Light absorbing aerosols (LAA) absorb sunlight and heat the atmosphere. This work presents a novel methodology to experimentally quantify the heating rate (HR) induced by LAA into an atmospheric ...layer. Multiwavelength aerosol absorption measurements were coupled with spectral measurements of the direct, diffuse and surface reflected radiation to obtain highly time-resolved measurements of HR apportioned in the context of LAA species (black carbon, BC; brown carbon, BrC; dust), sources (fossil fuel, FF; biomass burning, BB), and as a function of cloudiness. One year of continuous and time-resolved measurements (5 min) of HR were performed in the Po Valley. We experimentally determined (1) the seasonal behavior of HR (winter 1.83 ± 0.02 K day–1; summer 1.04 ± 0.01 K day–1); (2) the daily cycle of HR (asymmetric, with higher values in the morning than in the afternoon); (3) the HR in different sky conditions (from 1.75 ± 0.03 K day–1 in clear sky to 0.43 ± 0.01 K day–1 in complete overcast); (4) the apportionment to different sources: HRFF (0.74 ± 0.01 K day–1) and HRBB (0.46 ± 0.01 K day–1); and (4) the HR of BrC (HRBrC: 0.15 ± 0.01 K day–1, 12.5 ± 0.6% of the total) and that of BC (HRBC: 1.05 ± 0.02 K day–1; 87.5 ± 0.6% of the total).
Vehicle emissions are identified as a major source of air pollution in metropolitan areas. Emission control programs in many cities have been implemented as part of larger scale transport policy ...interventions to control traffic pollutants and reduce public health risks. These interventions include provision of traffic-free and low emission zones and congestion charging. Various studies have investigated the impact of urban street configurations, such as street canyon in urban centers, on pollutants dispersion and roadside air quality. However, there are few investigations in the literature to study the impact of change of fleet composition and street canyon effects on the on-road pollutants concentrations and associated roadside pedestrian exposure to the pollutants. This study presents an experimental investigation on the traffic related gas and particle pollutants in and near major streets in one of the most developed business districts in Hong Kong, known as Central. Both street canyon and open roadway configurations were included in the study design. Mobile measurement techniques were deployed to monitor both on-road and roadside pollutants concentrations at different times of the day and on different days of a week. Multiple traffic counting points were also established to concurrently collect data on traffic volume and fleet composition on individual streets. Street canyon effects were evident with elevated on-road pollutants concentrations. Diesel vehicles were found to be associated with observed pollutant levels. Roadside black carbon concentrations were found to correlate with their on-road levels but with reduced concentrations. However, ultrafine particles showed very high concentrations in roadside environment with almost unity of roadside/on-road ratios possibly due to the accumulation of primary emissions and secondary PM formation. The results from the study provide useful information for the effective urban transport design and bus route reorganization to minimize the impact of traffic emissions on the urban air quality and public health. Observations on the elevated ultrafine particle concentrations in roadside pedestrian levels also demonstrate the urgent need to improve roadside air quality to reduce pedestrians’ health risks especially inside street canyon.
•Mobile measurements were used to assess urban air quality and pedestrian exposure.•Traffic impact on street canyon and roadside air quality was investigated.•Formation of ultrafine particles in roadside environments was observed.•Transport policy needs to consider traffic volume and composition in urban canyon.
Abstract
Atmospheric black carbon (BC) has a strong positive, but still controversial, effect on global warming. In particular, BC absorption enhancement (
E
abs
) due to internal mixing with other ...chemical species—so-called lensing effect—is poorly assessed. This bottleneck partly relies on the lack of long-term in situ measurements of both the optical and chemical properties of BC-containing particles. Here, we present experimental and computational results showing a significant
E
abs
increase with the aerosol photochemical aging. This was associated with the production of highly oxidized secondary organic aerosols (SOA), especially at summertime. The 3-year-long continuous aerosol chemical and optical measurements used for the present study was obtained in the Paris region, France, which might be representative of near-future air quality within developing countries. These findings suggest that SOA could represent one of the most critical chemical species to be considered within climate models.
Inhaled aerosolized particulate matter (PM) induces cellular oxidative stress in
vivo, leading to adverse health outcomes. The oxidative potential (OP) of PM
appears to be a more relevant proxy of ...the health impact of the aerosol rather
than the total mass concentration. However, the relative contributions of the
aerosol sources to the OP are still poorly known. In order to better quantify
the impact of different PM sources, we sampled aerosols in a French city for one
year (2014, 115 samples). A coupled analysis with detailed chemical
speciation (more than 100 species, including organic and carbonaceous compounds,
ions, metals and aethalometer measurements) and two OP assays (ascorbic acid, AA, and dithiothreitiol, DTT) in a simulated lung fluid (SLF) were performed
in these samples. We present in this study a statistical framework using a
coupled approach with positive matrix factorization (PMF) and multiple linear
regression to attribute a redox-activity to PM sources. Our results highlight
the importance of the biomass burning and vehicular sources to explain the
observed OP for both assays. In general, we see a different contribution of the
sources when considering the OP AA, OP DTT or the mass of the
PM10. Moreover, significant differences are observed between
the DTT and AA tests which emphasized chemical specificities of the two tests
and the need of a standardized approach for the future studies on
epidemiology or toxicology of the PM.
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.
•A simple methodology to determine and verify traffic emissions in a city is presented.•The first time the Aethalometer model was used to evaluate the emission inventory results.•The verified model was used to model emission reduction scenarios.•Removing 10% of highest polluting vehicles reduces BC emissions by 39% and NOx by 33%.
Traffic restrictions are an unpopular tool to mitigate urban air pollution, and a measurable improvement in air quality is needed to demonstrate the effectiveness of this measure. Previous attempts ...failed to detect measurable reductions of PM mass pollution within the areas subject to traffic restriction. However black carbon, which is emitted primarily by traffic sources, could be a PM metric more suitable than PM mass to demonstrate pollutant reductions. In this study we report the results of a black carbon monitoring campaign carried out in Milan, Italy, with the aim to detect - and demonstrate more suitably than PM mass - differences in local urban air quality among three zones located very closely with different traffic intensity. The study was carried out in three different days by measuring simultaneously black carbon and PM mass concentrations with fixed monitoring stations located in three main radial roads connecting the outskirts to the city center, each with three segments: 1) an outer one, with no traffic restrictions 2) an intermediate one, subject to the congestion traffic charge called “Ecopass”, where a ticket is required to enter for cars equipped with engines prior to Euro 4 standard; 3) the pedestrian zone (no cars admitted) of Duomo Square in the city center, where each of the three main roads ends. The results demonstrated a sharply declining gradient in black carbon levels from the outer zone, without traffic restrictions, to the more central areas, for all of the three radial main roads. The differences in mean black carbon levels in the same day in the different traffic scheme locations were highly significant for each comparison. In contrast to the Black carbon results, mean PM
10, PM
2.5, PM
1 concentrations did not show significant differences among the different traffic zones on the different campaign days. The ratio of black carbon to PM
10 decreased by 47% and 62% in the Ecopass zone and in the pedestrian zone, respectively, as compared to the no-restriction zone. To the best of our knowledge this is the first study showing that within-city proximal areas with different traffic intensity are associated with different black carbon levels. These data suggest that black carbon is a highly relevant metric of traffic pollution and should be taken into consideration in demonstrating the effectiveness of air quality mitigation measures.
► The Ecopass zone is a traffic restriction zone for diesel vehicles in Milan. ► Black carbon concentrations were reduced in the Ecopass zone. ► In contrast, no difference in PM mass concentrations was observed. ► Black carbon is a powerful metric for evaluating traffic restriction impact.
We compared two approaches (denoted as Virkkula” and “Drinovec” equations) for the determination of black carbon via attenuation measurements with a transmissometer OT-21 (Magee Scientific) on quartz ...fiber filters from different station types (urban-traffic, rural-background and remote) within the Austrian air monitoring network. First, we evaluated the entire data set to compare the performance of the models in the determination of the loading parameter k and the mass attenuation cross section σ. Then we investigate k and σ for different station types. The data set comprises 299 filters, all representative for 24 h samples collected with High-Volume-Samplers. Mass concentrations ranged from approximately 5-100 μg m−3 and covered all seasons.
Both approaches give statistically indistinguishable results of k with values of 1.00*10−3 ( ±2*10−4) and 0.97*10−3 ( ±1*10−4), respectively, if the entire data set is evaluated. The “Drinovec” approach gives slightly lower values for σ than “Virkkula” with values of 32.1 m2 g−1 ( ±1.1 m2 g−1) and 35.3 m2 g−1 ( ±1.9 m2 g−1). If the data set is restricted to ATN<300 only, no statistically relevant changes are obtained for k and σ using the “Virkkula” equation. Applying the “Drinovec” equation both parameters, k and σ increase when the data set is restricted.
The investigation of the different station types yields values of k statistically not different from zero, whereas σ values are different for the respective station types. Highest values of σ = 33.7 m2 g−1 ( ±1.4 m2 g−1) were observed for the remote, followed by σ = 31.8 m2 g−1 ( ±0.5 m2 g−1) for the rural-background station and lowest values of σ = 24.4 m2 g−1 ( ±0.5 m2 g−1) for the urban-traffic stations, possibly reflecting the respective aerosol type.
Based on the results for k and σ using either overall values or station type specific values we performed an extensive validation, discussing the application of the transmissometer measurements for a quick, easy and non-destructive quantification of eBC on either fresh sampled or archived filters of different station types. Applying the method for stations not classified as urban, rural or remote a deviation of eBC and EC values up to 23% can be expected. If the station type is known and the respective k and σ values are used this deviation goes down to 10% or lower. This would allow users to obtain long-term time-series going back to times when no on-line instruments were existing, and to obtain these data sets for sites where no on-line instruments are installed even now.
•eBC and EC concentrations deviate less than 10% if station types are considered.•Different filter loading effect models were found to be statistically equal.•The filter loading parameter k is statistically not different from zero for single station types.•σ values decrease from remote to rural-background to urban-traffic aerosols.
Brown carbon (BrC) is known to absorb light at subvisible wavelengths but its optical properties and sources are still poorly documented, leading to large uncertainties in climate studies. Here, we ...show its major wintertime contribution to total aerosol absorption at 370 nm (18–42%) at 9 different French sites. Moreover, an excellent correlation with levoglucosan (r2 = 0.9 and slope = 22.2 at 370 nm), suggesting important contribution of wood burning emissions to ambient BrC aerosols in France. At all sites, BrC peaks were mainly observed during late evening, linking to local intense residential wood burning during this time period. Furthermore, the geographic origin analysis also highlighted the high potential contribution of local and/or small-regional emissions to BrC. Focusing on the Paris region, twice higher BrC mass absorption efficiency value was obtained for less oxidized biomass burning organic aerosols (BBOA) compared to more oxidized BBOA (e.g., about 4.9 ± 0.2 vs. 2.0 ± 0.1 m2 g−1, respectively, at 370 nm). Finally, the BBOA direct radiative effect was found to be 40% higher when these two BBOA fractions are treated as light-absorbing species, compared to the non-absorbing BBOA scenario.
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•High contribution of brown carbon to aerosol absorption was observed at nine locations in France during winter.•Major sources of brown carbon were attributed to wood burning emissions from residential heating.•Mass absorption cross section of less oxidized BBOA was higher than that of the more oxidized.
We present results from a systematic study of vertical profiles of aerosol number size distribution and black carbon (BC) concentrations conducted in the Arctic, over Ny-Ålesund (Svalbard). The ...campaign lasted 2 years (2011–2012) and resulted in 200 vertical profiles measured by means of a tethered balloon (up to 1200 m a.g.l.) during the spring and summer seasons. In addition, chemical analysis of filter samples, aerosol size distribution and a full set of meteorological parameters were determined at ground. The collected experimental data allowed a classification of the vertical profiles into different typologies, which allowed us to describe the seasonal phenomenology of vertical aerosol properties in the Arctic. During spring, four main types of profiles were found and their behavior was related to the main aerosol and atmospheric dynamics occurring at the measuring site. Background conditions generated homogenous profiles. Transport events caused an increase of aerosol concentration with altitude. High Arctic haze pollution trapped below thermal inversions promoted a decrease of aerosol concentration with altitude. Finally, ground-based plumes of locally formed secondary aerosol determined profiles with decreasing aerosol concentration located at different altitude as a function of size. During the summer season, the impact from shipping caused aerosol and BC pollution plumes to be constrained close to the ground, indicating that increasing shipping emissions in the Arctic could bring anthropogenic aerosol and BC in the Arctic summer, affecting the climate.
On-road measurements of traffic-related gas and particle pollutant concentrations in three tunnels in Hong Kong and high resolution pollutant concentration profiles obtained while driving through the ...tunnels were used to derive the individual pollutant gradients using parametric and non-parametric (Sen–Thiel) slopes and compared with the commonly used entrance-exit two points calculation. The fuel based emission factors of measured pollutants for individual tunnels at different times of day were derived from gradients using a new method based on fuel carbon balance principle. Combined with the tunnel traffic volume and composition, the average tunnel emission factors were analyzed by linear regression to derive the diesel fleet emission factors. Average nitrogen oxides (NOx) and black carbon (BC) emission factor for diesel fleets are 29.3 ± 11.0 gNO2 kg−1 and 1.28 ± 0.76 g kg−1 of fuel, respectively. The results from the study were compared with the emission data from vehicle chasing approaches and the literature, showing reasonable agreement. Practical limitations and future direction for improvement of our method were also discussed. The method presented in this study provides a convenient drive-through approach for fast determination of tunnel and individual vehicle fleet emission factors. It can be used as an effective and fast approach to validate the emission inventory and to evaluate the effectiveness of policy intervention on the traffic emissions.
•Drive-through approach is developed to determine tunnel emission factor.•Sen Slope method is less biased than entrance-exit approach.•Diesel fleet emission factor is obtained with bivariate regression.
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