Equivalent Black Carbon Research Articles

A Factor and Trends Analysis of Multidecadal Lower Tropospheric Observations of Arctic Aerosol Composition, Black Carbon, Ozone, and Mercury at Alert, Canada

AbstractObservations from 1980 to 2013 of 20 aerosol constituents, ozone and mercury at Alert, Canada (82.50°N, 62.35°W), were analyzed for trends and dominant factors of the Arctic haze during winter and spring. Trends reflect changing emissions in Eurasia, the main source region for surface pollution in the high Arctic. SO42−, H+, NH4+, K+, Cu, Ni, Pb, Zn, nonsoil V, nonsoil Mn, and equivalent black carbon decreased between 23% and 80% as emissions declined rapidly in northern Eurasia during the early 1990s. NO3− increased by 20% as aerosol acidity declined. Metals were linked to emissions from smelting and fossil fuel combustion. In winter, ozone increased by 5% over 23 years, consistent with other observations and global modeling. Twelve PMF factors emerged for the dark period (November to February) and 13 for the light period (March to May). Eleven PMF factors are common to both dark and light, a twelfth factor was associated with sulfate in the dark and nitrate in the light, and the thirteenth (light period) was related to ozone and gaseous mercury depletion near Alert. IODINE and NITRATE factors, important for Arctic chemistry, changed with sunlight. In the light, 50% of all NO3− was on the NITRATE factor, while in the dark, most was associated with MODIFIED SEA SALT and equivalent black carbon. In the dark (light), 90% (28%) of iodine were found on the factor IODINE and 58% associated with SEA‐SALT and MODIFIED SEA‐SALT. These results help in understanding the role of atmospheric chemistry in weather and climate processes.

Aerosol Characteristics in the Near-Ground Layer of the Atmosphere of the City of Tomsk in Different Types of Aerosol Weather

Considering the wide range of variability of all aerosol characteristics (especially in the near-ground layer of the atmosphere near industrial centers), when creating a realistic empirical model of optical and microphysical characteristics, the optimal dividing of the total data array according to some multifactor signs is needed. In this paper, we analyze the main states of “dry” aerosol on the basis of the results of long-term regular measurements in the near-ground layer of the atmosphere near the city of Tomsk in 2000–2017. The following parameters were considered: aerosol number concentration and size distribution function, total and angular scattering coefficients, including the small-angle range 1.2° to 20°, mass concentration and size distribution of absorbing substances (equivalent black carbon), characteristics of the aerosol hygroscopic properties, and spectral aerosol extinction of radiation on an open long path in the wavelength range 0.45 to 3.9 µm. In our comprehensive study, we first proposed and developed an original approach (classification) to study the optical and microphysical properties of atmospheric aerosol of various physicochemical origins (background, smoke, smog, anthropogenic, etc.) based on dividing the entire data array into characteristic subarrays (types of aerosol weather), which differ from each other in a different combination of scattering and absorbing properties of particles. To divide the total data array into types of aerosol weather including “Background”, “Haze-S”, “Smog”, and “Smoke haze”, the values of the scattering coefficient of the dry aerosol matter σd(λ = 0.51 μm) = 100 Mm−1 and the ratio of the mass concentration of the absorbing substance to the mass concentration of submicron aerosol P = 0.05. The results showed that most of the seasonal average values of the aerosol parameters analyzed in the paper are statistically significantly different when comparing various characteristic types of scattering and absorbing atmospheric aerosol. The results of the research indicate that the application of the developed classification of types of aerosol weather for the analyzed optical and microphysical parameters of aerosol particles is quite effective and reasonable.

Detection of tar brown carbon with a single particle soot photometer (SP2)

Abstract. We investigate the possibility that the refractory, infrared-light-absorbing carbon particulate material known as “tarballs” or tar brown carbon (tar brC) generates a unique signal in the scattering and incandescent detectors of a single particle soot photometer (SP2). As recent studies have defined tar brC in different ways, we begin by reviewing the literature and proposing a material-based definition of tar. We then show that tar brC results in unique SP2 signals due to a combination of complete or partial evaporation, with no or very little incandescence. Only a subset of tar brC particles exhibited detectable incandescence (70 % by number); for these particles the ratio of incandescence to light scattering was much lower than that of soot black carbon (BC). At the time of incandescence the ratio of light scattering to incandescence from these particles was up to 2-fold greater than from soot (BC). In our sample, where the mass of tar was 3-fold greater than the mass of soot, this led to a bias of <5 % in SP2-measured soot mass, which is negligible relative to calibration uncertainties. The enhanced light scattering of tar is interpreted as being caused by tar being more amorphous and less graphitic than soot BC. The fraction of the tar particle which does incandesce was likely formed by thermal annealing during laser heating. These results indicate that laser-induced incandescence, as implemented in the SP2, is the only BC measurement technique which can quantify soot BC concentrations separately from tar while also potentially providing real-time evidence for the presence of tar. In contrast, BC measurement techniques based on thermal–optical (EC: elemental carbon) and absorption (eBC: equivalent BC) measurements cannot provide such distinctions. The optical properties of our tar particles indicate a material similarity to the tar particles previously reported in the literature. However, more- and less-graphitized tar samples have also been reported, which may show stronger and weaker SP2 responses, respectively.

On-flight intercomparison of three miniature aerosol absorption sensors using unmanned aerial systems (UASs)

Abstract. The present study investigates and compares the ground and in-flight performance of three miniaturized aerosol absorption sensors integrated on board small-sized Unmanned Aerial Systems (UASs). These sensors were evaluated during two contrasted field campaigns performed at an urban site, impacted mainly by local traffic and domestic wood burning sources (Athens, Greece), and at a remote regional background site, impacted by long-range transported sources including dust (Cyprus Atmospheric Observatory, Agia Marina Xyliatou, Cyprus). The miniaturized sensors were first intercompared at the ground-level against two commercially available instruments used as a reference. The measured signal of the miniaturized sensors was converted into the absorption coefficient and equivalent black carbon concentration (eBC). When applicable, signal saturation corrections were applied, following the suggestions of the manufacturers. The aerosol absorption sensors exhibited similar behavior against the reference instruments during the two campaigns, despite the diversity of the aerosol origin, chemical composition, sources, and concentration levels. The deviation from the reference during both campaigns concerning (eBC) mass was less than 8 %, while for the absorption coefficient it was at least 15 %. This indicates that those sensors that report black carbon mass are tuned and corrected to measure eBC more accurately than the absorption coefficient. The overall potential use of miniature aerosol absorption sensors on board small UASs is also illustrated. UAS-based absorption measurements were used to investigate the vertical distribution of eBC over Athens up to 1 km above sea level during January 2016, exceeding the top of the planetary boundary layer (PBL). Our results reveal a heterogeneous boundary layer concentration of absorbing aerosol within the PBL intensified in the early morning hours due to the concurrent peak traffic emissions at ground-level and the fast development of the boundary layer. After the full development of the PBL, homogenous concentrations are observed from 100 m a.g.l. to the PBL top.

Analysis of equivalent black carbon multi-year data at an oil pre-treatment plant: Integration with satellite data to identify black carbon transboundary sources

This study analyzes a multi-year dataset of equivalent black carbon (EBC) concentration collected in 2012–2015 by a 7-wavelengths Aethalometer at Centro Olio Val d’Agri (COVA) in southern Italy, which is the largest European oil pre-treatment plant. These data, together with the local air circulation analysis, were used to identify the black carbon (BC) sources in Agri valley, specifically the COVA plant and vehicular traffic. During a limited period of 2012–2013, simultaneous measurements of PM10 concentration were available for comparison with the EBC data, which revealed correlation values of 0.31–0.43 between PM10 and EBC indicating a relevant contribution of BC to particulate matter at the site. On average, EBC/PM10 ratio is 7%, a value equal to that found at an urban-background site in Rome measured during non-rush hours.Moreover, an ad hoc procedure combining EBC data, Hybrid Single-Particle Lagrangian Integrated Trajectory back-trajectories (HYSPLIT), and satellite fire data enabled detection of days affected by the transport of carbonaceous particles. Both Visible Infrared Imaging Radiometer Suite (VIIRS) and Moderate Resolution Imaging Spectroradiometer (MODIS) satellite data were used as input for the algorithm, and the corresponding results were compared and discussed. VIIRS showed a better performance in detecting smaller/cooler hotspots especially in cases of flaring, as observed during flaring events at the COVA plant itself.Application of the procedure suggests that both regional and non-regional biomass burning episodes, which occur mainly during summer, could contribute to the BC load at the site.The approach applied to the case study of the present work can be useful for estimating the relative contributions of local and remote sources of BC.

Large Summer Contribution of Organic Biogenic Aerosols to Arctic Cloud Condensation Nuclei

AbstractA k‐means cluster analysis of a 5‐year aerosol particle size distribution data set from northeast Greenland is combined with measurements of coincident shorter field studies of aerosol equivalent black carbon (eBC) content, hygroscopic growth factor (HGF), and cloud condensation nuclei (CCN) concentrations. This led to five clusters strongly controlled by natural emissions (eBC 8–15 ng/m3) and three anthropogenic clusters with larger particle concentrations in the accumulation mode (eBC 29–77 ng/m3). The HGF and CCN properties of the eight aerosol clusters differ drastically. Anthropogenic clusters feature high growth factors (1.62–1.81) and low CCN κ values (0.10–0.46), while natural clusters show lower HGF (1.38–1.70) but remarkably higher κ values (0.35–0.51). Extrapolating the CCN properties on the basis of the cluster analysis to annual timescales suggests that biogenic organic aerosol may drive Arctic aerosol production during summer.

Aerosol Particle and Black Carbon Emission Factors of Vehicular Fleet in Manila, Philippines

Poor air quality has been identified as one of the main risks to human health, especially in developing regions, where the information on physical chemical properties of air pollutants is lacking. To bridge this gap, we conducted an intensive measurement campaign in Manila, Philippines to determine the emission factors (EFs) of particle number (PN) and equivalent black carbon (BC). The focus was on public utility jeepneys (PUJ), equipped with old technology diesel engines, widely used for public transportation. The EFs were determined by aerosol physical measurements, fleet information, and modeled dilution using the Operational Street Pollution Model (OSPM). The results show that average vehicle EFs of PN and BC in Manila is up to two orders of magnitude higher than European emission standards. Furthermore, a PUJ emits up to seven times more than a light-duty vehicles (LDVs) and contribute to more than 60% of BC emission in Manila. Unfortunately, traffic restrictions for heavy-duty vehicles do not apply to PUJs. The results presented in this work provide a framework to help support targeted traffic interventions to improve urban air quality not only in Manila, but also in other countries with a similar fleet composed of old-technology vehicles.

Analysis of Absorption Characteristics and Source Apportionment of Carbonaceous Aerosol in Arid Region of Western India

The present work analyses the equivalent Black Carbon (EBC) data obtained using Aethalometer (AE-33) located at India Meteorological Department, Jodhpur, Rajasthan during the year 2016. The annual mean EBC concentration is 5.76 µg m−3 and the monthly mean concentration is maximum (12.12 µg m−3) in January and minimum (1.27 µg m−3) in December. The seasonal mean of wind speeds are 1.94, 2.02, 1.34, 1.02 m s−1 and the calm percentages are 7, 5.7, 28.7, 25.7% during pre-monsoon (MAM), monsoon (JJAS), post-monsoon (ON) and winter (DJF), respectively. The night time EBC concentrations are more than the day time concentrations due to the shallowness of the boundary layer and local anthropogenic activities. The Concentrated Weighted Trajectories (CWT) are calculated using back trajectories ending at 100 m above ground level at Jodhpur station using National Centre for Medium Range Weather Forecast (NCMRWF) Global Forecast System (GFS) based reanalysis T574 data. The CWT, directional source region analysis reveals the effect of long-range transport in the winter season with a 60% of probability of source regions from the W, NW direction of observational site. Source apportionment also carried out by assuming alpha (at 470-, 950-nm wavelengths) close to 1 for anthropogenic emissions and alpha close to 2 for biomass burning aerosols. The monthly mean biomass burning concentration is found maximum (2.58 µg m−3) in November and minimum (0.22 µg m−3) in July.

Application of a high-temporal resolution model for the identification of columnar aerosol components

A high-temporal resolution model for the identification of columnar aerosol composition was applied to two sets of radiometric measurements obtained one in a semi-rural site of South Italy and the other in an urban/traffic site of the Po Valley, northern Italy. Inputs of the model are the spectral Aerosol Optical Depths (AODs) from direct solar radiation data to derive the contribution to the total extinction of nine aerosol species, i. e Water Soluble (WS), Black Carbon (BC), Sea Salt accumulation (SSacc), Sea Salt coarse (SScoa), Biogenic (Bio), Mineral Coarse (Mcoa), Mineral Accumulation (Macc), Small Organic Matter (SOM), and Large Organic Matter (LOM). In order to better parameterize the absorptive properties of dust and organic particles, a wavelength dependent imaginary part of the refractive index was used for dust and organics. Despite the differences between the two sites, a prevalence of fine aerosols (organics, WS and BC) was found in both cases suggesting the relevance of anthropogenic sources such as traffic. The retrieved AOD BC component was compared to Equivalent BC (EBC) concentrations measured in situ by an aethalometer at both sites. For mean daily values good correlations were found (R2 = 0.7), whereas high-temporal resolution (hourly basis) columnar composition was verified to be more reliable in cases of surface-column coupling. The possibility to apply this simple model to direct irradiance data from portable radiometers in areas where no routine measurements are available, and obtaining results with an increased temporal resolution, can help to gather information on aerosol columnar composition to be used in radiative, climate and transport models.

The characteristics and local-regional contributions of atmospheric black carbon over urban and suburban locations in Shanghai, China

Black carbon (BC), produced from the incomplete combustion of carbonaceous fuels, has emerged as a major contributor to global climate change with adverse health effects. Based on one-year (2016.06.01–2017.06.30) equivalent black carbon (eBC) measurements, this study analyzed the characteristics of eBC concentrations and the local-regional contributions at an urban site (Pudong, PD) and a suburban site (Qingpu, QP) in Shanghai, China. The results showed that the annual average eBC concentrations were 1.17 ± 0.61 μg m−3 and 2.09 ± 0.97 μg m−3 at PD and QP, respectively. The high eBC concentrations occurred in winter and at weekends both for PD and QP. There were significant negative correlation coefficients between the daily eBC, the daily wind speed (WS) and the daily boundary layer height (BLH) at PD (rws: 0.45, rblh = −0.35, p < 0.01) and QP (rws: 0.49, rblh = −0.32, p < 0.01). And the relative higher eBC concentrations coincided with southerly, southwesterly and westerly winds although these winds had lower frequencies. This could be related to the agricultural fire in these directions during summer harvesttime. The significant partial correlation coefficients of eBC-CO (ru:0.37–0.64, rs:0.18–0.44, p < 0.01) and eBC-NO2 (ru:0.49–0.74, rs:0.38–0.75, p < 0.01) could suggest that eBC mainly come from vehicular exhaust emissions in Shanghai. Besides, the higher eBC/PM2.5 (5.29% ± 1.94%) and eBC/CO(0.30% ± 0.14%) at QP indicated the more combustion activities and diesel-powered vehicle emissions in suburban areas. The concentration weighted trajectory (CWT) analysis indicated that the surrounding areas at the junction of Shanghai, Jiangsu, and Zhejiang provinces seemed to be relatively the most important sources outside of Shanghai.

Methodology for high-quality mobile measurement with focus on black carbon and particle mass concentrations

Abstract. Measurements of air pollutants such as black carbon (BC) and particle mass concentration in general, using mobile platforms equipped with high-time-resolution instruments, have gained popularity over the last decade due to their wide range of applicability. Assuring the quality of mobile measurement, data have become more essential, particularly when the personal exposure to pollutants is related to their spatial distribution. In the following, we suggest a methodology to achieve data from mobile measurements of equivalent black carbon (eBC) and PM2.5 mass concentrations with high data quality. Besides frequent routine quality assurance measures of the instruments, the methodology includes the following steps: (a) measures to ensure the quality of mobile instruments through repeated collocated measurements using identical instrumentation, (b) inclusion of a fixed station along the route containing quality-assured reference instruments, and (c) sufficiently long and frequent intercomparisons between the mobile and reference instruments to correct the particle number and mass size distributions obtained from mobile measurements. The application of the methodology can provide the following results. First, collocated mobile measurements with sets of identical instruments allow identification of undetected malfunctions of the instruments. Second, frequent intercomparisons against the reference instruments will ensure the quality of the mobile measurement data of the eBC mass concentration. Third, the intercomparison data between the mobile optical particle size spectrometer (OPSS) and a reference mobility particle size spectrometer (MPSS) allow for the adjustment of the OPSS particle number size distribution using physically meaningful corrections. Matching the OPSS and MPSS volume particle size distributions is crucial for the determination of PM2.5 mass concentration. Using size-resolved complex refractive indices and time-resolved fine-mode volume correction factors of the fine-particle range, the calculated PM2.5 from the OPSS was within 5 % of the reference instruments (MPSS+APSS). However, due to the nonsphericity and an unknown imaginary part of the complex refractive index of supermicrometer particles, a conversion to a volume equivalent diameter yields high uncertainties of the particle mass concentration greater than PM2.5. The proposed methodology addresses issues regarding the quality of mobile measurements, especially for health impact studies, validation of modeled spatial distribution, and development of air pollution mitigation strategies.

Inter-comparison of carbon content in PM10 and PM2.5 measured with two thermo-optical protocols on samples collected in a Mediterranean site.

Scientific interest is focusing on different approaches for characterising organic carbon (OC), elemental carbon (EC) and equivalent black carbon (eBC), although EUSAAR2 protocol has been established and frequently used in EU for regulatory purposes. Discrepancies are observed due to thermal protocols used for OC/EC determinations and the effect of the chemical-physical properties of aerosol using optical measurements for eBC. In this work, a long-term inter-comparison of carbon measurements with two widely used protocols (EUSAAR2 and NIOSH870) was performed on PM2.5 and PM10 samples. The influence of the protocol on the evaluation of secondary organic aerosol (SOC) and on the correlation between EC and eBC was investigated. An extensive check of repeatability gave typical uncertainties of ~ 5% for TC and OC, and ~ 10% for EC for both thermal protocols. Results show that OC is statistically comparable between the two protocols but EC is significantly higher with EUSAAR2, especially during the warm season. The ratio OC/EC is lower with EUSAAR2, also showing a seasonality (lower values in the warm season) not observed with NIOSH870. Despite the differences in OC/EC ratios, the contribution of SOC to OC (~ 50%), evaluated using the EC-tracer method, did not differ significantly between the two protocols and for both size fractions. Further, SOC/OC ratios were comparable in cold and warm periods. eBC/EC ratios larger than one for both protocols were obtained, 1.62 (EUSAAR2) and 1.92 (NIOSH870), and also correlated with the ratio OC/EC for both protocols, especially in the cold season.

Black carbon aerosols in the ambient air of Gangotri Glacier valley of north-western Himalaya in India

The warming effect of equivalent Black Carbon (EBC) aerosols due to their light absorbing nature is a serious environmental concern, particularly, in the eco-sensitive and glaciated Himalayan region. Moreover, baseline data on BC is rarely available from most of the glaciated Himalayan region. For the first time, measurements on ambient EBC mass concentration were made at a high altitude site Chirbasa (3600 m, amsl), near Gangotri Glacier in the Indian Himalaya, during the year 2016. The change in the EBC concentration over the year was recorded from 0.01 μg m−3 to 4.62 μg m−3 with a diurnal variability of 0.10 μg m−3 to 1.8 μg m−3. The monthly mean concentration of EBC was found to be minimum (0.089 ± 0.052 μg m−3) in August and maximum (0.840 ± 0.743 μg m−3) in the month of May. The observed seasonal mean concentrations of EBC are less than 0.566 μg m−3 whereas the annual mean is 0.395 ± 0.408 μgm−3 indicating a pristine glacial and absence of locality EBC sources. Further, investigation on the occasional high values extricated that the seasonal cycle of EBC was significantly influenced by the emissions resulting from agriculture burning (in western part of the country), forest fires (along the Himalayan slopes) in summer, and to some extent the contribution from long range transport of pollutants in winter, depending the prevailing meteorological condition.

Seasonal features and origins of carbonaceous aerosols at Syowa Station, coastal Antarctica

Abstract. We have measured black carbon (BC) concentrations at Syowa Station, Antarctica, since February 2005. The measured BC concentrations in 2005–2016 were corrected to equivalent BC (EBC) concentrations using Weingartner's method. Seasonal features of EBC concentrations, long-range transport from mid-latitudes to the Antarctic coast, and their origins were characterized. Results show that daily median EBC concentrations were below the detection limit (0.2 ng m−3) to 63.8 ng m−3 at Syowa Station (median, 1.8 ng m−3; mean, 2.7 ng m−3 during the measurement period of February 2005–December 2016). Although seasonal features and year-to-year variations in EBC concentrations were observed, no long-term trend of EBC concentrations was clear during our measurement period. Seasonal features of EBC concentrations showed a spring maximum during September–October at Syowa Station. To elucidate EBC transport processes, origins, and the potential source area (PSA), we compared EBC data to backward trajectory analysis and chemical transport model simulation. From comparison with backward trajectory, high EBC concentrations were found in air masses from the marine boundary layer. This finding implies that transport via the marine boundary layer was the most important transport pathway to EBC concentrations at Antarctic coasts. Some EBC was supplied to the Antarctic region by transport via the upper free troposphere. Chemical transport model simulation demonstrated that the most important origins and PSA of EBC at Syowa Station were biomass burning in South America and southern Africa. Fossil fuel combustion in South America and southern Africa also have important contributions. The absorption Ångström exponent (AAE) showed clear seasonal features with 0.5–1.0 during April–October and maximum (1.0–1.5) in December–February. The AAE features might be associated with organic aerosols and mixing states of EBC.

Relationship between long-range transported atmospheric black carbon and carbon monoxide at a high-altitude background station in East Asia

Lulin Atmospheric Background Station (LABS, 23.47°N, 120.87°E; 2862 m above sea level) at the summit of Mount Lulin in central Taiwan was established in spring 2006 and is the only high-altitude background station over western Pacific region in East Asia to study the impact of various air pollutants through long-range transport. Continuous in-situ measurements of equivalent black carbon (EBC) and carbon monoxide (CO) concentrations were made at LABS from June 2012 to May 2014 and their association was investigated in this study. The highest monthly concentration of EBC (median; 840 ng m−3) and CO (212 ppbv) in March were primarily attributed to the westerly winds coupled with biomass-burning (BB) emissions from Southeast Asia (SEA) region. The association of EBC and CO was weak at LABS possibly due to the influence of dissimilar air masses from various sources, and scavenging or dilution of EBC during the long-range atmospheric transport to Mt. Lulin. The mean ΔEBC/ΔCO ratio (slope of least-squares regression line of ΔEBC-ΔCO scatterplot; where Δ indicates surplus amounts with respect to the background value) was found the most significant in March (5.3 ng m−3 ppbv−1 or 7.3 × 10−3 g of carbon as EBC per gram of carbon as CO). On the basis of episodic cases, the mean ΔEBC/ΔCO ratios at LABS were estimated to be 6.1, 8.0, and 2.4 ng m−3 ppbv−1 for SEA BB emissions, southern China mixed pollution, and northern China mixed pollution, respectively. A total of 32% loss in EBC aerosols (6.4% of EBC removal per day) was estimated for the atmospheric transport of BB emissions from SEA region to LABS. This study provides needful information to understand the ΔEBC/ΔCO ratios at a remote site and would be used in model simulations to evaluate BC aging and scavenging over western Pacific region in East Asia.

Intra-regional transport of black carbon between the south edge of the North China Plain and central China during winter haze episodes

Abstract. Black carbon (BC), which is formed from the incomplete combustion of fuel sources (mainly fossil fuel, biofuel and open biomass burning), is a chemically inert optical absorber in the atmosphere. It has significant impacts on global climate, regional air quality and human health. During transportation, its physical and chemical characteristics as well as its sources change dramatically. To investigate the properties of BC (i.e., mass concentration, sources and optical properties) during intra-regional transport between the southern edge of the North China Plain (SE-NCP) and central China (CC), simultaneous BC observations were conducted in a megacity (Wuhan – WH) in CC, in three borderline cities (Xiangyang – XY, Suixian – SX and Hong'an – HA; from west to east) between the SE-NCP and CC, and in a city (Luohe – LH) in the SE-NCP during typical winter haze episodes. Using an Aethalometer, the highest equivalent BC (eBC) mass concentrations and the highest aerosol absorption coefficients (σabs) were found in LH in the SE-NCP, followed by the borderline cities (XY, SX and HA) and WH. The levels, sources, optical properties (i.e., σabs and absorption Ångström exponent, AAE) and geographic origins of eBC were different between clean and polluted periods. Compared with clean days, higher eBC levels (26.4 %–163 % higher) and σabs (18.2 %–236 % higher) were found during pollution episodes due to the increased combustion of fossil fuels (increased by 51.1 %–277 %), which was supported by the decreased AAE values (decreased by 7.40 %–12.7 %). The conditional bivariate probability function (CBPF) and concentration-weighted trajectory (CWT) results showed that the geographic origins of biomass burning (BCbb) and fossil fuel (BCff) combustion-derived BC were different. Air parcels from the south dominated for border sites during clean days, with contributions of 46.0 %–58.2 %, whereas trajectories from the northeast showed higher contributions (37.5 %–51.2 %) during pollution episodes. At the SE-NCP site (LH), transboundary influences from the south (CC) exhibited a more frequent impact (with air parcels from this direction comprising 47.8 % of all parcels) on the ambient eBC levels during pollution episodes. At WH, eBC was mainly from the northeast transport route throughout the observation period. Two transportation cases showed that the mass concentrations of eBC, BCff and σabs all increased, from upwind to downwind, whereas AAE decreased. This study highlights that intra-regional prevention and control for dominant sources at each specific site should be considered in order to improve the regional air quality.

Fireworks: A major source of inorganic and organic aerosols during Christmas and New Year in Mexico city

Abstract The fireworks activity in Christmas and New Year is the culprit of a substantial increase in the particles pollution during those festivity dates in Mexico City. The fireworks' thrilling explosions fill the air with small particles full of metals and organic and inorganic species, and noxious gases such as sulfur dioxide, nitrogen dioxide, carbon monoxide and nitrous acid (HONO). The stagnant atmosphere at night accumulates the fireworks haze under a shallow boundary layer. By sunrise, once the fireworks activity has stopped, the photolysis of the abundant HONO accumulated throughout the night, leads to a rapid production of nitrate (NO3−), ammonium (NH4+), sulfate (SO42−) and low volatility secondary organic aerosols. This was the pattern observed during the winter of 2013–2014, when online measurements of water-soluble inorganic ions in particles smaller than 2.5 μm (PM2.5), non-refractory ions and organics in particles smaller than 1 μm (PM1), equivalent black carbon, and above-mentioned gases were conducted. The geometric average of the sum of the three major inorganic ions, NO3−, NH4+ and SO42− accounted for 25% (28%) and 34% (37%) of the total PM2.5 mass during the fireworks activity at night and the following morning on Christmas Day (New Year's Day), respectively. Similarly, their sum in the non-refractory fraction accounted for 37% (49%) and 47% (53%) of the total NR-PM1 mass concentration, while the organic fraction accounted for 56% (44%) and 49% (44%). Biomass burning organic aerosols and semi-volatile oxygenated organic aerosols (BBOA and SV-OOA, respectively) dominated the organic fraction during the fireworks period at night, while the low-volatility oxygenated organic aerosols (LV-OOA) increased substantially their concentration along the post-firework hours the following morning. Concentrations of PM2.5 > 100 μg m−3 and PM1 > 50 μg m−3 were observed on both days, with maximums of 157 and 137 μg m−3 for PM2.5 and PM1, respectively. The meteorological conditions helped to reduce the fireworks impact by late afternoon on both days, limiting the firework episodes to 22 h. The SO42− and NO3− related to the fireworks were not able to offset the deficit of NH4+, and thus the acidity nature of the particles during the mild winter of Mexico City did not change.

Personal exposure to air pollutants in a Bus Rapid Transit System: Impact of fleet age and emission standard

This work documents the extremely high concentrations of fine aerosol particles (PM2.5), equivalent black carbon (eBC) and carbon monoxide (CO) experienced by commuters in one of the world largest Bus Rapid Transit (BRT) systems, located in Bogotá, Colombia. A strong relationship between vehicle emissions standard and in-vehicle concentrations was established. Extensive measurements of PM2.5, eBC, and CO were carried out inside the system buses and stations. Measurements were performed during eleven months covering all the system lanes and a significant fraction of the bus fleet and stations. Based on the observed in-bus and in-station concentrations, travel times, and urban ambient levels, the contribution of a typical round trip in the BRT system to the daily inhaled dose was estimated to be 60% for PM2.5, and between 79% and 90% for eBC. The mean PM2.5 dose inhaled by commuters in a typical round trip in the system is 1.2 times the dose a subject would inhale over 24 h exposed to WHO guideline of 25 μgm−3. In 52 out of 180 buses sampled the mean in-cabin concentration of eBC was in excess of 100 μgm−3. Measurements show that mean ratio of in-bus to urban ambient concentration is 8:1 for PM2.5 and 4:1 for CO. These ratios were observed to be much larger when traveling inside the older fraction of the BRT fleet, reaching 11:1 and 7:1 for PM2.5 and CO respectively. These older buses consist exclusively of Euro II and Euro III nominal emission standard vehicles. Average exposure levels inside Euro II and III buses was twice as large as those measured inside vehicles with stricter emission standards, Euro IV or superior. Overall, the measurements suggest that the entrainment of polluted pockets of air to the semi enclosed micro-environments in the system, namely, buses and stations, explains the extreme observed exposure concentrations. Measurements inside an underground bus-station where traffic is restricted to only BRT buses, and on-board a zero emission fully electric BRT bus suggested most of the pollution in the system comes from entrainment of the exhaust of the diesel-powered BRT buses. The significantly lower exposure and inhaled dose of PM2.5, eBC, and CO observed for commuters in newer vehicles suggests that a fleet renewal could have a disproportionately large impact on reducing population exposure to air pollutants. The extent of the reduction in exposure and inhaled dose through fleet renewal is proportional to the gradient of in-bus to urban ambient air pollution levels.

Vertical characterization of aerosol optical properties and brown carbon in winter in urban Beijing, China

Abstract. Aerosol particles are of importance in the Earth's radiation budget since they scatter and absorb sunlight. While extensive studies of aerosol optical properties have been conducted at ground sites, vertical measurements and characterization are very limited in megacities. In this work, we present simultaneous real-time online measurements of aerosol optical properties at ground level and at 260 m on a meteorological tower from 16 November to 13 December in 2016 in Beijing along with measurements of continuous vertical profiles during two haze episodes. The average (±1σ) scattering and absorption coefficients (bsca and babs; λ=630 nm) were 337.6 (±356.0) and 36.6 (±33.9) Mm−1 at 260 m, which were 26.5 % and 22.5 % lower than those at ground level. Single scattering albedo (SSA), however, was comparable between the two heights, with slightly higher values at ground level (0.89±0.04). Although bsca and babs showed overall similar temporal variations between ground level and 260 m, the ratios of 260 m to ground varied substantially from less than 0.4 during the clean stages of haze episodes to &gt; 0.8 in the late afternoon. A more detailed analysis indicates that vertical profiles of bsca, babs, and SSA in the low atmosphere were closely related to the changes in meteorological conditions and mixing layer height. The mass absorption cross section (MAC) of equivalent black carbon (eBC, λ=630 nm) varied substantially from 9.5 to 13.2 m2 g−1 in winter in Beijing, and it was strongly associated with the mass ratio of coating materials on refractory BC (rBC) to rBC (MR), and also the oxidation degree of organics in rBC-containing particles. Our results show that the increases in MAC of eBC in winter were mainly caused by photochemically produced secondary materials. Light absorption of organic carbon (brown carbon, BrC) was also important in winter, which on average accounted for 46 (±8.5) % and 48 (±9.3) % of the total absorption at 370 nm at ground level and 260 m, respectively. A linear regression model combined with positive matrix factorization analysis was used to show that coal combustion was the dominant source contribution of BrC (48 %–55 %) followed by biomass burning (17 %) and photochemically processed secondary organic aerosol (∼20 %) in winter in Beijing.

Sources of atmospheric black carbon and related carbonaceous components at Rishiri Island, Japan: The roles of Siberian wildfires and of crop residue burning in China

A field study was conducted to clarify sources of atmospheric black carbon and related carbonaceous components at Rishiri Island, Japan. We quantified equivalent black carbon (eBC) particle mass and the absorption Ångström exponent (AAE), atmospheric CO and CH4, in addition to levoglucosan in total suspended particles, a typical tracer of biomass burning. Sixteen high eBC events were identified attributable to either anthropogenic sources or biomass burning in Siberia/China. These events were often accompanied by increases of co-emitted gases such as CH4 and CO. Specifically, we observed pollution events with elevated eBC, AAE, levoglucosan, and CH4CO slope in late July 2014, which were attributed to forest fires in Siberia by reference to the FLEXPART model footprint and fire hotspots. In autumn, drastic increases of eBC, AAE, and levoglucosan were observed, accompanied by an eBC–CO slope of >15 ng m−3/ppb, resulting from long-range transport of emissions from extensive burning of crop residue on the Northeast China Plain. Other than the sources of fossil fuel combustion in China and forest fires in Siberia, we report for the first time that pollution events in northern Japan are caused by crop residue burning in China. This study elucidated valuable information that will improve understanding of the effects of biomass burning in East Asia on atmospheric carbonaceous components.