Black Carbon Components Research Articles

Short-term effects of wildfire-specific fine particulate matter and its carbonaceous components on perinatal outcomes: A multicentre cohort study in New South Wales, Australia

BackgroundEpidemiological evidence on the association between wildfire-specific fine particulate matter (PM2.5) and its carbonaceous components with perinatal outcomes is limited.We aimed to examine the short-term effects of wildfire-specific PM2.5 and its carbonaceous components on perinatal outcomes. MethodsA multicentre cohort of 9743 singleton births during the wildfire seasons from 1 September 2009 to 31 December 2015 across six cities in New South Wales, Australia were linked with daily wildfire-specific PM2.5 and carbonaceous components (organic carbon and black carbon). Adjusted distributed lag Cox regression models with spatial clustering were performed to estimate daily and cumulative adjusted hazard ratios (aHRs) during the last four gestational weeks for preterm birth, stillbirth, nonvertex presentation, low 5-min Apgar score, special care nursery/neonatal intensive care unit (SCN/NICU) admission, and caesarean section. ResultsDaily aHRs per 10 µg/m3 PM2.5 showed nearly inverted ‘U’-shaped positive associations and daily cumulative aHRs that increased with increasing duration of the exposures. The aHRs for lag 0–6 days were 1.17 (95 % CI: 1.04, 1.32) for preterm birth, 1.40 (95 % CI: 1.11, 1.78) for stillbirth, 1.20 (95 % CI: 1.08, 1.33) for nonvertex presentation, 1.12 (95 % CI: 0.93, 1.35) for low 5-min Apgar score, 0.99 (95 % CI: 0.83, 1.19) for SNC/NICU admission, and 1.01 (95 % CI: 0.94, 1.08) for caesarean section. Organic carbon and black carbon components for lag 0–6 days showed positive associations. The highest component-specific aHRs were 1.09 (95 % CI: 1.03, 1.15) and 4.57 (95 % CI: 1.96, 10.68) for stillbirth per 1 µg/m3 organic carbon and black carbon, respectively. The subgroups identified as most vulnerable were female births, births to mothers with low socioeconomic status, and births to mothers with high biothermal exposure. ConclusionsPositive associations of short-term wildfire-specific PM2.5 exposure and its carbonaceous components with adverse perinatal outcomes suggest that policies to reduce exposure would benefit public health.

Long-term mortality burden trends attributed to black carbon and PM2·5 from wildfire emissions across the continental USA from 2000 to 2020: a deep learning modelling study

Long-term improvements in air quality and public health in the continental USA were disrupted over the past decade by increased fire emissions that potentially offset the decrease in anthropogenic emissions. This study aims to estimate trends in black carbon and PM2·5 concentrations and their attributable mortality burden across the USA. In this study, we derived daily concentrations of PM2·5 and its highly toxic black carbon component at a 1-km resolution in the USA from 2000 to 2020 via deep learning that integrated big data from satellites, models, and surface observations. We estimated the annual PM2·5-attributable and black carbon-attributable mortality burden at each 1-km2 grid using concentration-response functions collected from a national cohort study and a meta-analysis study, respectively. We investigated the spatiotemporal linear-regressed trends in PM2·5 and black carbon pollution and their associated premature deaths from 2000 to 2020, and the impact of wildfires on air quality and public health. Our results showed that PM2·5 and black carbon estimates are reliable, with sample-based cross-validated coefficients of determination of 0·82 and 0·80, respectively, for daily estimates (0·97 and 0·95 for monthly estimates). Both PM2·5 and black carbon in the USA showed significantly decreasing trends overall during 2000 to 2020 (22% decrease for PM2·5 and 11% decrease for black carbon), leading to a reduction of around 4200 premature deaths per year (95% CI 2960-5050). However, since 2010, the decreasing trends of fine particles and premature deaths have reversed to increase in the western USA (55% increase in PM2·5, 86% increase in black carbon, and increase of 670 premature deaths [460-810]), while remaining mostly unchanged in the eastern USA. The western USA showed large interannual fluctuations that were attributable to the increasing incidence of wildfires. Furthermore, the black carbon-to-PM2·5 mass ratio increased annually by 2·4% across the USA, mainly due to increasing wildfire emissions in the western USA and more rapid reductions of other components in the eastern USA, suggesting a potential increase in the relative toxicity of PM2·5. 100% of populated areas in the USA have experienced at least one day of PM2·5 pollution exceeding the daily air quality guideline level of 15 μg/m3 during 2000-2020, with 99% experiencing at least 7 days and 85% experiencing at least 30 days. The recent widespread wildfires have greatly increased the daily exposure risks in the western USA, and have also impacted the midwestern USA due to the long-range transport of smoke. Wildfires have become increasingly intensive and frequent in the western USA, resulting in a significant increase in smoke-related emissions in populated areas. This increase is likely to have contributed to a decline in air quality and an increase in attributable mortality. Reducing fire risk via effective policies besides mitigation of climate warming, such as wildfire prevention and management, forest restoration, and new revenue generation, could substantially improve air quality and public health in the coming decades. National Aeronautics and Space Administration (NASA) Applied Science programme, NASA MODIS maintenance programme, NASA MAIA satellite mission programme, NASA GMAO core fund, National Oceanic and Atmospheric Administration (NOAA) GEO-XO project, NOAA Atmospheric Chemistry, Carbon Cycle, and Climate (AC4) programme, and NOAA Educational Partnership Program with Minority Serving Institutions.

Effects of COVID‐19 lockdown measures on nitrogen dioxide and black carbon concentrations close to a major Italian motorway

AbstractDuring the first half of 2020, the Italian government imposed several restrictions to limit the spread of the COVID‐19 pandemic: at the beginning of March, a heavy lockdown regime was introduced leading to a drastic reduction of traffic and, consequently, traffic‐related emissions. The aim of this study is to evaluate the effects of these restrictions on pollutant concentrations close to a stretch of the Italian A22 motorway lying in the Alpine Adige valley. In particular, the analysis focuses on measured concentrations of nitrogen dioxide (NO2) and black carbon (BC). Results show that, close to the motorway, NO2 concentrations dropped by around 45% during the lockdown period with respect to the same time period of the previous 3 years. The equivalent analysis for BC shows that the component related to biomass burning, mostly due to domestic heating, was not particularly affected by the restrictions, while the BC component related to fossil fuels, directly connected to traffic, plummeted by almost 60% with respect to the previous years. Since atmospheric concentrations of pollutants depend both on emissions and meteorological conditions, which can mask the variations in the emission regime, a random forest algorithm is also applied to the measured concentrations, in order to better evaluate the effects of the restrictions on emissions. This procedure allows for obtaining business‐as‐usual and meteorologically normalized time series of both NO2 and BC concentrations. The results derived from the random forest algorithm clearly confirm the drop in NO2 emissions at the beginning of the lockdown period, followed by a slow and partial recovery in the following months. They also confirm that, during the lockdown, emissions of the BC component due to biomass burning were not significantly affected, while those of the BC component related to fossil fuels underwent an abrupt drop.

Evolution characteristic of atmospheric black carbon particles at a coastal site in the Pearl River Delta, China

The mixing of black carbon (BC) with secondary materials is a major uncertainty source in assessing its radiative forcing. However, current understanding of the formation and evolution of various BC components is limited, particularly in the Pearl River Delta, China. This study measured submicron BC-associated nonrefractory materials and the total submicron nonrefractory materials using a soot particle aerosol mass spectrometer and a high-resolution time-of-flight aerosol mass spectrometer, respectively, at a coastal site in Shenzhen, China. Two distinct atmospheric conditions were also identified to further explore the distinctive evolution of BC-associated components: polluted period (PP) and clean period (CP). Comparing the components of two particles, we found that more-oxidized organic factor (MO-OOA) prefers to form on BC during PP rather CP. The formation of MO-OOA on BC (MO-OOABC) was affected by both enhanced photochemical processes and nocturnal heterogeneous processes. Enhanced photo-reactivity of BC, photochemistry during the daytime, and heterogeneous reaction at nighttime were potential pathways for MO-OOABC formation during PP. The fresh BC surface was favorable for the formation of MO-OOABC. Our study shows the evolution of BC-associated components under different atmospheric conditions, which should be considered in regional climate models to improve the assessment of the climate effects of BC.

Source apportionment of black carbon and combustion-related CO2 for the determination of source-specific emission factors

Abstract. Black carbon (BC) aerosol typically has two major sources in the urban environment: traffic and domestic biomass burning, which has a significant contribution to urban air pollution during the heating season. Traffic emissions have been widely studied by both laboratory experiments (individual vehicle emission) and real-world measurement campaigns (fleet emission). However, emission information from biomass burning is limited, especially an insufficiency of experimental results from real-world studies. In this work, the black carbon burden in the urban atmosphere was apportioned to fossil fuel (FF) and biomass burning (BB) related components using the Aethalometer source apportionment model. Applying the BC source apportionment information, the combustion-related CO2 was apportioned by multilinear regression analysis, supposing that both CO2 components should be correlated with their corresponding BC component. The combination of the Aethalometer model with the multilinear regression analysis (AM-MLR) provided the source-specific emission ratios (ERs) as the slopes of the corresponding BC–CO2 regressions. Based on the ER values, the source-specific emission factors (EFs) were determined using the carbon content of the corresponding fuel. The analysis was carried out on a 3-month-long BC and CO2 dataset collected at three monitoring locations in Ljubljana, Slovenia, between December 2019 and March 2020. The measured mean site-specific concentration values were in the 3560–4830 ng m−3 and 458–472 ppm ranges for BC and CO2, respectively. The determined average EFs for BC were 0.39 and 0.16 g(kg fuel)−1 for traffic and biomass burning, respectively. It was also concluded that the traffic-related BC component dominates the black carbon concentration (55 %–64 % depending on the location), while heating has the major share in the combustion-related CO2 (53 %–62 % depending on the location). The method gave essential information on the source-specific emission factors of BC and CO2, enabling better characterization of urban anthropogenic emissions and the respective measures that may change the anthropogenic emission fingerprint.

Mixing state of black carbon at different atmospheres in north and southwest China

Abstract. Large uncertainties remain when estimating the radiative forcing by black carbon (BC) because the corresponding microphysical properties have not been well addressed. In this study, the BC size distributions were studied based on three different field campaigns at an urban site, a suburban site, and a background site in China using a single particle soot photometer (SP2) in tandem with a differential mobility diameter. Measurement results indicate that the BC particles were composed of either thinly or thickly coated aerosols. The mean number fractions of the thinly coated BC aerosols were 51 %, 67 %, and 21 % for the urban, suburban, and background sites, respectively. The corresponding thickly coated (thinly coated) core mass median diameters were 187 (154), 182 (146), and 238 (163) nm, respectively. The mean diameter of the thickly coated BC-containing aerosols was larger than that of the thinly coated BC-containing aerosols, while the mean BC core diameter of the thickly coated BC-containing aerosols was smaller than that of the thinly coated BC-containing aerosols. About 10 % of the BC-containing aerosols with the BC core are attached to the other non-BC components, which were mainly generated by coagulation between the BC and non-BC components. The measurement results in our study can be further used in modeling studies to help with constraining the uncertainties of the BC radiative effects.

Black Carbon Contributes Substantially to Allochthonous Carbon Storage in Deltaic Vegetated Coastal Habitats

Vegetated coastal habitats (VCHs) rank among the most intense carbon sinks in natural ecosystems, playing an important role in the global carbon cycle. A significant part of the organic carbon (OC) they store may be allochthonous OC that has been sequestered elsewhere. Yet, the compositions of allochthonous OC are largely unknown. Here, we present concentrations and carbon isotopic (13C and 14C) compositions and accumulation rates of carbon in the VCHs from major temperate-subtropical deltas of China: Yellow, Yangtze, and Pearl river deltas. We find that black carbon (BC) amounts to 9-25% of OC across sites. Temperate VCHs exhibit lower BC contents but higher BC contributions than subtropical VCHs. This seemingly counterintuitive result can be explained by increased accumulation of long-term, stable, allochthonous OC in temperate VCHs. BC in temperate VCHs contains 1.5-2 times more fossil BC than that in subtropical VCHs in the 1 m depth soil, which is likely influenced by atmospheric input and the aging effect. We estimate an accumulation rate of BC in China's VCHs of 33.1 ± 14.5 g m-2 year-1, acting as a hotspot for BC burial. These results point to a substantial and hitherto unquantified contribution of BC components to blue carbon storage, as well as the VCHs to global BC storage. Preservation of this old-aged, stable OC implies an important ecosystem service of the VCHs for climate change mitigation.

Combined analyses of hygroscopic properties of organic and inorganic components of three representative black carbon samples recovered from pyrolysis

Hygroscopicity of black carbon (BC) aerosols is a key factor determining their climate forcing effect and atmospheric lifetime. However, the compositional dependence of BC hygroscopicity is not well understood. Here, a variety of different compositional components were separated from three representative BC samples recovered from pyrolysis (grass and wheat straw derived BC, household soot), including water extracted fraction of BC (WEBC, 9–21 wt%), residue fraction of BC after water extraction (R-WEBC, 79–91 wt%), water extracted minerals (WEM, 9–18 wt%), alkali extracted organic carbon (OCAE, 1–9 wt%), and elemental carbon (EC, 37–48 wt%). The bulk BC and separated BC components were analyzed in detail by elemental analysis and combined spectroscopic analyses. Their equilibrium hygroscopicity was measured by gravimetric method over a range of relative humidity (RH) levels (10–94%). Compared with the two organic components (OCAE and EC), the inorganic component (WEM) exhibited much stronger water uptake at all RH levels. At 94% RH level, WEM accounted for 16–139% of the overall water uptake by BC, whereas OCAE and EC accounted for only 1–3% and 6–26%, respectively. The XRD analysis of WEBC and WEM from household soot at varying RH levels indicated that the enhanced water uptake by these two components as well as that by bulk BC at high RH levels was due to the deliquescent salts (e.g., KCl, NH4Cl, KNO3, and NaCl). The strong hysteresis loops observed for bulk BC and WEBC could be attributed to the organic-facilitated drastic structural and morphological rearrangement of mineral particles as evidenced by the optical microscope analysis. The diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) analysis reaffirmed the dominant role played by the inorganic component in the hygroscopic behaviors of BC.

Temporal Variability of Equivalent Black Carbon Components in Atmospheric Air in Southern Poland

This study assesses the air quality in Zabrze (southern Poland) based on the ambient concentrations of equivalent black carbon (eBC). eBC measurement campaigns were carried out from April 2019 to March 2020 using a modern AE33 Aethalometer, accompanied by parallel measurements of gaseous pollutants, PM10 and meteorological parameters. The use of the two-component AE33 model allows for the determination of the eBC from fossil fuel combustion (eBCff) and biomass burning (eBCbb). The obtained results showed a clear seasonal variability of eBC concentrations, with higher average levels in the heating season (4.70 µg·m−3) compared to the non-heating one (1.79 µg·m−3). In both seasons, the eBCff component had a dominant share in total eBC, which indicates significant emissions from the combustion of fossil fuels for heating purposes and from local traffic sources. The obtained results showed high correlation coefficients with gaseous and particulate pollutants, with the strongest relationship for eBC and carbon monoxide (CO). During the non-heating and heating period, both anticyclone and cyclone systems played an important role in shaping eBC, eBCff and eBCbb concentrations. High concentrations of all components occurred with a significant decrease in air temperature and solar radiation in winter.

A 150-year record of black carbon (soot and char) and polycyclic aromatic compounds deposition in Lake Phayao, north Thailand.

An improved understanding of the historical variation in the emissions and sources (biomass burning, BB vs. fossil fuel, FF combustion) of soot and char, the two components of black carbon (BC), and polycyclic aromatic compounds (PACs) may help in assessing the environmental effects of the Atmospheric Brown Cloud (ABC) in SE Asia. We therefore determined historical variations of the fluxes of soot, char, and PACs (24 polycyclic aromatic hydrocarbons (PAHs), 12 oxygenated PAHs (OPAHs), and 4 azaarenes) in a dated sediment core (covering the past ∼150 years) of Phayao Lake in Thailand. The soot fluxes have been increasing in recent times, but at a far lower rate than previously estimated based on BC emission inventories. This may be associated with a decreasing BB contribution as indicated by the decreasing char fluxes from old to young sediments. The fluxes of high- and low-molecular-weight (HMW and LMW) PAHs, OPAHs, and azaarenes all sharply increased after ∼1980, while the ΣLMW-/ΣHMW-PAHs ratios decreased, further supporting the reduction in BB contribution at the expense of increasing FF combustion emissions. We also suggest that the separate record of char and soot, which has up to now not been done in aerosol studies, is useful to assess the environmental effects of ABC because of the different light-absorbing properties of these two BC components. Our results suggest that besides the establishment of improved FF combustion technology, BB must be further reduced in the SE Asian region in order to weaken the ABC haze.

Integrating in situ Measurements and City Scale Modelling to Assess the COVID–19 Lockdown Effects on Emissions and Air Quality in Athens, Greece

The lockdown measures implemented worldwide to slow the spread of the COVID–19 pandemic have allowed for a unique real-world experiment, regarding the impacts of drastic emission cutbacks on urban air quality. In this study we assess the effects of a 7-week (23 March–10 May 2020) lockdown in the Greater Area of Athens, coupling in situ observations with estimations from a meteorology-atmospheric chemistry model. Measurements in central Athens during the lockdown were compared with levels during the pre- and post-lockdown 3-week periods and with respective levels in the four previous years. We examined regulatory pollutants as well as CO2, black carbon (BC) and source-specific BC components. Models were run for pre-lockdown and lockdown periods, under baseline and reduced-emissions scenarios. The in-situ results indicate mean concentration reductions of 30–35% for traffic-related pollutants in Athens (NO2, CO, BC from fossil fuel combustion), compared to the pre-lockdown period. A large reduction (53%) was observed also for the urban CO2 enhancement while the reduction for PM2.5 was subtler (18%). Significant reductions were also observed when comparing the 2020 lockdown period with past years. However, levels rebounded immediately following the lift of the general lockdown. The decrease in measured NO2 concentrations was reproduced by the implementation of the city scale model, under a realistic reduced-emissions scenario for the lockdown period, anchored at a 46% decline of road transport activity. The model permitted the assessment of air quality improvements on a spatial scale, indicating that NO2 mean concentration reductions in areas of the Athens basin reached up to 50%. The findings suggest a potential for local traffic management strategies to reduce ambient exposure and to minimize exceedances of air quality standards for primary pollutants.

Formation mechanism of soil PAH distribution: High and low urbanization

Urbanization is an important driving force for the distribution of polycyclic aromatic hydrocarbons (PAHs) in urban soils. Research on factors affecting PAH distribution in urban soils has focused on analyses of statistical relationships, and quantitative models are not available in the literature. Accordingly, we chose the urban area of Nanjing (high urbanization), and Dingshu (low urbanization), and then comprehensively utilized soil sample test analyses, multivariate statistics, and other technical means to (1) study the concentration and sources of PAHs in urban soils, and (2) identify the main controlling factors that affect urban soil PAH distribution. We found that the population density and black carbon (BC) components were the critical factors of soil PAH distribution in Nanjing, yet BC components and leaf area index in Dingshu. We then constructed a quantitative relationship model of urban soil PAH distribution in different levels of urbanization. Using this model, we conducted a preliminary analysis of the formation mechanism of urban soil PAHs under different urbanization levels. This research provides a basis for finely controlling regional urban soil PAH pollution.

Radiative absorption enhancements by black carbon controlled by particle-to-particle heterogeneity in composition

Black carbon (BC) absorbs solar radiation, leading to a strong but uncertain warming effect on climate. A key challenge in modeling and quantifying BC's radiative effect on climate is predicting enhancements in light absorption that result from internal mixing between BC and other aerosol components. Modeling and laboratory studies show that BC, when mixed with other aerosol components, absorbs more strongly than pure, uncoated BC; however, some ambient observations suggest more variable and weaker absorption enhancement. We show that the lower-than-expected enhancements in ambient measurements result from a combination of two factors. First, the often used spherical, concentric core-shell approximation generally overestimates the absorption by BC. Second, and more importantly, inadequate consideration of heterogeneity in particle-to-particle composition engenders substantial overestimation in absorption by the total particle population, with greater heterogeneity associated with larger model-measurement differences. We show that accounting for these two effects-variability in per-particle composition and deviations from the core-shell approximation-reconciles absorption enhancement predictions with laboratory and field observations and resolves the apparent discrepancy. Furthermore, our consistent model framework provides a path forward for improving predictions of BC's radiative effect on climate.

Six-year source apportionment of submicron organic aerosols from near-continuous highly time-resolved measurements at SIRTA (Paris area, France)

Abstract. Organic aerosol (OA) particles are recognized as key factors influencing air quality and climate change. However, highly time-resolved long-term characterizations of their composition and sources in ambient air are still very limited due to challenging continuous observations. Here, we present an analysis of long-term variability of submicron OA using the combination of an aerosol chemical speciation monitor (ACSM) and a multiwavelength Aethalometer from November 2011 to March 2018 at a peri-urban background site of the Paris region (France). Source apportionment of OA was achieved via partially constrained positive matrix factorization (PMF) using the multilinear engine (ME-2). Two primary OA (POA) and two oxygenated OA (OOA) factors were identified and quantified over the entire studied period. POA factors were designated as hydrocarbon-like OA (HOA) and biomass burning OA (BBOA). The latter factor presented a significant seasonality with higher concentrations in winter with significant monthly contributions to OA (18 %–33 %) due to enhanced residential wood burning emissions. HOA mainly originated from traffic emissions but was also influenced by biomass burning in cold periods. OOA factors were distinguished between their less- and more-oxidized fractions (LO-OOA and MO-OOA, respectively). These factors presented distinct seasonal patterns, associated with different atmospheric formation pathways. A pronounced increase in LO-OOA concentrations and contributions (50 %–66 %) was observed in summer, which may be mainly explained by secondary OA (SOA) formation processes involving biogenic gaseous precursors. Conversely, high concentrations and OA contributions (32 %–62 %) of MO-OOA during winter and spring seasons were partly associated with anthropogenic emissions and/or long-range transport from northeastern Europe. The contribution of the different OA factors as a function of OA mass loading highlighted the dominant roles of POA during pollution episodes in fall and winter and of SOA for highest springtime and summertime OA concentrations. Finally, long-term trend analyses indicated a decreasing feature (of about −175 ng m−3 yr−1) for MO-OOA, very limited or insignificant decreasing trends for primary anthropogenic carbonaceous aerosols (BBOA and HOA, along with the fossil-fuel and biomass-burning black carbon components) and no statistically significant trend for LO-OOA over the 6-year investigated period.

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.

Changing supersites: assessing the impact of the southern UK EMEP supersite relocation on measured atmospheric composition

In January 2016 the United Kingdom’s southern European Monitoring and Evaluation Programme (EMEP) level-2 air pollution monitoring ‘supersite’ was relocated from Harwell, Oxfordshire to Chilbolton Observatory, Hampshire. As no co-location study was undertaken, this work retrospectively investigates whether the supersite relocation has led to discontinuities in the time series of concentrations of commonly studied gaseous pollutants (NOx, NH3, SO2 and O3) and particulate matter (PM2.5 and PM10). Two years of measurements pre- and post-relocation (2014–15 and 2016–17 respectively) were analysed in conjunction with meteorological variables and local emission data. The deweather package was applied to the concatenated time series to minimise the influence of meteorology. Similar average concentrations of PM2.5, PM10, SO2 and O3 were observed, but there were substantial differences in that of NOx and NH3 (increase by factors of ∼1.6 and ∼3, respectively). The considerably higher NH3 concentrations at Chilbolton are attributed to the close proximity of mixed farmland, in particular to a strong south-westerly source contributing to ∼50% of the annual average. NOx and PM concentrations in easterly winds arriving at Chilbolton are ∼2.7 and ∼1.5 times larger than at Harwell, from sources including the M3 motorway and Greater London. Westerly concentrations of NOx remain similar, therefore despite a higher frequency of westerly wind, annual mean concentrations are larger. Lower concentrations of PM arriving from the west result in similar annual averages. The secondary inorganic and black carbon components of PM were broadly similar between the sites. The differences in average NOx and NH3 at Chilbolton must be taken into account when considering long-term regional trends based on the southern UK supersite data.

Year-long variability of the fossil fuel and wood burning black carbon components at a rural site in southern Delhi outskirts

This study examines year-long (April 2015 – March 2016) measurements of black carbon (BC) concentrations acquired with a 7-wavelength Aethalometer (ΑΕ-42) at Panchgaon, in the southern Delhi outskirts. We assess the seasonality of BC concentrations and focus on the quantification of the relative contributions from fossil-fuel combustion (BCff) and wood burning (BCwb) on annual basis. Significant monthly, daily and diurnal variability in both BC components is found due to seasonal changes in the emission sources, dispersion conditions, and boundary-layer dynamics. The annual-mean BC concentration at 880 nm is 7.2 ± 0.3 μg m−3 (range of 0.09–38.6 μg m−3), exhibiting the highest values in winter (9.3 ± 0.7 μg m−3) and the lowest (4.6 ± 0.2 μg m−3) in summer monsoon. BCff (mean of 5.9 ± 0.2 μg m−3) is estimated to account for 81% of the BC mass on annual basis, while the BCwb ranges from 0.55 ± 0.06 μg m−3 in July to 2.7 ± 0.2 μg m−3 in December. The highest BCff/BC fraction is observed in April–June (~86–87% at 880 nm), while the BCwb/BC peaks in October–December (23–29% at 880 nm). The BCff contribution increases in the early-morning hours due to traffic, while the BCwb fraction peaks during the evening and night hours in winter, due to wood and waste material burning for heating. The BC diurnal pattern is highly affected by the mixing-layer height variations, leading to lower concentrations around noon, when the vertical mixing and dilution processes are the strongest. The WRF-Chem model simulations represent rather satisfactorily the BC concentrations and diurnal patterns in summer, but fail to reproduce the BC peaks during late post-monsoon and winter, suggesting the need for refinement of the BC emissions, simulations of local meteorology, and/or boundary-layer dynamics.

Retrieval of Aerosol Components Using Multi-Wavelength Mie-Raman Lidar and Comparison with Ground Aerosol Sampling

We verified an algorithm using multi-wavelength Mie-Raman lidar (MMRL) observations to retrieve four aerosol components (black carbon (BC), sea salt (SS), air pollution (AP), and mineral dust (DS)) with in-situ aerosol measurements, and determined the seasonal variation of aerosol components in Fukuoka, in the western region of Japan. PM2.5, PM10, and mass concentrations of BC and SS components are derived from in-situ measurements. MMRL provides the aerosol extinction coefficient (α), particle linear depolarization ratio (δ), backscatter coefficient (β), and lidar ratio (S) at 355 and 532 nm, and the attenuated backscatter coefficient (βatt) at 1064 nm. We retrieved vertical distributions of extinction coefficients at 532 nm for four aerosol components (BC, SS, AP, and DS) using 1α532 + 1β532 + 1βatt,1064 + 1δ532 data of MMRL. The retrieved extinction coefficients of the four aerosol components at 532 nm were converted to mass concentrations using the theoretical computed conversion factor assuming the prescribed size distribution, particle shape, and refractive index for each aerosol component. MMRL and in-situ measurements confirmed that seasonal variation of aerosol optical properties was affected by internal/external mixing of various aerosol components, in addition to hygroscopic growth of water-soluble aerosols. MMRL overestimates BC mass concentration compared to in-situ observation using the pure BC model. This overestimation was reduced drastically by introducing the internal mixture model of BC and water-soluble substances (Core-Gray Shell (CGS) model). This result suggests that considering the internal mixture of BC and water-soluble substances is essential for evaluating BC mass concentration in this area. Systematic overestimation of BC mass concentration was found during summer, even when we applied the CGS model. The observational facts based on in-situ and MMRL measurements suggested that misclassification of AP as CGS particles was due to underestimation of relative humidity (RH) by the numerical model in lidar analysis, as well as mismatching of the optical models of AP and CGS assumed in the retrieval with aerosol properties in the actual atmosphere. The time variation of lidar-derived SS was generally consistent with in-situ measurement; however, we found some overestimation of SS during dust events. The cause of this SS overestimation is mainly due to misclassifying internally mixing DS as SS, implying that to consider internal mixing between DS and water-soluble substances leads to better estimation. The time-variations of PM2.5 and PM10 generally showed good agreement with in-situ measurement although lidar-derived PM2.5 and PM10 overestimated in dust events.

Emission factors of black carbon and co-pollutants from diesel vehicles in Mexico City

Abstract. Diesel-powered vehicles are intensively used in urban areas for transporting goods and people but can substantially contribute to high emissions of black carbon (BC), organic carbon (OC), and other gaseous pollutants. Strategies aimed at controlling mobile emissions sources thus have the potential to improve air quality and help mitigate the impacts of air pollutants on climate, ecosystems, and human health. However, in developing countries there are limited data on the BC and OC emission characteristics of diesel-powered vehicles, and thus there are large uncertainties in the estimation of the emission contributions from these sources. We measured BC, OC, and other inorganic components of fine particulate matter (PM), as well as carbon monoxide (CO), nitrogen oxides (NOx), sulfur dioxide (SO2), ethane, acetylene, benzene, toluene, and C2-benzenes under real-world driving conditions for 20 diesel-powered vehicles encompassing multiple emission level technologies in Mexico City with the chasing technique using the Aerodyne mobile laboratory. Average BC emission factors ranged from 0.41–2.48 g kg−1 of fuel depending on vehicle type. The vehicles were also simultaneously measured using the cross-road remote sensing technique to obtain the emission factors of nitrogen oxide (NO), CO, total hydrocarbons, and fine PM, thus allowing for the intercomparison of the results from the two techniques. There is overall good agreement between the two techniques and both can identify high and low emitters, but substantial differences were found in some of the vehicles, probably due to the ability of the chasing technique to capture a larger diversity of driving conditions in comparison to the remote sensing technique. A comparison of the results with the US EPA MOVES2014b model showed that the model underestimates CO, OC, and selected VOC species, whereas there is better agreement for NOx and BC. Larger OC / BC ratios were found in comparison to ratios measured in California using the same technique, further demonstrating the need for using locally obtained diesel-powered vehicle emission factor database in developing countries in order to reduce the uncertainty in the emissions estimates and to improve the evaluation of the effectiveness of emissions reduction measures.

Influential factors affecting black carbon trends at four sites of differing distance from a major highway in Las Vegas.

Elevated air pollution levels adjacent to major highways are an ongoing topic of public health concern worldwide. Black carbon (BC), a component of particulate matter (PM) emitted by diesel and gasoline vehicles, was measured continuously via a filter-based light absorption technique over ~ 16 months at four different stations positioned on a perpendicular trajectory to a major highway in Las Vegas, NV. During downwind conditions (winds from the west), BC at 20 m from the highway was 32 and 60% higher than concentrations at 100 and 300 m from the roadway, respectively. Overall highest roadside (20-m site) BC concentrations were observed during the time period of 4 a.m.-8 a.m. under low-speed variable winds (3.02 μg/m3) or downwind conditions (2.84 μg/m3). The 20-m site BC concentrations under downwind conditions are 85% higher on weekday periods compared to weekends during the time period of 4 a.m.-8 a.m. Whereas total traffic volume was higher on weekdays versus weekends and differed by approximately 3% on weekdays versus weekends, similarly, the detected heavy-duty fraction was higher on weekdays versus weekends and differed by approximately 21% on weekdays versus weekend. Low wind speeds predominated during early morning hours, leading to higher BC concentrations during early morning hours despite the maximum traffic volume occurring later in the day. No noticeable impact from the airport or nearby arterial roadways was observed, with the 300-m site remaining the lowest of the four-site network when winds were from the east. Multivariate linear regression analysis revealed that heavy-duty traffic volume, light-duty traffic volume, wind speed, weekday versus weekend, surface friction velocity, ambient temperature, and the background BC concentration were significant predictors of roadside BC concentrations. Comparison of BC and PM2.5 downwind concentration gradients indicates that the BC component contributes substantially to the PM2.5 increase in roadside environments. These results suggest that BC is an important indicator to assess the contribution of primary traffic emissions to near-road PM2.5 concentrations, providing opportunities to evaluate the feasibility and effectiveness of mitigation strategies.