Black Carbon Emission Rates Research Articles

Black carbon emissions from turbulent buoyant non-premixed flames representative of flares in the upstream oil and gas sector

Gas flaring, the pervasive oil and gas industry process of using turbulent buoyant non-premixed flames to destroy unwanted flammable gases, is an important global source of carbonaceous soot or black carbon (BC). However, experimental data and reliable models with which to predict these emissions over a range of flare gas compositions and operating conditions relevant to upstream oil and gas production sites (which account for 90 % of global flaring) do not exist. In the absence of alternatives, most official reporting and inventory estimates are based on single-valued emission factors that are known to be insufficient and inaccurate. This work addresses this gap through parametric experiments to measure BC emissions from vertical lab-scale flares at Reynolds and Froude number conditions directly relevant to flares at upstream oil and gas production sites, burning multicomponent C1-C7 alkane, CO2, and N2 flare gas mixtures typical of flares in North Dakota, USA and Alberta, Canada. Analysis reveals that BC emission rates fall under two different regimes corresponding to the transition buoyant and transition shear regimes of turbulent buoyant non-premixed flares previously proposed by Delichatsios based on visual flame observations and distinguished by the product of Reyolds number and the square of the fire Froude number. Within the transition buoyant regime, BC emissions are simply proportional to total volumetric fuel flowrate whereas within the transition shear regime BC emission are inversely proportional to the exit strain rate. For a narrow range of methane-dominated hydrocarbon mixtures relevant to upstream oil and gas flaring, empirical models are presented for each regime that reliably predict BC emissions scaled by the mean carbon number of the fuel. Though ultimately limited to the specific conditions considered in this study, these empirical models nevertheless are a significant improvement over existing, widely used single valued emission factors.

Black carbon emissions from modern automated cordwood stoves for space heating

AbstractWood burning stove design is improving as regulation become stricter for particulate matter emissions. This study describes results of black carbon (BC) emissions from three modern automated wood stoves when tested in common failure modes using a test protocol that included cold‐starts, high and low fuel loading densities, and use of overly large pieces of fuel. Emission sampling was performed using a dilution sampling system in tandem with an aethalometer to measure BC with high time resolution. Results show that the time‐weighted average BC emission rates were 0.91, 4.30, and 1.74 g/h for the three stoves tested (A, B, and C respectively), the values, both higher and lower than the United States 2020 certification test emission limit of 2.5 g/h. The results demonstrate good performance overall, given the rigorous nature of the testing protocol used. The aethalometer data showed that the performance was relatively poor during cold‐start, when the fuel was ignited and combusted without a coalbed, and when stoves failed to optimize air delivery due to specific loading and output conditions. During the cold‐start test section, the average BC emission rate was seven times higher than the overall average for Stove A, 10 times above the average for Stove B, and two times above the average emission rate for Stove C. Calculations of the Average Angstrom Absorption Exponent (AAE) of the exhaust aerosol showed little correlation with BC concentration. The results show that automation results in a quantifiable reduction in particular BC emissions.

Quantitative of instantaneous BC emissions based on vehicle specific power from real-world driving diesel trucks in China

In-depth exploration of the potential links between instantaneous black carbon (BC) emissions and driving parameters from real-world diesel trucks (DTs) is a key step toward development of a highly flexible vehicle emissions estimation system. In this study, we conducted real-world measurements on 22 DTs with mainstream types and emission standards, and obtained instantaneous data of BC emissions and vehicle driving. Since vehicle specific power (VSP) is an excellent surrogate for engine load, we characterize the instantaneous BC emissions and VSP distributions, and then establish links between VSP and fuel consumption, VSP and BC emission rates, VSP and BC emission factors (EFs), respectively. We find that BC emission rates of China V light-duty DTs installed with diesel particulate filter (DPF) are significantly lower (2 to 3 orders of magnitude) than those with China III and China IV. Frequent acceleration and deceleration of vehicles maybe the main reason leads to high BC emissions. The distribution of VSP is mainly concentrated in the ranges of −30 to 35 kW/t in the scope of this study. We find that VSP and BC EFs did not show a consistent pattern for all tested DTs, and BC EFs present obvious fluctuations with the VSP variation. The average fuel-based BC EFs vary by factors of 2.27–8.25 from the lowest to highest EFs. Through a fitting of the third-order polynomial function, we finally quantify and provide fitting formulas of BC EFs and VSP under more detailed categorization. Our results can provide important data support for accurate quantification of BC EFs, and even emission inventory calculations.

Impact of daily household activities on indoor PM2.5 and Black Carbon concentrations in Malta

In this study we present the outdoor and indoor particulate matter (PM) and Black Carbon (BC) measurements in a typical terraced house, located in an urban area in the island of Malta. The influence of different household activities on the indoor PM2.5 and BC levels were also analysed. The activities resulting in elevated indoor concentrations included sweeping, cooking (not grilling and frying), grilling and frying and burning of candle and incense sticks. Sweeping resulted in the highest PM2.5 concentration (283.14 μg m−3) while frying resulted in the lowest level (104.14 μg m−3). Burning of paraffin wax candles resulted in the largest increases in indoor BC concentration (62.2 μg m−3) while the lowest peaks corresponded to cooking and frying. We estimated average PM2.5 and BC emission rates for each indoor activity reaching 22.19 μg s−1 during sweeping and 2.46 μg s−1 during burning of paraffin candles and incense sticks and were sensitive to different ventilation rates. Given that people spend substantial time in the home environment, especially with a future where remote work is likely to be further facilitated, identifying the activities and sources which lead to elevated indoor pollutants is crucial to limit indoor exposure.

The determination of highly time-resolved and source-separated black carbon emission rates using radon as a tracer of atmospheric dynamics

Abstract. We present a new method for the determination of the source-specific black carbon emission rates. The methodology was applied in two different environments: an urban location in Ljubljana and a rural one in the Vipava valley (Slovenia, Europe), which differ in pollution sources and topography. The atmospheric dynamics was quantified using the atmospheric radon (222Rn) concentration to determine the mixing layer height for periods of thermally driven planetary boundary layer evolution. The black carbon emission rate was determined using an improved box model taking into account boundary layer depth and a horizontal advection term, describing the temporal and spatial exponential decay of black carbon concentration. The rural Vipava valley is impacted by a significantly higher contribution to black carbon concentration from biomass burning during winter (60 %) in comparison to Ljubljana (27 %). Daily averaged black carbon emission rates in Ljubljana were 210 ± 110 and 260 ± 110 µgm-2h-1 in spring and winter, respectively. Overall black carbon emission rates in Vipava valley were only slightly lower compared to Ljubljana: 150 ± 60 and 250 ± 160 µgm-2h-1 in spring and winter, respectively. Different daily dynamics of biomass burning and traffic emissions was responsible for slightly higher contribution of biomass burning to measured black carbon concentration, compared to the fraction of its emission rate. Coupling the high-time-resolution measurements of black carbon concentration with atmospheric radon concentration measurements can provide a useful tool for direct, highly time-resolved measurements of the intensity of emission sources. Source-specific emission rates can be used to assess the efficiency of pollution mitigation measures over longer time periods, thereby avoiding the influence of variable meteorology.

Effects of ambient temperature on regulated gaseous and particulate emissions from gasoline-, E10- and M15-fueled vehicles

Ambient temperature has substantial impacts on vehicle emissions, but the impacts may differ between traditional and alcohol gasolines. The objective of this study was to investigate the effects of temperature on gaseous and particulate emissions with both traditional and alcohol gasoline. Regulated gaseous, particle mass (PM), particle number (PN) and black carbon (BC) emissions from typical passenger vehicles were separately quantified with gasoline, E10 (10% ethanol and 90% gasoline by volume) and M15 (15% methanol and 85% gasoline by volume) at both 30°C and −7°C. The particulate emissions with all fuels increased significantly with decreased temperature. The PM emissions with E10 were only 48.0%–50.7% of those with gasoline at 30°C but increased to 59.2%–79.4% at −7°C. The PM emissions with M15 were comparable to those with gasoline at 30°C, but at −7°C, the average PM emissions were higher than those with gasoline. The variation trend of PN emissions was similar to that of PM emissions with changes in the fuel and temperature. At 30°C, the BC emissions were lower with E10 and M15 than with gasoline in most cases, but E10 and M15 might emit more BC than gasoline at −7°C, especially M15. The results of the transient PN and BC emission rates show that particulate emissions were dominated mainly by those emitted during the cold-start moment. Overall, the particulate emissions with E10 and M15 were more easily affected by ambient temperature, and the advantages of E10 and M15 in controlling particulate emissions declined as the ambient temperature decreased.

Real-time measurements of black carbon and other pollutant emissions from residential biofuel stoves in rural China

Biofuel stoves are an important source of black carbon (BC) emissions, which have adverse effects on the environment and human health, especially in rural areas. However, there have been only limited studies of BC emissions from residential biofuel stoves based on real-time measurements. In this study, a photo-acoustic extinctiometer (PAX)-based real-time measurement system was employed to monitor the emission characteristics of corncobs, corn stalks, cotton stalks and poplar branches in simple or improved stoves (with a total of 16 units) in Hebei Province, China. The real-time and phased emissions of BC, fine particulate matter (PM2.5), carbon monoxide (CO) and carbon dioxide (CO2) were assessed, and the effects of stove type and fuel on emissions were analyzed. Under the same conditions, polar branches were associated with the highest BC emission factors (EFs) of up to 2.64 ± 0.42 g kg−1, while the EFs for improved stoves were higher than those for simple stoves. During the ignition phase, BC emissions were found to be low, while the later addition of fuel dramatically increased emissions, followed by a gradual decrease until the next fuel addition. The phased results show that the flaming phase had the highest BC emission rate, the fuel addition phase was associated with the highest BC EF. The BC emission rates and EFs for the ignition, fuel addition, flaming and smoldering phases ranged from 0.0014–0.014, 0.11–6.32, 0.18–2.24 and 0.03–0.32 mg s−1, and from 0.04–0.18, 0.38–9.53, 0.45–3.55 and 0.12–1.01 g kg−1, respectively. This study assessed the BC emissions from residential biofuel stoves using a larger sample size than in prior work. The results increase our understanding of the BC emissions process, which is helpful in terms of improving the accuracy of BC EF estimations. The real-time measurement process described herein is also expected to provide new approaches to minimizing BC emissions.

Top-Down Determination of Black Carbon Emissions from Oil Sand Facilities in Alberta, Canada Using Aircraft Measurements.

Black carbon (BC) emissions from the Canadian oil sand (OS) surface mining facilities in Alberta were investigated using aircraft measurements. BC emission rates were derived with a top-down mass balance approach and were found to be linearly related to the volume of oil sand ore mined at each facility. Two emission factors were determined from the measurements; production-based BC emission factors were in the range of 0.6-1.7 g/tonne mined OS ore, whereas fuel-based BC emission factors were between 95 and 190 mg/kg-fuel, depending upon the facility. The annual BC emission, at 707 ± 117 tonnes/year for the facilities, was determined using the production-based emission factors and annual production data. Although this annual emission is in reasonable agreement with the BC annual emissions reported in the latest version of the Canadian national BC inventory (within 16%), the relative split between off-road diesel and stack sources is significantly different between the measurements and the inventory. This measurement evidence highlights the fact that the stack sources of BC may be overestimated and the off-road diesel sources may be underestimated in the inventory and points to the need for improved BC emission data from diesel sources within facilities.

Impact of particulate matter (PM) emissions from ships, locomotives, and freeways in the communities near the ports of Los Angeles (POLA) and Long Beach (POLB) on the air quality in the Los Angeles county

In this study, we evaluated the emission rates of ambient fine particulate matter (PM2.5) mass, particle number (PN), and black carbon (BC) from sources at the Ports of Los Angeles (POLA) and Long Beach (POLB), including ships, cargo-handling equipment (CHE), locomotives, and heavy-duty vehicles (HDVs) operating at the ports terminal, as well as from vehicles on the nearby freeways. We also evaluated the impact of these emissions on local air quality (i.e., within the “impact zone” of POLA and POLB), and on the air quality in the Los Angeles County. The impact zone of POLA and POLB was defined as the area confined by the I-105, I-110, and I-710 freeways, and the ports’ ship terminals. At the local scale, emission rates were dominated by the sources at the ports (i.e., ships, locomotives, CHE, and HDVs operating at the ports), with overall PM2.5, PN, and BC emission rates of 97.8 ± 9.8 kg day−1, 91.6 ± 10.6 × 1019 particles day−1, and 60.3 ± 5.3 kg day−1, respectively. Emission rates from sections of the abovementioned nearby freeways were considerably lower, with corresponding values of 8.4 ± 3.8 kg day−1 for PM2.5, 2.4 ± 1.3 × 1019 particles day−1 for PN, and 2.0 ± 1.6 kg day−1 for BC. However, at the scale of Los Angeles County, the emission rates from total freeways across the Los Angeles County were significantly higher than those of the POLA and POLB, with overall values of 506.9 ± 20.3 kg day−1 for PM2.5, 1.9 ± 0.4 × 1021 particles day−1 for PN, and 119.4 ± 10.2 kg day−1 for BC. Our findings illustrate the major impact of emissions from POLA and POLB on the air quality of communities in the vicinity of the port. However, across the Los Angeles County as a whole, freeway emissions become the most important source of PM2.5, PN, and BC emissions, with emission rates 2–5 times higher than those of source categories at POLA and POLB.

In-Use Performance and Durability of Particle Filters on Heavy-Duty Diesel Trucks.

Diesel particle filters (DPFs) are standard equipment on heavy-duty diesel trucks with 2007 and newer engines in the U.S. This study evaluates the performance and durability of these filters. Black carbon (BC) emission rates from several thousand heavy-duty trucks were measured at the Port of Oakland and Caldecott Tunnel over multiple years as California regulations accelerated the adoption of DPFs. As DPF use increased, fleet-average BC emissions decreased, and emission factor distributions became more skewed. Relative to 2004-2006 engines without filters, DPFs reduced BC emission rates by 65-70% for 2007-2009 engines and by >90% for 2010+ engines. Average BC emission rates for 2007-2009 engines increased by 50-67% in 2015 relative to measurements made 1-2 years earlier. Some trucks in this cohort have become high-emitters, indicating that some DPFs are no longer working well. At the Port, where DPFs were universal in 2015, high-emitting 2007-2009 engines (defined here as emitting >1 g BC kg-1) comprised 7% of the fleet but were responsible for 65% of the total BC emitted. These observations raise concerns about DPF durability and the prospects for fully mitigating adverse effects of diesel particulate matter on human health and the environment.

Assessment of biomass burning and fossil fuel contribution to black carbon concentrations in Delhi during winter

This study aims to assess the contribution of fossil-fuel combustion (BCff) and biomass (or wood) burning (BCwb) to wintertime black carbon (BC) concentrations in Delhi using the “Aethalometer model” approach. Continuous measurements using 7-wavelength Aethalometer (AE-33) were taken from December 2015 to February 2016 in Delhi downtown, as part of a multi-instrument research campaign, revealing high BC concentrations of 24.4 ± 12.2 μg m−3 (range from 3.2 to 59.9 μg m−3). The BCff contribution dominates with an average fraction of 72% at 880 nm, indicating an important contribution from biomass burning (28%). The daily-averaged Absorption Ångström Exponent (AAE370-880) varies between 1.08 and 1.46 due to changes in the BC emission rates, variations in the relative strength between fossil-fuel and wood-burning sources and mixing processes in the atmosphere. The average BCff/BCwb ratio is estimated as 2.90 ± 1.47 at 880 nm, while the BCwb contribution maximized in the evening hours due to enhanced wood burning for heating. The BC, BCff and BCwb concentrations exhibit remarkable diurnal variations with maximum values in the morning and evening/night hours and lower around noon, primarily driven by changes in the mixing-layer height. The highest BC, BCff and BCwb concentrations are associated with weak winds (<2 ms−1), revealing a dominance of local emission sources within the Delhi metropolitan area. A sensitivity analysis is performed by changing the wavelength pairs and the pre-assumed AAE values in order to evaluate the stability of the “Aethalometer model” in assessment of the BC source apportionment. The results reveal that the “Aethalometer model” is more sensitive in estimating the BCwb, while the changes in the BCff component are rather low.

The traffic emission-dispersion model for a Central-European city agrees with measured black carbon apportioned to traffic

The bottom-up traffic emission model EMISENS is used to calculate hourly black carbon (BC) and nitrogen oxides (NOx) emission rates on an average workday in Maribor (Slovenia), using emission factors that were previously determined with the on-road chasing measurements in Slovenia. From modeled NOx emission rates and in-situ NOx measurements we empirically determined the hourly dispersion of traffic emissions and applied it to model BC concentrations using BC emission rates. We compared the modeled BC concentrations with in-situ BC concentration measurements over three periods in winters 2011–2012 and 2012–2013, a total of 67 workdays. Measured BC concentrations were first apportioned to traffic using the top-down Aethalometer model. We found that the bottom-up modeled BC concentrations overestimated the top-down apportioned values by only 19%, 32% and 6% in each of the three investigated time periods, respectively. We did not find any influence of meteorology on the performance of the model. This is the first time that BC source apportionment results were used to evaluate traffic emissions calculated using the bottom-up modeling approach. We demonstrate that the two independent approaches yield similar results. We use thus validated emission inventory for evaluating different emission reduction scenarios. We show that excluding 10% of vehicles that are highest BC or NOx emitters would reduce the total BC or NOx emissions from traffic in Maribor by 39% and 33% respectively.

Estimates of spatially and temporally resolved constrained black carbon emission over the Indian region using a strategic integrated modelling approach

We estimated the latest spatially and temporally resolved gridded constrained black carbon (BC) emissions over the Indian region using a strategic integrated modelling approach. This was done extracting information on initial bottom-up emissions and atmospheric BC concentration from a general circulation model (GCM) simulation in conjunction with the receptor modelling approach. Monthly BC emission (83–364Gg) obtained from the present study exhibited a spatial and temporal variability with this being the highest (lowest) during February (July). Monthly BC emission flux was considerably high (>100kgkm−2) over the entire Indo-Gangetic plain (IGP), east and the west coast during winter months. This was relatively higher over the central and western India than over the IGP during summer months. Annual BC emission rate was 2534Gg y−1 with that over the IGP and central India respectively comprising 50% and 40% of the total annual BC emissions over India. A high relative increase was observed in modified BC emissions (more than five times the initial emissions) over the most part of the IGP, east coast, central/northwestern India. The relative predominance of monthly BC emission flux over a region (as depicted from z-score distribution maps) was inferred being consistent with the prevalence of region- and season-specific anthropogenic activity.

Field Measurements of Black Carbon Yields from Gas Flaring.

Black carbon (BC) emissions from gas flaring in the oil and gas industry are postulated to have critical impacts on climate and public health, but actual emission rates remain poorly characterized. This paper presents in situ field measurements of BC emission rates and flare gas volume-specific BC yields for a diverse range of flares. Measurements were performed during a series of field campaigns in Mexico and Ecuador using the sky-LOSA optical measurement technique, in concert with comprehensive Monte Carlo-based uncertainty analyses. Parallel on-site measurements of flare gas flow rate and composition were successfully performed at a subset of locations enabling direct measurements of fuel-specific BC yields from flares under field conditions. Quantified BC emission rates from individual flares spanned more than 4 orders of magnitude (up to 53.7 g/s). In addition, emissions during one notable ∼24-h flaring event (during which the plume transmissivity dropped to zero) would have been even larger than this maximum rate, which was measured as this event was ending. This highlights the likely importance of superemitters to global emission inventories. Flare gas volume-specific BC yields were shown to be strongly correlated with flare gas heating value. A newly derived correlation fitting current field data and previous lab data suggests that, in the context of recent studies investigating transport of flare-generated BC in the Arctic and globally, impacts of flaring in the energy industry may in fact be underestimated.

A global gas flaring black carbon emission rate dataset from 1994 to 2012.

Global flaring of associated petroleum gas is a potential emission source of particulate matters (PM) and could be notable in some specific regions that are in urgent need of mitigation. PM emitted from gas flaring is mainly in the form of black carbon (BC), which is a strong short-lived climate forcer. However, BC from gas flaring has been neglected in most global/regional emission inventories and is rarely considered in climate modeling. Here we present a global gas flaring BC emission rate dataset for the period 1994–2012 in a machine-readable format. We develop a region-dependent gas flaring BC emission factor database based on the chemical compositions of associated petroleum gas at various oil fields. Gas flaring BC emission rates are estimated using this emission factor database and flaring volumes retrieved from satellite imagery. Evaluation using a chemical transport model suggests that consideration of gas flaring emissions can improve model performance. This dataset will benefit and inform a broad range of research topics, e.g., carbon budget, air quality/climate modeling, and environmental/human exposure.

Black Carbon Emissions from the Bakken Oil and Gas Development Region

Black carbon (BC) emission rates from the Bakken oil-producing region of North Dakota have been quantified with a NOAA airborne single-particle soot photometer (SP2). Flights in May 2014 led to six measurements of the BC emission rate in the region. Oil and gas operations (associated flaring, diesel engines associated with pumping and drilling, and oil production-related transport), limited agricultural burning, and sparse urban/transport sector activity contribute to these emissions. The BC emission rate was 1400 ± 360 t year–1, implying that Bakken production activities are unlikely to contribute to large-scale biases in estimates of BC emissions. An upper limit on the BC emission factor from flaring based on these observations is 0.57 ± 0.14 g/m–3. Flaring BC was not associated with optically significant internally mixed non-BC material or with significant emissions of non-BC-containing primary aerosol. BC in the outflow from the region was also generally externally mixed.

The effects of emission control strategies on light-absorbing carbon emissions from a modern heavy-duty diesel engine

Control of atmospheric black carbon (BC) and brown carbon (BrC) has been proposed as an important pathway to climate change mitigation, but sources of BC and BrC are still not well understood. In order to better identify the role of modern heavy-duty diesel engines on the production of BC and BrC, emissions from a heavy-duty diesel engine operating with different emission control strategies were examined using a source dilution sampling system. The effect of a diesel oxidation catalyst (DOC) and diesel particulate filter (DPF) on light-absorbing carbon (LAC) was evaluated at three steady-state engine operation modes: idle, 50% speed and load, and 100% speed and load. LAC was measured with four different engine configurations: engine out, DOC out, DPF out, and engine out with an altered combustion calibration. BC and BrC emission rates were measured with the Aethalometer (AE-31). EC and BC emission rates normalized to the mass of CO2 emitted increased with increasing engine speed and load. Emission rates normalized to brake-specific work did not exhibit similar trends with speed and load, but rather the highest emission rate was measured at idle. EC and OC emissions were reduced by 99% when the DOC and DPF architecture was applied. The application of a DPF was equally effective at removing 99% of the BC fraction of PM, proving to be an important control strategy for both LAC and PM. BC emissions were unexpectedly increased across the DOC, seemingly due to a change aerosol optical properties. Removal of exhaust gas recirculation (EGR) flow due to simulated EGR cooler failure caused a large increase in OC and BrC emission rates at idle, but had limited influence during high load operation. LAC emissions proved to be sensitive to the same control strategies effective at controlling the total mass of diesel PM.Implications: In the context of black carbon emissions, very small emission rates of brown carbon were measured over a range of control technologies and engine operating conditions. During specific idle engine operation without EGR and adjusted fueling conditions, brown carbon can be formed in significant amounts, requiring careful management tactics. Control technologies for particulate matter are very effective for light-absorbing carbon, reducing black carbon emissions to near zero for modern engines equipped with a DPF. Efforts to control atmospheric brown carbon need to focus on other sources other than modern diesel engines, such as biomass burning.

The Pagami Creek smoke plume after long-range transport to the upper troposphere over Europe – aerosol properties and black carbon mixing state

Abstract. During the CONCERT 2011 field experiment with the DLR research aircraft Falcon, an enhanced aerosol layer with particle linear depolarization ratios of 6–8% at 532 nm was observed at altitudes above 10 km over northeast Germany on 16 September 2011. Dispersion simulations with HYSPILT suggest that the elevated aerosol layer originated from the Pagami Creek forest fire in Minnesota, USA, which caused pyro-convective uplift of particles and gases. The 3–4 day-old smoke plume had high total refractory black carbon (rBC) mass concentrations of 0.03–0.35 μg m−3 at standard temperature and pressure (STP) with rBC mass equivalent diameter predominantly smaller than 130 nm. Assuming a core-shell particle structure, the BC cores exhibit very thick (median: 105–136 nm) BC-free coatings. A large fraction of the BC-containing particles disintegrated into a BC-free fragment and a BC fragment while passing through the laser beam of the Single Particle Soot Photometer (SP2). In this study, the disintegration is a result of very thick coatings around the BC cores. This is in contrast to a previous study in a forest-fire plume, where it was hypothesized to be a result of BC cores being attached to a BC-free particle. For the high-altitude forest-fire aerosol layer observed in this study, increased mass specific light-absorption cross sections of BC can be expected due to the very thick coatings around the BC cores, while this would not be the case for the attached-type morphology. We estimate the BC mass import from the Pagami Creek forest fire into the upper troposphere/lower stratosphere (UTLS) region (best estimate: 25 Mg rBC). A comparison to black carbon emission rates from aviation underlines the importance of pyro-convection on the BC load in the UTLS region. Our study provides detailed information on the microphysics and the mixing state of BC in the forest-fire aerosol layer in the upper troposphere that can be used to better understand and investigate the radiative impact of such upper tropospheric aerosol layers.

Seasonal variations of the transport of black carbon and carbon monoxide from the Asian continent to the western Pacific in the boundary layer

[1] Continuous in situ measurements of the mass concentration of black carbon (BC) aerosols and mixing ratio of carbon monoxide (CO) were made at Cape Hedo on Okinawa Island, Japan, a remote site located in the East China Sea, from March 2008 to May 2009. For the first time, we show temporal variations of BC and CO at Hedo in Asian outflows throughout the year. Annual average concentrations of BC and CO were 0.29 μg m−3 and 150 ppbv, respectively. The origins of the observed air masses were determined by using 5-day back trajectories, suggesting that about 51% of the air masses arriving at Hedo were from the Chinese region during spring and winter, while about 78% of air masses were of maritime origin during summer. Because of the more frequent transport of Chinese air to Hedo in spring and winter, the average and background concentrations of BC and CO in these seasons were higher by about a factor of 2 than those in summer and fall. Air masses from north China made the largest contributions to elevating the BC levels at Hedo because of the high BC emission rate and frequency of transport. The observed ΔBC/ΔCO ratio systematically decreased with the decrease in model-calculated transport efficiency (TEBCcal). On the basis of this result, we derive region-specific ΔBC/ΔCO ratios by selecting data with TEBCcal > 80%. The annually averaged ΔBC/ΔCO ratios for air originated from north and south China were 7.0 ± 3.3 and 7.5 ± 4.6 ng m−3 ppbv−1, respectively, about half the annual BC/CO emission ratio derived from the emission inventory of Zhang et al. (2009). We evaluate the CO emission inventory of Zhang et al. (2009) for China by comparing observed (ground-based and aircraft) and model-calculated CO values. The comparison indicates that the CO emissions from China were underestimated by about a factor of 2.