine composition's impact on light absorption. Multiple-wavelength absorption coefficients, Angstrom exponent (6.9 to 0.9 OC/TC), source emissions have variable absorption spectra, and nonbiomass combustion sources can be significant contributors to BrC.

[1] This study presents >5 cumulative years of tropospheric mercury (Hg) speciation measurements, over the period of 2003-2009, for eight sites in the central and eastern United States and one site in coastal Puerto Rico. The purpose of this research was to identify local and regional processes that impact Hg speciation and deposition (wet + dry) across a large swath of North America. Sites sampled were selected to represent both a wide range of mercury exposure and environmental conditions. Seasonal mean concentrations of elemental Hg (1.27 ± 0.31 to 2.94 ± 1.57 ng m -3 ; x ± σ), reactive gaseous mercury (RGM; 1.5 ± 1.6 to 63.3 ± 529 pg m -3 ), and fine particulate Hg (1.2 ± 1.4 to 37.9 ± 492 pg m -3 ) were greatest at sites impacted by Hg point sources. Diel bin plots of Hg° and RGM suggest control by a variety of local/regional processes including impacts from Hg point sources and boundary layer/free tropospheric interactions as well as from larger-scale processes affecting Hg speciation (i.e., input of the global Hg pool, RGM formed from oxidation of Hg° by photochemical compounds at coastal sites, and elemental Hg depletion during periods of dew formation). Comparison of wet Hg deposition (measured), RGM and fine particulate Hg dry deposition (calculated using a multiple resistance model), and anthropogenic point source emissions varied significantly between sites. Significant correlation between emission sources and dry deposition was observed but was highly dependant upon inclusion of data from two sites with exceptionally high deposition. Findings from this study highlight the importance of environmental setting on atmospheric Hg cycling and deposition rates.

[1] We present the first near-real time (12 min) measurements of fine particle (PM2.5) water soluble ferrous iron (WS_Fe(II)) measured in two urban settings: Dearborn Michigan, and Atlanta, Georgia. A new approach was used to measure WS_Fe(II) involving a Particle-into-Liquid Sampler (PILS) coupled to a liquid waveguide capillary cell (LWCC) and UV/VIS spectrometer. We found no clear diurnal trends in WS_Fe(II) at any urban site studied. High temporal variability, however, was observed at all urban sites, where concentrations often changed from the method limit of detection (4.6 ng m−3) to approximately 300 to 400 ng m−3, lasting only a few hours. These transient events predominately occurred during times of low wind speeds and appeared to be from local sources or processes. In Atlanta, several WS_Fe(II) events were associated with sulfate plumes, and highest WS_Fe(II) concentrations were found in plumes of highest apparent aerosol acidity. At all locations studied, WS_Fe(II) was poorly correlated (R2 < 0.34) with light-absorbing aerosol, indicating no direct linkage between mobile source emissions and enhanced WS_Fe(II) concentrations. WS_Fe(II) measured within a prescribed forest-burn was strongly correlated with water soluble potassium (R2 = 0.88; WS_Fe(II)/WS_K = 15 mg/g), pointing to biomass burning as a source of WS_Fe(II); however, peak concentrations within the fire were low compared to transient events observed at the urban sites. Overall, WS_Fe(II) temporal trends for these urban sites consisted of low background concentrations with periodic short duration transient events that appear to be linked to unique industrial emissions or atmospheric processing of industrial emissions that form WS_Fe(II).

[1] This study focuses on improving source apportionment of carbonaceous aerosol in South Asia and consists of three parts: (1) development of novel molecular marker–based profiles for real-world biofuel combustion, (2) application of these profiles to a year-long data set, and (3) evaluation of profiles by an in-depth sensitivity analysis. Emissions profiles for biomass fuels were developed through source testing of a residential stove commonly used in South Asia. Wood fuels were combusted at high and low rates, which corresponded to source profiles high in organic carbon (OC) or high in elemental carbon (EC), respectively. Crop wastes common to the region, including rice straw, mustard stalk, jute stalk, soybean stalk, and animal residue burnings, were also characterized. Biofuel profiles were used in a source apportionment study of OC and EC in Godavari, Nepal. This site is located in the foothills of the Himalayas and was selected for its well-mixed and regionally impacted air masses. At Godavari, daily samples of fine particulate matter (PM2.5) were collected throughout the year of 2006, and the annual trends in particulate mass, OC, and EC followed the occurrence of a regional haze in South Asia. Maximum concentrations occurred during the dry winter season and minimum concentrations occurred during the summer monsoon season. Specific organic compounds unique to aerosol sources, molecular markers, were measured in monthly composite samples. These markers implicated motor vehicles, coal combustion, biomass burning, cow dung burning, vegetative detritus, and secondary organic aerosol as sources of carbonaceous aerosol. A molecular marker–based chemical mass balance (CMB) model provided a quantitative assessment of primary source contributions to carbonaceous aerosol. The new profiles were compared to widely used biomass burning profiles from the literature in a sensitivity analysis. This analysis indicated a high degree of stability in estimates of source contributions to OC when different biomass profiles were used. The majority of OC was unapportioned to primary sources and was estimated to be of secondary origin, while biomass combustion was the next-largest source of OC. The CMB apportionment of EC to primary sources was unstable due to the diversity of biomass burning conditions in the region. The model results suggested that biomass burning and fossil fuel were important contributors to EC, but could not reconcile their relative contributions.

[1] Concentrations of atmospheric mercury observed during July and August of 2005 in Riverside, CA and during August of 2006 at sites throughout the Los Angeles Basin indicate that a diurnal pattern of elemental mercury frequently exists within the basin during summer months. During these diurnal cycles, elemental mercury is observed to abruptly spike well above global background levels during the morning hours. These peak events were observed to be coincident across several monitoring sites throughout the Basin suggesting that mercury spikes were not a result of source plumes unique to each site but rather the impact of a basin-wide phenomenon. Atmospheric temperature profiles measured by a Radio Acoustic Sounding System (RASS) located in Moreno Valley, CA indicate that peak events coincided with the shift in surface temperature profile from stable to neutral indicating the presence of fumigation episodes, the occurrence of which is supported by a generic model of basin dispersion. The presence of mercury in the stable layer aloft is a function of point sources within the basin, and in particular a single, elevated point source located in the Port of Long Beach. The unique dynamics of atmospheric mercury observed throughout the Los Angeles Basin combined with the location of this major point source upwind of the Basin provide a novel method of directly observing atmospheric mixing associated with the break-up of the nocturnal inversion layer.

[1] Iron is hypothesized to be an important micronutrient for ocean biota, thus modulating carbon dioxide uptake by the ocean biological pump. Studies have assumed that atmospheric deposition of iron to the open ocean is predominantly from mineral aerosols. For the first time we model the source, transport, and deposition of iron from combustion sources. Iron is produced in small quantities during fossil fuel burning, incinerator use, and biomass burning. The sources of combustion iron are concentrated in the industrialized regions and biomass burning regions, largely in the tropics. Model results suggest that combustion iron can represent up to 50% of the total iron deposited, but over open ocean regions it is usually less than 5% of the total iron, with the highest values (

[1] The sulfur transport and deposition model (STEM) is used to study the aerosol seasonality, distribution, and composition over south Asia from September 2004 to August 2005. Model predictions of sulfate, black carbon, primary organic carbon, other anthropogenic particulate matter, windblown mineral dusts, and sea salt are compared at two sites in south Asia where yearlong experimental observations are available from the Atmospheric Brown Cloud (ABC) project. The model predictions are able to capture both the magnitude and seasonality of aerosols over Hanimaadhoo Observatory, Maldives. However, the model is not able to explain the seasonality at the Kathmandu Observatory; but the model does capture Kathmandu's observed annual mean concentration. The absence of seasonal brick kiln emissions within Kathmandu valley in the current inventory is a probable reason for this problem. This model study reveals high-anthropogenic aerosol loading over the Ganges valley even in the monsoonal months, which needs to be corroborated by experimental observations. Modeling results also show a high dust loading over south Asia with a distinct seasonality. Model results of aerosol monthly composition are also presented at five cities in south Asia. Total and fine-mode monthly aerosol optical depth along with contribution from each aerosol species is presented; the results show that the anthropogenic fraction dominates in the postmonsoon and the early dry season with major contributions from sulfate and absorbing aerosols. Model sensitivity studies of dry deposition velocity and wet scavenging efficiency show that model improvements are needed in the treatment of carbonaceous aerosol dry and wet removal processes. Modeled SO2 conversion rate constrained with sulfate observations at Hanimaadhoo suggests the need to increase model sulfate production rate during the dry season to account for probable sulfate production via heterogeneous pathways.

[1] Atmospheric particulate matter samples were collected at two Maldives climate observatories from 30 August 2004 to 21 January 2005. This time period encompassed both wet and dry seasons, which correspond to low and high aerosol loadings. High aerosol loadings were observed in the northern sampling site in Hanimaadhoo, caused by long-range transport from south and Southeast Asia, whereas the southern sampling site, Gan, was not subject to as much continental inflow. The polluted period began in mid-November and lasted through the remainder of the sampling period. Fine particulate matter during this time was characterized by relatively high concentrations of aerosol mass and elemental carbon. Concentrations of water-soluble potassium, sulfate, levoglucosan, polyaromatic hydrocarbons, aliphatic diacids, aromatic diacids, and trace metals increased over the clean, transition, and polluted dry season. Organic speciation suggested that significant secondary organic aerosol formation occurred during the polluted dry season, meaning that traditional methods of source identification relying on fixed elemental and organic carbon ratios between source and receptors are not sufficient. Well-studied molecular markers for combustion sources were not adequate in fully attributing elemental carbon over the northern Indian Ocean to specific sources. Further source profiling of south and Southeast Asian biofuels and fossil fuels is recommended. A receptor-based positive matrix factorization model was applied to fine particulate matter trace metal measurements and showed that biofuel burning and fossil fuel combustion were equally important sources of elemental carbon during the polluted dry season.

polluted oceanic regions, the EC mass exceeds 0.5 m gm 3 , the OC mass exceeds 2 m gm 3 and sulfate mass exceeds 10 m gm 3 from the surface to 3 km. The brown clouds also have strong seasonal dependence. In the tropics the seasonal dependence is driven by pollution accumulating during the dry seasons, December to February in Northern Hemisphere tropics and June to August in Southern Hemisphere tropics. In the extratropics the pollution peaks during the summer. The brown cloud problem is not restricted to the tropical regions. Over the eastern half of US and western Europe the AODs exceeds 0.2 and absorption AODs exceed 0.02. Brown clouds also extend well into the western Pacific Ocean, the Indian Ocean reaching as far south as 60S and the eastern Atlantic Ocean. The largest total SO2 emission occurs over China and US, while SO2 emission per unit surface area is maximum over Germany and England. The largest total EC and OC emissions occur over China, but the largest OC emission per unit surface area occur over India. As a result, the maximum negative annual mean TOA direct forcing is over India and Germany. The surface annual-diurnal mean dimming over the regional hot spots is of the order of 10 W m 2 and 20 W m 2 over megacity hotpots.

Fine particle organic carbon in Delhi, Mumbai, Kolkata, and Chandigarh is speciated to quantify sources contributing to fine particle pollution. Gas chromatography/mass spectrometry of 29 particle-phase organic compounds, including n-alkanes, polycyclic aromatic hydrocarbons (PAHs), hopanes, steranes, and levoglucosan along with quantification of silicon, aluminum, and elemental carbon are used in a molecular-marker based source apportionment model to quantify the primary source contributions to the PM_(2.5) mass concentrations for four seasons in three sites and for the summer in Chandigarh. Five primary sources are identified and quantified: diesel engine exhaust, gasoline engine exhaust, road dust, coal combustion, and biomass combustion. Important trends in the seasonal and spatial patterns of the impact of these five sources are observed. On average, primary emissions from fossil fuel combustion (coal, diesel, and gasoline) are responsible for about 25–33% of PM_(2.5) mass in Delhi, 21–36% in Mumbai, 37–57% in Kolkata, and 28% in Chandigarh. These figures can be compared to the biomass combustion contributions to ambient PM_(2.5) of 7–20% for Delhi, 7–20% for Mumbai, 13–18% for Kolkata, and 8% for Chandigarh. These measurements provide important information about the seasonal and spatial distribution of fine particle phase organic compounds in Indian cities as well as quantifying source contributions leading to the fine particle air pollution in those cities.

[1] A significant fraction of the fine particulate matter in Hong Kong is made up of organic carbon. In order to quantitatively assess the contributions of various sources to carbonaceous aerosol in Hong Kong, a chemical mass balance (CMB) receptor model in combination with organic tracers was employed. Organic tracers including n-alkanes, polycyclic aromatic hydrocarbons (PAHs), steranes, hopanes, resin acids, cholesterol, levoglucosan, and picene in PM2.5 collected from three air monitoring sites located at roadside, urban, and rural areas in Hong Kong are quantified using gas chromatography-mass spectrometry (GC/MS) in the present study. Analyses of some overlapping species from two separate laboratories will be compared for the first time. Spatial and seasonal source contributions to organic carbon (OC) in PM2.5 from up to nine air pollution sources are assessed, including diesel engine exhaust, gasoline engine exhaust, meat cooking, cigarette smoke, biomass burning, road dust, vegetative detritus, coal combustion, and natural gas combustion. Diesel engine exhaust dominated fine organic carbon in Hong Kong (57 ± 13% at urban sites and 25 ± 2% at the rural site). Other sources that play an important role are meat cooking and biomass burning, which can account for as much as 14% of fine organic carbon. The primary sources identified by this technique explained 49%, 79%, and 94% of the measured fine organic carbon mass concentration at the rural, the urban, and the roadside sites, respectively. The unexplained fine OC is likely due to secondary organic aerosol formation.

[1] Spatial variations of source contributions to fine organic carbon (OC) and fine particles in the southeastern United States were investigated using molecular marker-based chemical mass balance modeling (CMB-MM) and carbon isotope analysis. Nine primary emission sources were resolved with wood combustion (average 1.73 μg m−3, 23 ± 14% of measured OC) being the most dominant contributor to OC, followed by gasoline engine exhaust (0.45 μg m−3, 6.1 ± 6.2% of OC), diesel engine exhaust (0.43 μg m−3, 4.8 ± 4.1% of OC), and meat cooking (0.30 μg m−3, 4.1 ± 2.6% of OC). Measurable contributions from vegetative detritus, cigarette smoke, road dust, and natural gas exhaust were found. The impact of coke facilities was estimated for the first time in Birmingham, Alabama, and contributed 0.52 μg m−3 on average to fine OC. The unexplained OC accounted for 54 ± 26% of measured OC, possibly because of contributions from secondary OC, other unidentified primary sources and the possible positive artifact of OC. The urban excess of OC from diesel exhaust, gasoline exhaust and meat cooking can be seen from the results of the urban-rural pair in Alabama. Detailed chemical analysis revealed the wood burning episode at the rural site and an episode of secondary formation in the study region. The 14C analysis, a tool to study the relative contributions of contemporary and fossil carbon contents of fine particles, agreed well with the CMB-MM analysis. Both reflected a higher fossil fraction of carbon at urban sites especially in Birmingham, Alabama.

Each spring, Beijing, China, experiences dust storms which cause high particulate matter concentrations. Beijing also has many anthropogenic sources of particulate matter including the large Capitol Steel Company. On the basis of measured size segregated, speciated particulate matter concentrations, and calculated back trajectories, three types of pollution events occurred in Beijing from 22 March to 1 April 2001: dust storms, urban pollution events, and an industrial pollution event. For each event type, the source of each measured element is determined to be soil or anthropogenic and profiles are created that characterize the particulate matter composition. Dust storms are associated with winds traveling from desert regions and high total suspended particle (TSP) and PM2.5 concentrations. Sixty-two percent of TSP is due to elements with oxides and 98% of that is from soil. Urban pollution events have smaller particulate concentrations but 49% of the TSP is from soil, indicating that dust is a major component of the particulate matter even when there is not an active dust storm. The industrial pollution event is characterized by winds from the southwest, the location of the Capitol Steel Company, and high particulate concentrations. PM2.5 mass and acidic ion concentrations are highest during the industrial pollution event as are Mn, Zn, As, Rb, Cd, Cs and Pb concentrations. These elements can be used as tracers for industrial pollution from the steel mill complex. The industrial pollution is potentially more detrimental to human health than dust storms due to higher PM2.5 concentrations and higher acidic ion and toxic particulate matter concentrations.

increased by an order of magnitude from 0.03 to 0.47 � g/m 3 . These measurements suggest a large increase in the aerosol radiative forcing of the region with the arrival of the dry monsoon.

[1] Iron, and in particular water soluble iron, is an important trace nutrient in the surface ocean, and therefore an important component in the global carbon cycle. Deposition of Asian aerosol is thought to be a primary source of water soluble iron in the northern Pacific. Analysis of aerosol samples obtained during the Aerosol Characterization Experiment (ACE)–Asia field campaign from Jeju Island, Korea, which intercepts the outflow from the Asian continent, shows that water soluble iron is not dominated by mineral dust sources even during large dust storms. Instead, our analysis indicates that particulate soluble iron and elemental carbon concentrations are correlated. This leads to the conclusion that soluble iron in this region is strongly connected to anthropogenic activity and not connected to mineral dust emissions, especially if the budget averaged over annual time scales is considered.

[1] An instrument for on-line continuous measurement of the water-soluble organic carbon (WSOC) component of aerosol particles is described and results from an urban site in St. Louis are presented. A Particle-into-Liquid Sampler impacts ambient particles, grown to large water droplets, onto a plate and then washes them into a flow of purified water. The resulting liquid is filtered and the carbon content quantified by a Total Organic Carbon analyzer providing continuous six-minute integral measurements with a detection limit of 0.1 μg C/m3. Summer and fall measurements of WSOC and organic carbon (OC) indicated WSOC/OC ratio typically ranged from 0.40 to 0.80. A diurnal variation in WSOC/OC that correlated with ozone was observed over extended periods in June; however, other periods in August had no correlation. The results suggested that WSOC was composed of a complex mixture of compounds that may contain a significant fraction from secondary organic aerosol formation.

in both sap and ssp, resulting from diurnal changes in the mixing height as well as from local combustion sources in the morning and dust sources in the afternoon. Two distinct populations of aerosol mass scattering efficiencies Escat_2.5, one for aerosols dominated by desert dust (� 1.0 m 2 g � 1 ) and the other for aerosols composed primarily of local pollutants (� 3.0 m 2 g � 1 ), are observed. During the field study there were three significant dust events that occurred for, on average, several days at a time. The most significant dust storm resulted in a 24-hour-average PM2.5 concentration (mass concentration of particles having aerodynamic diameters less than 2.5 mm) of 453 m gm � 3 and a peak ssp of 2510 Mm � 1 on 8 April. The mean PM2.5 mass concentration during the dust storm periods is approximately 169 m gm � 3 , about 4 times greater than the mean value of 44 m gm � 3 observed during local pollution periods. When local pollution is the dominant source of fine particulate mass, organic matter (OM) is the major chemical component, contributing 41% to the PM2.5 mass, followed by crustal material (29%), sulfate (17%), and elemental carbon (EC) (13%). During sand storm periods, � 51% of PM2.5 mass is crustal material, followed by CO3� (11%) and OM (9.5%). The element enrichment factors indicate that coal combustion, biomass burning, and mobile source emissions are important local pollution sources. Overall, our results indicate that in addition to dust, local pollution also has a significant influence on aerosol properties in the region. INDEX TERMS: 0305 Atmospheric Composition and Structure: Aerosols and particles (0345, 4801); 0345 Atmospheric Composition and Structure: Pollution—urban and regional (0305); 0360 Atmospheric Composition and Structure: Transmission and scattering of radiation; 9320 Information Related to Geographic Region: Asia; KEYWORDS: aerosol, dust, ACE-Asia

[1] Throughout South Asia biomass is commonly used as a fuel source for cooking and heating homes. The smoke from domestic use of these fuels is expected to be a major source of atmospheric particulate matter in the region and needs to be characterized for input in regional source apportionment models and global climate models. Biomass fuel samples including coconut leaves, rice straw, jackfruit branches, dried cowdung patties, and biomass briquettes manufactured from compressed biomass material were obtained from Bangladesh. The fuel samples were burned in a wood stove to collect and characterize the particulate matter emissions. The bulk chemical composition including total organic and elemental carbon, sulfate, nitrate, ammonium and chloride ions, and bulk elements such as potassium and sodium did not show conclusive differences among the biomass samples tested. Unique features, however, exist in the detailed organic characterization of the combustion smoke from the different sources. The organic compound fingerprints of the particulate matter are shown to be distinct from one another and distinct from North American wood fuels. Fecal stanols including 5b-stigmastanol, coprostanol, and cholestanol are found to be good molecular markers for the combustion of cowdung. Additionally, the patterns of methoxyphenols and plant sterols provide a unique signature for each biomass sample and are conducive as source apportionment tracers. INDEX TERMS: 0305 Atmospheric Composition and Structure: Aerosols and particles (0345, 4801); 0345 Atmospheric Composition and Structure: Pollution—urban and regional (0305); 0399 Atmospheric Composition and Structure: General or miscellaneous; 1699 Global Change: General or miscellaneous; KEYWORDS: biomass aerosol, molecular marker, organic

[1] Measurements of elemental carbon (EC) during the Asian Pacific Regional Aerosol Characterization Experiment (ACE-Asia) show that significant amounts of EC were found in the coarse particle phase during yellow sand events. Coagulation during long-range transport is consistent with this observation. The daily averaged specific mass absorption efficiencies of EC were calculated, yielding values of 12.6 ± 2.6 and 14.8 ± 2.3 m2/g for PM10 (particulate matter