Urban Aerosol Research Articles

Determination of dicarboxylic acids in atmospheric aerosols using continuous aerosol sampler with on-line connected ion chromatography system

The aim of the presented study was to use a recently developed CGU-ACTJU-IC system for on-line determination of dicarboxylic acids (DCAs) in aerosols over short time periods involving aerosol sampling into deionized water using a Condensation Growth Unit – Aerosol Counterflow Two-Jets Unit (CGU-ACTJU) sampler, quantitative preconcentration of analytes and determination by ion chromatography (IC). The parameters of automated on-line preconcentration method, using two parallel preconcentration columns and piston pump, were optimized. Limits of detection of studied DCAs, i.e., oxalic, malonic, succinic, glutaric/adipic, pimelic, azelaic and maleic acid, were determined to 0.27, 0.92, 1.74, 0.82, 1.17, 1.41 and 0.48 ng m−3, respectively.The optimized method was used for the analysis of DCAs in urban aerosol in Brno in two campaigns: from 5th to 9th December 2016 and from 12th to 21st July 2017. The results obtained by the developed method were compared with two reference methods including sampling of aerosols on filters and subsequent analysis of DCAs by gas chromatography with mass spectrometry (GC/MS) or IC.The presented study describes an alternative on-line method, compared to filter sampling, for monitoring of DCAs in atmospheric aerosols, allowing measurement with 1-h time resolution.

Polarimetric Radar Convective Cell Tracking Reveals Large Sensitivity of Cloud Precipitation and Electrification Properties to CCN

AbstractHypotheses have been proposed for decades about the effect of activated cloud condensation nuclei (CCN) on delaying the warm rain process, invigorating deep convective cloud vertical development, and enhancing mixed‐phase processes. Observational support has been only qualitative with mixed results due to the lack of regional measurements of CCN concentration (NCCN), while simulations have not produced a robust consensus. Quantitative assessments of these relationships became possible with the advent of NCCN retrievals from satellites; when combined with measurements by polarimetric radar and Lightning Mapping Array (LMA), tracking convective cells observed on radar and examining precipitation properties throughout the cells' life cycle has permitted the study of the impact of NCCN on cloud and precipitation characteristics. We composited more than 2,800 well‐tracked cells in the Houston region and stratified them by NCCN, convective available potential energy (CAPE), and urban/rural locations. The results show that increased NCCN invigorates the convection until saturation near NCCN = 1,000 cm3; increasing NCCN from ~400 to an optimum of ~1,000 cm3 increases lightning activity by an order of magnitude. A further increase in CCN decreases lightning rates. Adding CAPE enhances lightning only under low NCCN (e.g., less than 500 cm3). The presence of the urban area enhances lightning for similar NCCN concentrations, although this applies mainly under low NCCN conditions. The urban heat island as manifested by cloud base height cannot explain this observation. It is suspected that the urban ultrafine aerosols contribute to the storm electrification.

Monsoon Season Quantitative Assessment of Biomass Burning Clear-Sky Aerosol Radiative Effect at Surface by Ground-Based Lidar Observations in Pulau Pinang, Malaysia in 2014

Direct and indirect aerosol effects are still one of the largest uncertainties related to the Earth energy budget, especially in a wild and remote region like South-East Asia, where ground-based measurements are still difficult and scarce, while endemic cloudy skies make difficult active and passive satellite observations. In this preliminary study, we analyzed and quantitatively assessed the differences between monsoon and inter-monsoon seasons, in terms of radiative effects at surface and columnar heating rate, of clear-sky biomass burning aerosols (no clouds) using ground-based lidar observations obtained with a 355 nm elastic lidar instrument, deployed since 2012 at the Physics Department of Universiti Sains Malaysia (USM). The model-based back-trajectory analysis put in evidence that, during the monsoon seasons (November–March and June–September), the air masses advected towards the observational site transit over active fire hotspot regions, in contrast with the inter-monsoon season. In between the monsoon seasons (April–May, October), the atmosphere over Penang is constituted by local background urban aerosols that originate from road traffic emissions, domestic cooking, and industrial plants emissions. The analysis was carried out using the vertically-resolved profiles of the seasonal averaged aerosol optical properties (monsoon vs. inter-monsoon seasons), e.g., the atmospheric extinction coefficient, to evaluate the seasonal surface aerosol radiative effect and column heating rate differences through the Fu–Liou–Gu (FLG) radiative transfer model. The results put in evidence that the biomass burning advection during the monsoon season (especially during the South West monsoon from June to September) lowers the noon daytime incoming solar shortwave solar radiation reaching the Earth surface with respect to the local background conditions by 91.5 W/m2 (114–69 W/m2). The aerosols also lead to an averaged heating in the first kilometer of the atmosphere of about 4.9 K/day (6.4–3.4 W/m2). The two combined effects, i.e., less absorbed energy by Earth surface and warming of the first kilometer of the boundary layer, increase the low-level stability during monsoon seasons, with a possible reduction in cloud formation and precipitation. The net effect is to exacerbate the haze episodes, as the pollutants rest trapped into the boundary layer. Besides these considerations, the lidar measurements are of great interest in this particular world region and might be used for cal/val of the future space missions, e. g., Earthcare.

Urban Aerosol Particle Size Characterization in Eastern Mediterranean Conditions

Characterization of urban particle number size distribution (PNSD) has been rarely reported/performed in the Middle East. Therefore, we aimed at characterizing the PNSD (0.01–10 µm) in Amman as an example for an urban Middle Eastern environment. The daily mean submicron particle number concentration (PNSub) was 6.5 × 103–7.7 × 104 cm−3 and the monthly mean coarse mode particle number concentration (PNCoarse) was 0.9–3.8 cm−3 and both had distinguished seasonal variation. The PNSub also had a clear diurnal and weekly cycle with higher concentrations on workdays (Sunday–Thursday; over 3.3 × 104 cm−3) than on weekends (below 2.7 × 104 cm−3). The PNSub constitute of 93% ultrafine fraction (diameter < 100 nm). The mean particle number size distributions was characterized with four well-separated submicron modes (Dpg,I, Ni): nucleation (22 nm, 9.4 103 cm−3), Aitken (62 nm, 3.9 103 cm−3), accumulation (225 nm, 158 cm−3), and coarse (2.23 µm, 1.2 cm−3) in addition to a mode with small geometric mean diameter (GMD) that represented the early stage of new particle formation (NPF) events. The wind speed and temperature had major impacts on the concentrations. The PNCoarse had a U-shape with respect to wind speed and PNSub decreased with wind speed. The effect of temperature and relative humidity was complex and require further investigations.

Aerosol Optical Depth of the Main Aerosol Species over Italian Cities Based on the NASA/MERRA-2 Model Reanalysis

The Modern-Era Retrospective Analysis for Research and Applications, version 2 (MERRA-2) provides data at 0.5° × 0.625° resolution covering a period from 1 January 1980 to the present. Natural and anthropogenic aerosols are simulated in MERRA-2, considering the Goddard chemistry, aerosol, radiation, and transport model. This model simulates the sources, sinks, and chemistry of mixed aerosol tracers: dust, sea salt, hydrophobic and hydrophilic black carbon and organic carbon, and sulfate. MERRA-2 aerosol reanalysis is a pioneering tool for investigating air quality issues, noteworthy for its global coverage and its distinction of aerosol speciation expressed in the form of aerosol optical depth (AOD). The aim of this work was to use the MERRA-2 reanalysis to study urban air pollution at a national scale by analyzing the AOD. AOD trends were evaluated for a 30-year period (1987–2017) over five Italian cities (Milan, Rome, Cagliari, Taranto, and Palermo) in order to investigate the impacts of urbanization, industrialization, air quality regulations, and regional transport on urban aerosol load. AOD evolution predicted by the MERRA-2 model in the period 2002–2017 showed a generalized decreasing trend over the selected cities. The anthropogenic signature on total AOD was between 50% and 80%, with the largest contribution deriving from sulfate.

Characteristics and potential source areas of aliphatic amines in PM2.5 in Yangzhou, China

As highly hydrophilic basic compounds, amines are an important part of the earth's nitrogen cycle and closely related to human health. In this study, a few major low molecular weight alkyl aminium species, including methylaminium (MA), dimethylaminium (DMA) and ethylaminium (EA) in Yangzhou urban aerosols from April to November 2016 were measured and their mean concentrations in aerosols were determined to be 1.418 ± 1.341, 3.623 ± 3.941 and 12.576 ± 10.446 ng/m3, respectively, with higher concentrations in Spring. The total mass percentage of three aminium species to water-soluble organic nitrogen (WSON) were 0.01–5.74% and fraction of EA was highest (0.01–5.02%). The air mass trajectory and potential source contribution analyses indicate that the source of amines in Yangzhou aerosols was mainly from oceans and surrounding provinces, while the Yangtze River Delta region itself had relative little contribution.

Roles of Relative Humidity in Aerosol Pollution Aggravation over Central China during Wintertime.

Aerosol pollution elicits considerable public concern due to the adverse influence on air quality, climate change, and human health. Outside of emissions, haze formation is closely related to meteorological conditions, especially relative humidity (RH). Partly due to insufficient investigations on the aerosol hygroscopicity, the accuracy of pollution prediction in Central China is limited. In this study, taking Wuhan as a sample city, we investigated the response of aerosol pollution to RH during wintertime based on in-situ measurements. The results show that, aerosol pollution in Wuhan is dominated by PM2.5 (aerodynamic particle size not larger than 2.5 μm) on wet days (RH ≥ 60%), with the averaged mass fraction of 0.62 for PM10. Based on the RH dependence of aerosol light scattering (f (RH)), aerosol hygroscopicity was evaluated and shows the high dependence on the particle size distribution and chemical compositions. f (RH = 80%) in Wuhan was 2.18 (±0.73), which is comparable to that measured in the Pearl River Delta and Yangtze River Delta regions for urban aerosols, and generally greater than values in Beijing. Ammonium (NH4+), sulfate (SO42−), and nitrate (NO3−) were enhanced by approximately 2.5-, 2-, and 1.5-fold respectively under wet conditions, and the ammonia-rich conditions in wintertime efficiently promoted the formation of SO42− and NO3−, especially at high RH. These secondary ions play an important role in aggravating the pollution level and aerosol light scattering. This study has important implications for understanding the roles of RH in aerosol pollution aggravation over Central China, and the fitted equation between f (RH) and RH may be helpful for pollution forecasting in this region.

CHARACTERIZATION OF SPRING AIR POLLUTION OF BEIJING IN 2019 USING ACTIVE AND PASSIVE REMOTE SENSING INSTRUMENTS

Abstract. As the capital of China, the Beijing area needs to be paid special attention to its air quality. We used active remote sensing instrument (ground-based lidar), combined with passive remote sensing instrument (VIIRS onboard the NPP spacecraft), to study the serious pollution event over Beijing in spring of 2019. At the same time, the ground-based particulate matter (PM) data and the meteorological element data were analyzed. It is found that the ratio of concentrations of PM2.5 to PM10 is very large during the pollution period. The mean value of ratio is 0.75464, indicated it is fine particulate matter pollution. The Range correction signal (RCS) of lidar is very large in the layer below 0.5 km. But the volume depolarization ratio (VDR) is much less than 0.05. It indicated it is anthropogenic urban aerosols. The change in the aerosol optical depth (AOD) of VIIRS during pollution is consistent with the change in optical properties observed by lidar. The backward trajectory model of HYSPLIT shows that the pollutant came from the Hebei area where industrial pollution is serious, and the local meteorological conditions in Beijing are conducive to the continuous accumulation of pollutants. This work can deepen the understanding of the mechanism of haze formation and can help and support pollution prevention work.

SATELLITE-DERIVED AIR POLLUTANTS AND THEIR CORRELATIONS WITH URBAN FORM IN GUANGDONG, CHINA

Abstract. The ways cities grow and evolve spatially are crucial factors which affect urban aerosol pollution. Understanding the spatial distribution of air pollutants and their correlations with urban form is of great significance to the improvement of urban atmospheric environment and regional sustainable development of urbanization. In this study, we firstly examined the spatial variations of satellite-derived PM2.5 and NO2 and urban form metrics in Guangdong, and also explored their relationships. The results indicated that the highest and lowest values of PM2.5 and NO2 mainly occur over the Pearl River Delta (PRD) region, and over the eastern Guangdong, respectively. For the size and shape of urban patches, urban form had significant effects on air pollutants in Guangdong. PM2.5 was positively correlated with AREA_AM, CA and SHAPE_AM, and NO2 was positively correlated with LPI, PLAND and AREA_AM, while both of them were negatively related to PARA _AM and ENN_AM. It is inferred that polycentric urban form was associated with low PM2.5 and NO2 concentration, and reasonable urban planning would help mitigate the fine particle pollution.

The relationship between aerosol concentration and atmospheric potential gradient in urban environments.

Urban aerosol is a growing concern for people living within cities; aerosol have been implicated in many ill health conditions, including that of the lung and of the heart. Atmospheric potential gradient is a consequence of charge carried to the ionosphere through thunderstorms, and its value depends on highly electrically mobile ion concentrations, hence local conductivity of the air. Ions attach to aerosol in the atmosphere, reducing their mobility and therefore increasing the potential gradient, and so potential gradient measurements have been suggested as a proxy for aerosol measurements. Particle number count, size distribution and potential gradient were measured for two campaigns in Manchester, U.K., and one campaign in Bristol, U.K. Using a factor based on size distribution to account for preferential attachment at larger sizes provided the best relationship with potential gradient, but particle count alone showed a weaker, but similar relationship. The increase in particle count caused by annual bonfire and fireworks celebrations (November) was evidenced in both potential gradient and particle numbers. Daily regression or correlation did not show a consistent relationship. In the larger Bristol data set, increasing humidity led to a reduction of potential gradient, while increasing particle number led to an increase.

Comparative study on water-soluble inorganic ions in PM2.5 from two distinct climate regions and air quality

Recently, air quality has significantly improved in developed country, but that issue is of concern in emerging megacity in developing country. In this study, aerosols and their precursor gas were collected by NILU filter pack at two distinct urban sites during the winter and summer in Osaka, Japan and dry and rainy seasons in Ho Chi Minh City (HCMC), Vietnam. The aims are to investigate the contribution of water-soluble inorganic ions (WSIIs) to PM2.5, thermodynamic characterization and possible formation pathway of secondary inorganic aerosol (SIA). The PM2.5 concentration in Osaka (15.8 μg/m3) is lower than that in HCMC (23.0 μg/m3), but the concentration of WSIIs in Osaka (9.0 μg/m3) is two times higher than that in HCMC (4.1 μg/m3). Moreover, SIA including NH4+, NO3− and SO42− are major components in WSIIs accounting for 90% and 76% (in molar) in Osaka and HCMC, respectively. Thermodynamic models were used to understand the thermodynamic characterization of urban aerosols. Overall, statistical analysis results indicate that very good agreement (R2 > 0.8) was found for all species, except for nitrate aerosol in HCMC. We found that when the crustal species present at high amount, those compositions should be included in model calculation (i.e. in the HCMC situation). Finally, we analyzed the characteristics of NH4+– NO3−– SO42− system. A possible pathway to produce fine nitrate aerosol in Osaka is via the homogeneous reaction between NH3 and HNO3, while non-volatile nitrate aerosols can be formed by the heterogeneous reactions in HCMC.

Urban and rural coarse aerosol mass across the United States: Spatial and seasonal variability and long-term trends

Coarse aerosol mass (CM = PM10 − PM2.5, mass of particles with aerodynamic diameters between 2.5 and 10 μm) has important environmental and climate impacts. Examining the spatial and temporal variability of CM is important for understanding its sources and transport, evaluating its environmental impacts, and designing mitigation strategies. CM was computed at 195 collocated U.S. Environmental Protection Agency (EPA) PM10 and PM2.5 Federal Reference Method (FRM) sites from 2000 through 2016. These data were integrated with remote/rural CM data at 155 sites from the IMPROVE (Interagency Monitoring of Protected Visual Environments) network to create a continental-scale dataset of daily, monthly, seasonal, and annual mean CM concentrations, as well as regionally aggregated data. Annual mean average continental United States (CONUS) urban CM concentrations were twice that of rural CM concentrations (10.5 μg m−3 versus 4.9 μg m−3, respectively) for 2012–2016. The highest CM concentrations occurred in the Southwest in spring, the central United States in summer and fall, and southern California nearly year-round. The lowest CM concentrations occurred in the Intermountain West, northwestern United States, and regions in the East. While urban CM concentrations were higher, CONUS average urban and rural CM/PM10 fractions were similar, with an annual mean fraction of 0.5. However, many regions, especially across the West, experienced much higher fractions (>0.7) depending on season. Regional mean CM weekly cycles with lower weekend concentrations were observed at both urban and rural sites throughout most of the country, indicating anthropogenic influence. Trend analyses suggest spring and summer mean CM has increased significantly at some remote and urban sites over the 2000–2016 period, especially at sites in the central and eastern United States. However, CONUS annual mean urban CM has decreased significantly (p < 0.05) at a rate of −1.8% yr−1 compared to an insignificant increase of 0.5% yr−1 at rural sites. Urban and rural relative contributions of CM to PM10 have increased since 2000 due to the strong reductions of PM2.5 mass. Understanding CM seasonal and temporal variability, composition, and sources is increasingly important in order to develop effective mitigation strategies for managing its environmental and climate impacts.

Regional Inhaled Deposited Dose of Urban Aerosols in an Eastern Mediterranean City

We calculated the regional deposited dose of inhaled particulate matter based on number/mass concentrations in Amman, Jordan. The dose rate was the highest during exercising but was generally lower for females compared to males. The fine particles dose rate was 1010–1011 particles/h (101–102 µg/h). The PM10 dose rate was 49–439 µg/h for males and 36–381 µg/h for females. While resting, the PM10 deposited in the head airways was 67–77% and 8–12% in the tracheobronchial region. When exercising, the head airways received 37–44% of the PM10, whereas the tracheobronchial region received 31–35%. About 8% (exercise) and 14–16% (rest) of the PM2.5 was received in the head airways, whereas the alveolar received 74–76% (exercise) and 54–62% (rest). Extending the results for common exposure scenarios in the city revealed alarming results for service workers and police officers; they might receive PM2.5 and 220 µg/h PM10 while doing their duty on main roads adjacent to traffic. This is especially critical for a pregnant police officer. Outdoor athletic activities (e.g., jogging along main roads) are associated with high PM2.5 and PM10 dose rates (100 µg/h and ~425 µg/h, respectively).

Large contribution of fine carbonaceous aerosols from municipal waste burning inferred from distributions of diacids and fatty acids

To investigate the origins, other than fossil fuel combustion and biomass burning, of urban carbonaceosus aerosols, we studied the fine (PM2.5) aerosols collected in Guiyang, Southwest China in winter (December 10–23) 2012 for organic carbon (OC), elemental carbon (EC) and water-soluble diacids, oxoacids, α-dicarbonyls and fatty acids as well as inorganic ions. Oxalic acid (C2) found to be the most abundant diacid species followed by succinic (C4) and terephthalic (t-Ph) acids, respectively. Even-carbon numbered fatty acids showed high abundances with a peak at C16. OC, EC and most of diacids and related compounds, but not inorganic ions, showed a similar temporal pattern with a drastic rise in December 15 day- and night-time samples during the campaign. Based on molecular distributions of diacids and fatty acids, and linear relations of OC and EC with selected marker ions and diacid species, we found that the organics and EC in PM2.5 are mainly derived from higher plant/cooking and municipal waste burning emissions in Guiyang. This study implies that municipal waste burning largely contributes to carbonaceous aerosols and warrants a need of further research on its role in aerosol loading and air quality in the urban atmosphere.

Compound-Specific Stable Carbon Isotope Ratios of Terrestrial Biomarkers in Urban Aerosols from Beijing, China

Molecular compositions and stable carbon isotope ratios (δ13C) of n-alkanes and fatty acids (FA) were investigated in urban aerosols from Beijing, China. Seasonal trends for n-alkanes showed a high...

Evidence of association between aerosol properties and in-vitro cellular oxidative response to PM1, oxidative potential of PM2.5, a biomarker of RNA oxidation, and its dependency on combustion sources

The causal link between ambient PM2.5 and adverse health effects is still not clear enough, nor it is clear what factors (physical and/or chemical) contribute to PM2.5 toxicity and by what mechanism(s). With a view on this, we launched the CARE experiment, during which we performed a comprehensive characterisation of the physicochemical properties of fine and ultrafine particles under exposure levels dominated by the urban combustion aerosol, and their toxicological assessment through in-vitro tests (lung epithelia cells cultured at the ALI) directly under ambient conditions, oxidative potential (determined through 2′,7′-dichlorouorescin, OPDCFH), and human biomonitoring. We already reported about aerosol characterisation, and in-vitro model results during CARE. Building upon these, in this work we assess the combustion aerosol oxidative response through the analysis of consistency between the three independent aerosol oxidative responses obtained, and the exploration of any causality link with the combustion aerosol. This is the first time to our knowledge that combustion related PM2.5 physicochemical properties and its OPDCFH are compared to the cellular-oxidative response (C-OR) obtained through the PM in-vitro test carried out (for the first time) directly under atmospheric ambient conditions, and to certain biomarkers of oxidative damage to DNA/RNA (8-oxo-7,8-dihydroguanine, 8-oxo-7,8-dihydro-2′-deoxyguanosine and 8-oxo-7,8 - dihydroguanosine). Our results provide a first evidence of a combustion-dependent association between the in vitro C-OR, the PM2.5 OPDCFH, and the urinary excretion of the 8-Oxo-7,8-dihydroguanosine. Yet this is not a substantial basis for drawing any cause-effect relationship. However, our findings support previous literature suggesting a link between combustion and oxidative response of PM2.5. Moreover, we add a consistency across completely independent oxidative response measurements with a possible dependence on the combustion traffic-related aerosol. This is a piece of information that may have important implications in the understanding of how combustion sources contribute to oxidative response related diseases.

Urban Aerosol Hygroscopicity During Haze Weather

The hygroscopicity of aerosols has an important influence on atmospheric visibility and is one of the main causes of haze pollution. Based on observations of the aerosol hygroscopic growth factor (GF), water soluble inorganic ions, and organic carbon/elemental carbon (OC/EC) data during haze weather from April 17 to May 21, in 2014, the hygroscopic properties of aerosols and corresponding effects on haze in Nanjing were analyzed. The results showed that the distribution of GF was bimodal and varied from 1.12 to 1.64. With the increase of particle size, the average hygroscopic growth factor (GFmean) changed less and the standard deviation of wettability (σ) increased gradually; meanwhile, the degree of external mixing of chemical components increased gradually. The hygroscopicity of aerosol particles in the day was better than that at night, but the mixing degree was weaker than that at night; in non-haze weather, the hygroscopicity of aerosol particles was stronger and the degree of external mixing was higher, while the hygroscopicity and mixing degree of haze particles showed opposite trends. With the increase of haze levels, the hygroscopicity of aerosol particles grew weaker and the degree of external mixing decreased further. Relative humidity can have a significant impact on the chemical components of aerosols and their hygroscopic capacity. Under a low humidity background, the main chemical components of aerosols included NH4+, NO3-, SO42-, OC, and EC, and the content of OC/EC in aerosols during haze days was more abundant; in haze weather with low relative humidity, abundant organic matter was the main reason for the decrease of the moisture absorption capacity of small-scale aerosols. The level of relative humidity in the haze weather was also an important factor affecting the hygroscopic capacity of aerosols. The contents of (NH4)2SO4, OC, and insoluble substances in aerosols were the highest, followed by NH4NO3. The contents of these chemical components showed obvious diurnal variation characteristics, which resulted in significant diurnal variation of the hygroscopicity of the aerosols. κchem calculated by the chemical composition and κmean acquired by observations using H-TDMA showed good consistency, and the correlation coefficient was 0.8903. In haze weather, the correlation between them was further enhanced. Therefore, the major chemical components of aerosols could be used to predict the hygroscopic properties of aerosols.

Impact of anthropogenic and biogenic sources on the seasonal variation in the molecular composition of urban organic aerosols: a field and laboratory study using ultra-high-resolution mass spectrometry

Abstract. This study presents the molecular composition of organic aerosol (OA) using ultra-high-resolution mass spectrometry (Orbitrap) at an urban site in Central Europe (Zurich, Switzerland). Specific source spectra were also analysed, including samples representative of wood-burning emissions from Alpine valleys during wood-burning pollution episodes and smog chamber investigations of woodsmoke, as well as samples from Hyytiälä, which were strongly influenced by biogenic secondary organic aerosol. While samples collected during winter in Alpine valleys have a molecular composition remarkably similar to fresh laboratory wood-burning emissions, winter samples from Zurich are influenced by more aged wood-burning emissions. In addition, other organic aerosol emissions or formation pathways seem to be important at the latter location in winter. Samples from Zurich during summer are similar to those collected in Hyytiälä and are predominantly impacted by oxygenated compounds with an H∕C ratio of 1.5, indicating the importance of biogenic precursors for secondary organic aerosol (SOA) formation at this location (summertime Zurich – carbon number 7.6, O:C 0.7; Hyytiälä – carbon number 10.5, O:C 0.57). We could explain the strong seasonality of the molecular composition at a typical European site by primary and aged wood-burning emissions and biogenic secondary organic aerosol formation during winter and summer, respectively. Results presented here likely explain the rather constant seasonal predominance of non-fossil organic carbon at European locations.

Comparison of size-resolved hygroscopic growth factors of urban aerosol by different methods in Tianjin during a haze episode

Size-resolved hygroscopic growth factors of urban aerosol during a haze episode were measured using a Humidified Tandem Differential Mobility Analyzer (HTDMA) (gm(RH)). These factors were also derived from size-resolved particulate chemical composition combined with the κ-Köhler theory (gκ(RH)) and the thermodynamic model ISORROPIA-II running in forward mode (giso-f(RH)) and reverse mode (giso-r(RH)), respectively. In terms of agreement among these hygroscopic growth factors, gκ(RH) matched gm(RH) best, followed by giso-r(RH). In contrast, giso-f(RH) demonstrated a poorer agreement with gm(RH). The good consistency among gm(RH), gκ(RH), and giso-r(RH) was because they only focus on the physical hygroscopic process, whereas giso-f(RH) contains not only the direct influence of relative humidity (RH) on particle size but also the influence of gaseous precursor on the particle chemical composition, which indirectly affects the hygroscopicity of the particles. In this sense, size-resolved gκ(RH) and giso-r(RH) in a wide size range are more adequate to investigate the impact of RH on light scattering and aerosol radiative forcing. At RH = 80%, gκ(RH) for accumulation mode particles was 1.30–1.45 on polluted days and higher than that on clean days (1.2–1.3). Whereas on both polluted and clean days, gκ(RH) of ultrafine and coarse mode particles were generally lower than 1.25. The strong hygroscopicity of accumulation mode particles observed on polluted days can deteriorate visibility due to their high extinction efficiency.

Characterization of urban aerosol: Seasonal variation of genotoxicity of the water-soluble portion of PM2.5 and PM1

Urban particulate matter (PM) is a complex mixture of several classes of chemicals: elemental carbon, ammonium, sulfates, nitrates, organic compounds and metals. For a long time, numerous studies had shown that PM causes health problems and, in 2013, it has been classified by the International Agency for Research on Cancer as carcinogenic to humans (group 1). Furthermore, it’s known that the fine fraction of PM is the most genotoxic, and that smaller particles are retained by the lower respiratory system, making fine particles a public health concern. In this study we characterize the water-soluble portion of urban aerosol from Bologna, a county town of Emilia-Romagna in the north of Italy, by collecting the finest fractions of airborne particles, PM2.5 and PM1, in three different seasons (winter, summer and autumn) over a three-year period. The genotoxicity of the water-soluble extracts was evaluated, both by a standard and a enzyme-modified Comet assay and also by the Micronucleus test, with lung adenocarcinoma epithelial cells (A549). In the same extracts, water-soluble metals (V, Ni, Cu, Cr, Fe) were detected and associations between the physicochemical parameters of PM and genotoxicity were evaluated. DNA strand breaks were found in summer and winter samples in the Comet experiments, whereas oxidative damage was induced by autumn extracts; winter samples induced chromosome breakage or loss in A549 cells. Iron and copper were the most abundant transition metals in both fractions and both were associated with micronuclei induction, whereas chromium is linked with oxidative damage. This study also shows that the water-soluble fraction of PM contributes to global genotoxicity and that transition metals play a role, therefore both organic and water-soluble fractions should be considered in an air-quality monitoring program.