Aerosol Black Carbon Concentrations Research Articles

Potential Impacts on Ozone and Climate From a Proposed Fleet of Supersonic Aircraft

AbstractThere has been renewed interest in developing commercial supersonic transport aircraft due to the increased overall demands by the public for air travel, the aspiration for more intercontinental travel, and the desire for shorter flight times. Various companies and academic institutions have been actively considering the designs of such supersonic aircraft. As these new designs are developed, the environmental impact on ozone and climate of these fleets need to be explored. This study examines one such proposed commercial supersonic fleet of 55‐seater that is projected to fly at Mach 2.2, corresponding to cruise altitudes of 17–20 km, and which would burn 122.32 Tg of fuel and emit 1.78 Tg of NOx each year. Our analyses indicate this proposed fleet would cause a 0.74% reduction in global column ozone (∼2 Dobson Units), which is mainly attributed to the large amounts of nitrogen oxides released in the atmosphere from the supersonic aircraft. The maximum ozone loss occurs at the tropics in the fall season, with a reduction of −1.4% in the total column ozone regionally. The stratospheric‐adjusted radiative forcing on climate from this fleet was derived based on changes in atmospheric concentrations of ozone (59.5 mW/m2), water vapor (10.1 mW/m2), black carbon (−3.9 mW/m2) and sulfate aerosols (−20.3 mW/m2), resulting in a net non‐CO2, non‐contrail forcing of 45.4 mW/m2, indicating an overall warming effect.

Effects of transport on a biomass burning plume from Indochina during EMeRGe-Asia identified by WRF-Chem

Abstract. The Indochina biomass burning (BB) season in springtime has a substantial environmental impact on the surrounding areas in Asia. In this study, we evaluated the environmental impact of a major long-range BB transport event on 19 March 2018 (a flight of the High Altitude and Long Range Research Aircraft (HALO; https://www.halo-spp.de, last access: 14 February 2023) research aircraft, flight F0319) preceded by a minor event on 17 March 2018 (flight F0317). Aircraft data obtained during the campaign in Asia of the Effect of Megacities on the transport and transformation of pollutants on the Regional to Global scales (EMeRGe) were available between 12 March and 7 April 2018. In F0319, results of 1 min mean carbon monoxide (CO), ozone (O3), acetone (ACE), acetonitrile (ACN), organic aerosol (OA), and black carbon aerosol (BC) concentrations were up to 312.0, 79.0, 3.0, and 0.6 ppb and 6.4 and 2.5 µg m−3, respectively, during the flight, which passed through the BB plume transport layer (BPTL) between the elevation of 2000–4000 m over the East China Sea (ECS). During F0319, the CO, O3, ACE, ACN, OA, and BC maximum of the 1 min average concentrations were higher in the BPTL by 109.0, 8.0, 1.0, and 0.3 ppb and 3.0 and 1.3 µg m−3 compared to flight F0317, respectively. Sulfate aerosol, rather than OA, showed the highest concentration at low altitudes (<1000 m) in both flights F0317 and F0319 resulting from the continental outflow in the ECS. The transport of BB aerosols from Indochina and its impacts on the downstream area were evaluated using a Weather Research Forecasting with Chemistry (WRF-Chem) model. The modeling results tended to overestimate the concentration of the species, with examples being CO (64 ppb), OA (0.3 µg m−3), BC (0.2 µg m−3), and O3 (12.5 ppb) in the BPTL. Over the ECS, the simulated BB contribution demonstrated an increasing trend from the lowest values on 17 March 2018 to the highest values on 18 and 19 March 2018 for CO, fine particulate matter (PM2.5), OA, BC, hydroxyl radicals (OH), nitrogen oxides (NOx), total reactive nitrogen (NOy), and O3; by contrast, the variation of J(O1D) decreased as the BB plume's contribution increased over the ECS. In the lower boundary layer (<1000 m), the BB plume's contribution to most species in the remote downstream areas was <20 %. However, at the BPTL, the contribution of the long-range transported BB plume was as high as 30 %–80 % for most of the species (NOy, NOx, PM2.5, BC, OH, O3, and CO) over southern China (SC), Taiwan, and the ECS. BB aerosols were identified as a potential source of cloud condensation nuclei, and the simulation results indicated that the transported BB plume had an effect on cloud water formation over SC and the ECS on 19 March 2018. The combination of BB aerosol enhancement with cloud water resulted in a reduction of incoming shortwave radiation at the surface in SC and the ECS by 5 %–7 % and 2 %–4 %, respectively, which potentially has significant regional climate implications.

Source apportionment of black carbon aerosols in winter across China

Black carbon (BC) aerosols emitted from incomplete combustion of fossil fuels, biofuels, and biomass have significant effects on the environment and human health. Combustion-derived BC aerosols are an important component in haze pollution. High concentrations of BC aerosols were found in fine particulate matter (PM2.5) in China, and source apportionment was the strategy underpinning targeted mitigation actions. Here, we present a Bayesian statistical model, a three-dimensional array of a stable carbon isotope (δ13C) and the ratios of non-sea-salt K+ to BC (nss-K+/BC) and ΔBC/ΔCO that is a reasonably inexpensive and rapid way to constrain BC source apportionments. This study analyzed 551 daily PM2.5 samples collected in January 2018 in 18 large cities and at 1 remote site scattered across China. The results show that BC concentrations were generally higher in cities in northern China than they were in cities in southern China. Source apportionments indicate that BC in 44% of cities was mainly from liquid fuel combustion. In other sites, including 39% of cities, one suburban site, and one remote site, BC was mainly from biomass burning. These findings suggest that to improve air quality, the Chinese government should further strengthen controls on liquid fuel combustion and consider controlling biomass burning.

Estimation of hourly black carbon aerosol concentrations from glass fiber filter tapes using image reflectance-based method

Our method measures atmospheric BC concentrations by analyzing photos of particle deposits on glass-fiber filters. Post-analysis of beta attenuation monitor (BAM) tapes collected worldwide can be a valuable source for hourly BC data, particularly for Global South countries.

Investigating Drivers of Particulate Matter Pollution Over India and the Implications for Radiative Forcing With GEOS‐Chem‐TOMAS15

AbstractAmbient fine particulate matter (PM2.5) concentrations in India frequently exceed 100 μg/m3 during fall and winter pollution episodes. We use the GEOS‐Chem chemical transport model with the TwO‐Moment Aerosol Sectional microphysics scheme with 15 size bins (TOMAS15) to assess PM2.5 composition and impacts on radiation and cloud condensation nuclei (CCN) during pollution episodes as compared to the seasonal (October‐December) average. We conduct high resolution (0.25° × 0.3125°) nested‐domain simulations over India for short‐duration, high‐PM2.5 episodes in the fall of 2015 and 2017. The simulations capture the magnitude and spatial patterns of pollution episodes measured by surface monitors (r2PM2.5 = 0.69) although aerosol optical depth is underestimated. During the episodes, near‐surface organic matter (OM), black carbon (BC), and secondary inorganic aerosol concentrations increase from seasonal averages by up to 36, 7, and 7 μg/m3, respectively. Episodic aerosol increases enhance cooling by lowering the top‐of‐atmosphere clear‐sky direct radiative effect (DRETOA) during the 2015 episode (−6 W/m2), with a smaller impact during the 2017 episode (−1 W/m2). Differences in DRETOA reflect larger increases in scattering aerosols in the column during the 2015 episode (+17 mg/m2) than in 2017 (+13 mg/m2), while absorbing aerosol column enhancements are smaller (+3 mg/m2) in both years. Changes in shortwave radiation at the surface (SWsfc) are spatially similar to DRETOA and mostly negative during both episodes. CCN enhancements (0.2% supersaturation) during these episodes occur across the western Indo‐Gangetic Plain, coincident with higher PM2.5 concentrations. Changes in DRETOA, SWsfc, and CCN during high‐PM2.5 episodes may have implications for crops, the hydrologic cycle, and surface temperature.

Observational study of the influences of thermal and dynamic boundary layer on the vertical distribution of black carbon aerosol in ShouXian county in wintertime, 2016

Using vertical observation data of black carbon aerosol and meteorological parameters in the ShouXian area of Anhui Province from 14 December 2016 to 3 January 2017, the thermal and dynamic effects of the boundary layer on the vertical distribution structure of black carbon were studied. The results show that 1) of 82 vertical sounding profiles obtained during the observation period, there were 72 boundary layer sounding profiles dominated by heat and 10 profiles dominated by dynamics. 2) When thermal effects were dominant, the concentration of black carbon aerosol was significantly affected by diurnal changes in the boundary layer. In the unstable boundary layer, black carbon aerosol was uniformly distributed in the vertical direction; during the transition from an unstable to a stable boundary layer, the concentrations of black carbon aerosol were significantly higher in the lower layer than in the upper layer; in the stable boundary layer, the concentrations of black carbon aerosol decreased continuously with height; and during the transition from a stable to an unstable boundary layer, the black carbon aerosol concentrations exhibited high values in the upper layer, with the concentration difference reaching 4 μg m−3. 3) When the dynamic effect was dominant, the structure of the vertical distribution of black carbon aerosol was affected by wind and by diurnal changes in the boundary layer simultaneously. The high winds (>4 m/s) removed the black carbon aerosol. In the unstable boundary layer, the black carbon aerosol uniformly distributed in the vertical direction had significantly lower concentrations in the high-wind range; when stable boundary layers occurred and during transitions from stable to unstable boundary layers, the black carbon aerosol concentrations were higher in the lower layer and lower in the upper layer. The stratification was more obvious than that observed under thermal control.

Numerical simulation of the impact of COVID-19 lockdown on tropospheric composition and aerosol radiative forcing in Europe

Abstract. Aerosols influence the Earth's energy balance directly by modifying the radiation transfer and indirectly by altering the cloud microphysics. Anthropogenic aerosol emissions dropped considerably when the global COVID-19 pandemic resulted in severe restraints on mobility, production, and public life in spring 2020. We assess the effects of these reduced emissions on direct and indirect aerosol radiative forcing over Europe, excluding contributions from contrails. We simulate the atmospheric composition with the ECHAM5/MESSy Atmospheric Chemistry (EMAC) model in a baseline (business-as-usual) and a reduced emission scenario. The model results are compared to aircraft observations from the BLUESKY aircraft campaign performed in May–June 2020 over Europe. The model agrees well with most of the observations, except for sulfur dioxide, particulate sulfate, and nitrate in the upper troposphere, likely due to a biased representation of stratospheric aerosol chemistry and missing information about volcanic eruptions. The comparison with a baseline scenario shows that the largest relative differences for tracers and aerosols are found in the upper troposphere, around the aircraft cruise altitude, due to the reduced aircraft emissions, while the largest absolute changes are present at the surface. We also find an increase in all-sky shortwave radiation of 0.21 ± 0.05 W m−2 at the surface in Europe for May 2020, solely attributable to the direct aerosol effect, which is dominated by decreased aerosol scattering of sunlight, followed by reduced aerosol absorption caused by lower concentrations of inorganic and black carbon aerosols in the troposphere. A further increase in shortwave radiation from aerosol indirect effects was found to be much smaller than its variability. Impacts on ice crystal concentrations, cloud droplet number concentrations, and effective crystal radii are found to be negligible.

Effect of COVID-19 epidemic-led lockdowns on aerosol black carbon concentration, sources and its radiation effect in northeast India

The COVID-19 epidemic-led lockdown (LD) from March 25 to May 31, 2020, had a different level of impact on air quality in the ecologically sensitive region of northeast India, even though the restriction on main anthropogenic activities was expected to reduce particulate matter concentration. The daily average black carbon concentration measured at 880 nm (BC880) was 1.5–15.6 μg m−3 (mean: 5.75±4.24 μg m−3) during the measurement period. It was 9.29±4.11 μg m−3 during pre-LD (February 12–March 21), 4.70±0.95 μg m−3 during LD1 (March 25–April 14), 3.41±0.56 μg m−3 during LD2 (April 15–May 3), 3.69±1.50 μg m−3 during LD3 (May 4–17), 2.94±0.93 μg m−3 during LD4 (May 18–31), and 6.56±5.35 μg m−3 during the Post-LD (June 6–July 3) of 2020. It decreased up to 68% during the lockdowns. The source apportionment based on an improved method showed a significant improvement in the contribution of BC880 sources. The radiation effect determined by Angstrom Absorption Exponent showed that brown carbon accounted for 25% of the aerosol light absorption at 370 nm during the lockdown period. Relative humidity correlates substantially with BC880, while rainfall, temperature, and solar radiation were negatively correlated. The bivariate analysis showed the dominance of local emissions in the BC880 concentrations.Research highlights Black carbon concentration decreased up to 68% during the different phases of lockdown.BC associated with fossil fuel was 51–78%, and biomass burning was 22–49%.The fraction of fossil fuel and biomass burning in whole BC fallen to 0.73 and 0.65 during the lockdowns.Air quality improved by about 47–58% on the 4th and 7th day of lockdown.Brown carbon and meteorological parameters significantly impacted aerosol light absorption in this region.Supplementary InformationThe online version contains supplementary material available at 10.1007/s12040-022-01883-4.

INTRA-SEASONAL AND SEASONAL TRANSITION VARIATION OF AEROSOL BLACK CARBON OVER HIGH ALTITUDE REGION OF SOUTHERN INDIA, OOTY, TAMILNADU

The Black carbon is the aerosol particle that has been produced from the incomplete combustion of carbonaceous fuels. The concentration of the Aerosol Black Carbon (ABC) was measured by using the Aethalometer (Magee Scientific Model AE-31) at high altitude region, Ooty. This study has measured the diurnal and seasonal variation of ABC concentration for the winter and transition month of March (winter to summer), 2021. They were also influenced by the local meteorological conditions. The average winter (January-February) and March month concentration were recorded as 0.89±0.26 μg m-3 and 1.46±0.62 μg m-3 respectively, and it shows significant variation at diurnally during the winter as well as in transition month. Aerosol Black carbon concentration attains the peak during evening hours (17:00 to 20:00 LT) in winter and follows the bimodal peaks in morning (09:00 LT) and late evening hour (21:00 LT) during March month. The ABC concentration was significantly related with the Aerosol optical depth which denotes that the ABC is one of the contributors to the atmospheric aerosols. The results showed that their nature tend to change with the local meteorological conditions and to the seasonal variation.

Equivalent Black Carbon Aerosol Properties and Their Relationship with the Heating Season in Urban Environments

Black carbon (BC) aerosols have a considerable impact on humans because they not only cause environmental pollution and reduce visibility but also harm human health. During the heating season in northern China, a large amount of coal is burned for heating, producing a large amount of BC. There are few studies on BC properties during the heating season. In this paper, BC is measured optically, so it is referred to as equivalent black carbon (EBC). This paper investigated EBC properties in depth during the heating and nonheating seasons of a typical urban environment in China with two years of EBC measurements. The results show that: (1) EBC aerosol concentrations during the heating season were significantly higher than those during the nonheating season. (2) The main sources of EBC aerosols throughout the year are liquid sources. During the heating season, solid sources (coal and biomass combustion) are dominant. (3) The proportion of brown carbon (BrC) produced by biomass energy during the heating season is greater than that during the nonheating season. (4) The resulting backward trajectory indicates that a large portion of the high EBC aerosol concentration sources originate from northern and northwestern China. Our results reveal that the characteristics and sources of EBC in the urban environment of northern China vary widely, suggesting that different measures should be taken to reduce BC aerosol concentrations during heating and nonheating seasons.

Hemispheric black carbon increase after the 13th-century Māori arrival in New Zealand.

New Zealand was among the last habitable places on earth to be colonized by humans1. Charcoal records indicate that wildfires were rare prior to colonization and widespread following the 13th- to 14th-century Māori settlement2, but the precise timing and magnitude of associated biomass-burning emissions are unknown1,3, as are effects on light-absorbing black carbon aerosol concentrations over the pristine Southern Ocean and Antarctica4. Here we used an array of well-dated Antarctic ice-core records to show that while black carbon deposition rates were stable over continental Antarctica during thepast two millennia, they were approximately threefold higher over the northern Antarctic Peninsula during the past 700 years. Aerosol modelling5 demonstrates that the observed deposition could result only from increased emissions poleward of 40°S-implicating fires in Tasmania, New Zealand and Patagonia-but only New Zealand palaeofire records indicate coincident increases. Rapid deposition increases started in 1297 (±30 s.d.) in the northern Antarctic Peninsula, consistent with the late 13th-century Māori settlement and New Zealand black carbon emissions of 36 (±21 2s.d.) Gg y-1 during peak deposition in the 16th century. While charcoal and pollen records suggest earlier, climate-modulated burning in Tasmania and southern Patagonia6,7, deposition in Antarctica shows that black carbon emissions from burning in New Zealand dwarfed other preindustrial emissions in these regionsduring the past 2,000 years, providing clear evidence of large-scale environmental effects associated with early human activities across the remote Southern Hemisphere.

Variability of black carbon aerosol concentrations and sources at a Mediterranean coastal region

To investigate the temporal variation of aerosol optical properties and evaluate the main emission sources of black carbon (BC) considering different seasons in a typical Mediterranean coastal environment, a field campaign was conducted during February–July 2019 at the Central Adriatic coastal area. Real-time measurements of aerosol light absorption were continuously obtained using an aethalometer while the Aethalometer model source apportionment data, optimized by using levoglucosan measurements, were evaluated against the modelling results of the LOTOS-EUROS chemical transport model. The measured mean equivalent BC mass concentration of 0.57 ± 0.64 μg m−3 was the lowest observed in the Mediterranean region. BC from fossil fuel (BCff) dominated the area throughout the study period with a maximum in winter and elevated levels by the approaching summer tourist season. Diel variability of BC concentrations from biomass burning (BCbb) was observed during stable winter conditions, with clear morning and evening concentration peaks, consistent with the profile of residential heating by wood burning. Up to 88% of BC concentrations were attributed to European emission sectors, with stationary source combustion, transportation, shipping and agriculture sectors being the most influential contributors. Source apportionment of BC highlighted that, in addition to biomass burning, small combustion fossil fuel sources, including land traffic and shipping, should be more strictly controlled in order to limit BC pollution in Mediterranean coastal areas. This study serves as a basis of comparison for future studies addressing air quality and pollution source apportionment in the Adriatic and/or the Mediterranean coastal regions in efforts of mitigation and adaptation to climate change.

Characteristics of CCN activation and cloud microphysics over the east coast of India during the Northeast Monsoon onset

Airborne observations conducted during the Northeast Monsoon onset as part of the Cloud Aerosol Interaction and Precipitation Enhancement Experiment (CAIPEEX 2011) are used to link the activation properties of aerosols with the observed cloud microphysics. This study illustrates the significant spatial variability in the aerosol spectrum, cloud condensation nuclei (CCN) activation characteristics, and the cloud droplet spectral properties over a coastal and an inland location. High concentrations of Aitken mode and black carbon aerosols were observed in the free troposphere and are attributed to the convectively transported smoke and aerosols from the coastal boundary layer. The assumption of an internally mixed organic and inorganic aerosol composition provided a better CCN closure over assumptions of either purely organic or purely inorganic aerosols. The coastal clouds were equally polluted as the inland clouds with high cloud droplet number concentrations near the cloud base. The vertical distribution of cloud droplet spectral characteristics was similar in both coastal and inland clouds. An increase in droplet number concentration up to 2 km above the cloud base indicated a prominent influence of submicron particles on the cloud microphysical parameters. Evidence for an enhanced concentration of supercooled drops above the freezing level up to temperatures below −12 °C is documented. The secondary ice production was evident through observations of graupel and snow particles. Heavy loading of aerosols near the cloud base leads to enhanced mixed-phase processes in these clouds.

Multi-year characterization of aerosol black carbon concentrations over a semiarid tropical site Udaipur.

Continuous and multi-year (2008-2012) measurements of black carbon (BC) mass concentrations (MBC), carried out from the semiarid tropical site Udaipur (24.6° N, 74° E, 580ma.s.l.) near the western Indian desert, are analyzed for their region-specific features. MBC varied over a wide range during the period of study, with the hourly mean values occurring as low as 0.09 to as high as 49.1μgm-3, with the multi-year average ~ 4.5 ± 2.6μgm-3. Annual variations showed the highest concentrations during November and December (winter seasonal mean = 7.4 ± 3.3μgm-3) and the lowest in the monsoon months of July and August (monsoon seasonal mean = 2.5 ± 2.2μgm-3). MBC showed significant inverse relationship with the planetary boundary layer height (ρ ~ - 0.50) as well as ventilation coefficient (ρ ~ - 0.72). Alike aforesaid atmospheric dynamic parameters, T, WS, and RH also possessed statistically significant negative correlations with monthly MBC. Enhancement in annual as well as diurnal amplitude in MBC during deficient monsoon years relative to excessive monsoon years have given marked indication of BC sink mechanism due to precipitation. Roles of long-range regional air pollutant transport also have been identified. Identical and consistent seasonal variation in percentage contribution of MBC with PM2.5 (varying from 2.6 to 9.1%) and absorption Angstrom exponent (αabs, monthly mean values varying from 0.77 ± 0.04 to 1.16 ± 0.08) gives evidence of substantial amount of enhanced anthropogenic source activities of fossil fuel incomplete combustion in post-monsoon and winter period.

Source attribution of Arctic black carbon and sulfate aerosols and associated Arctic surface warming during 1980–2018

Abstract. Observations show that the concentrations of Arctic sulfate and black carbon (BC) aerosols have declined since the early 1980s. Previous studies have reported that reducing sulfate aerosols potentially contributed to the recent rapid Arctic warming. In this study, a global aerosol–climate model (Community Atmosphere Model, version 5) equipped with Explicit Aerosol Source Tagging (CAM5-EAST) is applied to quantify the source apportionment of aerosols in the Arctic from 16 source regions and the role of aerosol variations in affecting changes in the Arctic surface temperature from 1980 to 2018. The CAM5-EAST simulated surface concentrations of sulfate and BC in the Arctic had a decrease of 43 % and 23 %, respectively, in 2014–2018 relative to 1980–1984 mainly due to the reduction of emissions from Europe, Russia and local Arctic sources. Increases in emissions from South and East Asia led to positive trends in Arctic sulfate and BC in the upper troposphere. All aerosol radiative impacts are considered including aerosol–radiation and aerosol–cloud interactions, as well as black carbon deposition on snow- and ice-covered surfaces. Within the Arctic, sulfate reductions caused a top-of-atmosphere (TOA) warming of 0.11 and 0.25 W m−2 through aerosol–radiation and aerosol–cloud interactions, respectively. While the changes in Arctic atmospheric BC has little impact on local radiative forcing, the decrease in BC in snow and ice led to a net cooling of 0.05 W m−2. By applying climate sensitivity factors for different latitudinal bands, global changes in sulfate and BC during 2014–2018 (with respect to 1980–1984) exerted a +0.088 and 0.057 K Arctic surface warming, respectively, through aerosol–radiation interactions. Through aerosol–cloud interactions, the sulfate reduction caused an Arctic warming of +0.193 K between the two time periods. The weakened BC effect on snow–ice albedo led to an Arctic surface cooling of −0.041 K. The changes in atmospheric sulfate and BC outside the Arctic produced a total Arctic warming of +0.25 K, the majority of which is due to the midlatitude changes in radiative forcing. Our results suggest that changes in aerosols over the midlatitudes of the Northern Hemisphere have a larger impact on Arctic temperature than other regions through enhanced poleward heat transport. The combined total effects of sulfate and BC produced an Arctic surface warming of +0.297 K, explaining approximately 20 % of the observed Arctic warming since the early 1980s.

Black carbon aerosols over a high altitude station, Mahabaleshwar: Radiative forcing and source apportionment

Observations of Black Carbon (BC) aerosol concentrations were carried at Mahabaleshwar, a high altitude station in southwest India during March 2017–February 2019 using an Aethalometer (AE42) from Magee Scientific. BC concentration at Mahabaleshwar, varied from 0.016 μg/m3 to 16.03 μg/m3, with an average of 1.56 ± 0.88 μg/m3, indicating significant burden of these absorbing aerosols even at the free tropospheric altitudes (1348 m AMSL) as the station height remains above the Mixing Layer Height (MLH) throughout the year (MLH varies from 60 to 1293.6 m). BC is found to exhibit strong seasonal variation with the maximum concentration during winter and minimum during monsoon. The concentrations of BC, BC from fossil fuel (BCff), and BC from biomass burning (BCbb) exhibit diurnal variation with maximum values in the morning and evening hours and lower values around the afternoon due to the changes in the mixing layer height. The BCff and BCbb show the maximum value in winter (BCff: 1.47 μg/m3, BCbb: 0.69 μg/m3) which may be due to more biomass burning activity in the surrounding area along with the lower atmospheric temperatures and wind speeds which trap the pollution near the surface. However, in summer and post-monsoon the BCff remains around 1.0 μg/m3 and BCbb remains around 0.4 μg/m3. The lowest values of BCff (0.47 μg/m3) and BCbb (0.15 μg/m3) are exhibited in monsoon. Large negative radiative forcing was observed at the surface (SUF) and at top of atmosphere (TOA) whereas that at the atmosphere (ATM) was positive during all the seasons for both composite aerosol and without BC scenarios thus inferring to the significant cooling at SUF and warming at ATM leading to high atmospheric heating rates. Overall, the contribution of BC to the total atmospheric aerosol radiative forcing (ARF) was found to be 43% for the whole observational period. Temporal variations of MLH, BCff, and BCbb along with meteorological parameters and bivariate analysis of winds with respect to BC have been also discussed.

The Observation Path Problems and the Formation Conditions of the Elevated Layer of Black Carbon Aerosol

Studies on the detection of layers with elevated black carbon aerosol (BC) concentrations and the formation conditions of these layers help understand the vertical distribution of BC concentrations, which will provide a basis for the assessment of climate effects and early pollution warnings. By using the Weather Research and Forecasting with Chemistry (WRF-Chem) numerical model, we performed a numerical simulation analysis on the authenticity of strongly elevated BC concentration layers that were detected by an aircraft in the mixing layer over Harbin, China, which is a high-emission area, on a clear sunny afternoon in the early heating period of 2016. We then discuss possible problems and solutions when non-vertical paths are used to detect the vertical distribution of BC concentrations. Finally, we discuss the favorable conditions for the formation of elevated BC concentration layers by a weak vertical flow based on the simulation. The modeling results show that the horizontal variability of BC concentration in the mixing layer in the observation area in Harbin was sufficiently large during the measurement. This produced a false elevated layer, as detected by the aircraft during one round of spiral flight in the mixing layer. The root mean square of the horizontal distribution of BC concentration did not change with height in the mixing layer during the daytime, but it decreased with the thickness of the mixing layer and was higher in the mixing layer than in the free atmosphere. Therefore, the thinner the mixing layer, in which the vertical distribution of the BC concentration is detected in an inclined path, the stronger interference of the horizontal variability on the detected results. In the daytime, due to strong turbulence in the mixing layer, weak vertical uplift is not favorable for the occurrence of elevated BC concentration layers in the mixing layer. In the nighttime, if weak vertical uplift is well-matched with the BC concentration or its vertical gradient, elevated BC concentration layers can be formed in the atmosphere. Compared with upper layers far from the ground, nighttime elevated layers are easier to form in lower layers near the ground because high BC concentrations or large vertical gradients are more likely to occur in the lower layers. Both cases facilitate the occurrence of large vertical upward transport rates of BC.

How emissions uncertainty influences the distribution and radiative impacts of smoke from fires in North America

Abstract. Fires and the aerosols that they emit impact air quality, health, and climate, but the abundance and properties of carbonaceous aerosol (both black carbon and organic carbon) from biomass burning (BB) remain uncertain and poorly constrained. We aim to explore the uncertainties associated with fire emissions and their air quality and radiative impacts from underlying dry matter consumed and emissions factors. To investigate this, we compare model simulations from a global chemical transport model, GEOS-Chem, driven by a variety of fire emission inventories with surface and airborne observations of black carbon (BC) and organic aerosol (OA) concentrations and satellite-derived aerosol optical depth (AOD). We focus on two fire-detection-based and/or burned-area-based (FD-BA) inventories using burned area and active fire counts, respectively, i.e., the Global Fire Emissions Database version 4 (GFED4s) with small fires and the Fire INventory from NCAR version 1.5 (FINN1.5), and two fire radiative power (FRP)-based approaches, i.e., the Quick Fire Emission Dataset version 2.4 (QFED2.4) and the Global Fire Assimilation System version 1.2 (GFAS1.2). We show that, across the inventories, emissions of BB aerosol (BBA) differ by a factor of 4 to 7 over North America and that dry matter differences, not emissions factors, drive this spread. We find that simulations driven by QFED2.4 generally overestimate BC and, to a lesser extent, OA concentrations observations from two fire-influenced aircraft campaigns in North America (ARCTAS and DC3) and from the Interagency Monitoring of Protected Visual Environments (IMPROVE) network, while simulations driven by FINN1.5 substantially underestimate concentrations. The GFED4s and GFAS1.2-driven simulations provide the best agreement with OA and BC mass concentrations at the surface (IMPROVE), BC observed aloft (DC3 and ARCTAS), and AOD observed by MODIS over North America. We also show that a sensitivity simulation including an enhanced source of secondary organic aerosol (SOA) from fires, based on the NOAA Fire Lab 2016 experiments, produces substantial additional OA; however, the spread in the primary emissions estimates implies that this magnitude of SOA can be neither confirmed nor ruled out when comparing the simulations against the observations explored here. Given the substantial uncertainty in fire emissions, as represented by these four emission inventories, we find a sizeable range in 2012 annual BBA PM2.5 population-weighted exposure over Canada and the contiguous US (0.5 to 1.6 µg m−3). We also show that the range in the estimated global direct radiative effect of carbonaceous aerosol from fires (−0.11 to −0.048 W m−2) is large and comparable to the direct radiative forcing of OA (−0.09 W m−2) estimated in the Fifth Assessment Report (AR5) of the Intergovernmental Panel on Climate Change (IPCC). Our analysis suggests that fire emissions uncertainty challenges our ability to accurately characterize the impact of smoke on air quality and climate.

Spatial gradient of aerosol mass concentrations and size distributions over southeastern Arabian Sea and equatorial Indian Ocean during ICARB-2018

Continuous measurements of the mass concentrations of composite (MT) and Black Carbon (MB) aerosols were carried out on-board an Oceanographic Research Vessel (ORV) Sagar Kanya (cruise number – SK345) during its cruise (from 16 January to 13 February, 2018) over the southeastern Arabian Sea and equatorial Indian Ocean as a part of the Integrated Campaign for Aerosols, gases and Radiation Budget (ICARB-2018). In general, mass concentrations of aerosols during the cruise period of northern hemispheric winter were found to be high over the southeastern Arabian Sea (MT > 50 μg m−3; MB > 3 μg m−3), which gradually reduced to low values over the far oceanic regions of equatorial Indian Ocean (MT < 20 μg m−3; MB < 1 μg m−3). Aerosol mass size distributions were bimodal in nature having a prominent accumulation mode over both near coastal and far oceanic regions. Interestingly, BC mass fraction (FBC) also showed significant higher values (3.7%) at the far oceanic equatorial Indian Ocean, indicating the continental anthropogenic influence even in the remote environment. Over the near coastal locations of Arabian Sea, FBC increased significantly during the return phase of the cruise after a rainfall event. Considering latitudinal gradient between 15°N and 2°S, within the longitude sector of 65°E to 75°E, both MT and MB showed a scaling distance of 17.08° and 14.28° respectively. Investigation of the long-term temporal change of MT and MB over the experimental domain indicates that the values observed in the present study are significantly higher than those reported elsewhere two decades back, which is very significant over the Arabian Sea.

Abundance and Emission Flux of the Anthropogenic Iron Oxide Aerosols From the East Asian Continental Outflow

AbstractAnthropogenic iron oxide (FeOx) aerosols can affect atmospheric radiation, marine biogeochemistry, and human health. However, due to lack of observational data, their atmospheric abundance and emission flux are not well understood. In this study, we observed size‐resolved concentrations of FeOx (170–2100 nm) and black carbon (BC, 70–850 nm) aerosols at a remote site in the East China Sea in March 2016 using a modified single‐particle soot photometer (SP2). Light signals measured by the SP2 and particle morphology and compositions analyzed by a transmission electron microscope revealed that most of the observed FeOx aerosols are of anthropogenic origin. Clear correlations were found between mass concentrations of FeOx and BC (R2 = 0.717) and between FeOx and carbon monoxide (CO) (R2 = 0.718) in air masses from China, indicating that their emission sources are spatially similar. The correlation slopes of mass concentration (ng/m3) are ~0.3 and 0.0015, respectively. Based on the correlation slopes and emission inventories of BC and CO in China, we estimated emission flux of anthropogenic FeOx aerosols from China to be 0.21–0.49 FeTg/yr. Based on the observed size distribution and previous studies on mass fraction of FeOx and non‐FeOx, we also estimated emission flux of anthropogenic Fe (FeOx + non‐FeOx) in PM10 as 0.74–1.7 FeTg/yr. These emission fluxes from China are comparable to global emission fluxes in currently reported inventories of anthropogenic Fe (0.51–1.91 FeTg/yr). Our results suggest that the current emission inventories of anthropogenic Fe are underestimated.