Aged Sea Salt Research Articles

Characterization of the water soluble fraction in ultrafine, fine, and coarse atmospheric aerosol

Water soluble organic carbon significantly contributes to aerosol's carbon mass and its chemical composition is poorly characterized due to the huge number of species. In this study, we determined 94 water-soluble compounds: inorganic ions (Cl−, Br−, I−, NO3−, SO42−,K+, Mg+, Na+, NH4+, Ca2+), organic acids (methanesulfonic acid and C2-C7 carboxylic acids), monosaccharides, alcohol-sugars, levoglucosan and its isomers, sucrose, phenolic compounds, free l- and d-amino acids and photo-oxidation products of α-pinene (cis-pinonic acid and pinic acid). The sampling was conducted using a micro-orifice uniform deposit impactor (MOUDI) at the urban area of Mestre-Venice from March to May 2016. The main aim of this work is to identify the source of each detected compound, evaluating its particle size distribution. Clear differences in size distributions were observed for each class of analyzed compounds.The positive matrix factorization (PMF) model was used to identify six factors related to different sources: a) primary biogenic aerosol particles with particle size > 10 μm; b) secondary sulfate contribution; c) biomass burning; d) primary biogenic aerosol particles distributed between 10 and 1 μm; e) an aged sea salt input and f) SOA pinene. Each factor was also characterized by different composition in waters soluble compounds and different particles size distribution.

Sources of pollution and interrelationships between aerosol and precipitation chemistry at a central California site

This study examines co-located aerosol and precipitation chemistry data between 2010 and 2016 at Pinnacles National Monument ~65 km east of the coastline in central California. Positive matrix factorization analysis of the aerosol composition data revealed seven distinct pollutant sources: aged sea salt (25.7% of PM2.5), biomass burning (24.2% of PM2.5), fresh sea salt (15.0% of PM2.5), secondary sulfate (11.7% of PM2.5), dust (10.0% of PM2.5), vehicle emissions (8.2% of PM2.5), and secondary nitrate (5.2% of PM2.5). The influence of meteorology and transport on monthly patterns of PM2.5 composition is discussed. Only secondary sulfate exhibited a statistically significant change (a reduction) over time among the PM2.5 source factors. In contrast, PMcoarse exhibited a significant increase most likely due to dust influence. Monthly profiles of precipitation chemistry are summarized showing that the most abundant species in each month was either SO42−, NO3−, or Cl−. Intercomparisons between the precipitation and aerosol data revealed several features: (i) precipitation pH was inversely related to factors associated with more acidic aerosol constituents such as secondary sulfate and aged sea salt, in addition to being reduced by uptake of HNO3 in the liquid phase; (ii) two aerosol source factors (dust and aged sea salt) and PMcoarse exhibited a positive association with Ca2+ in precipitation, suggestive of directly emitted aerosol types with larger sizes promoting precipitation; and (iii) sulfate levels in both the aerosol and precipitation samples analyzed were significantly correlated with dust and aged sea salt PMF factors, pointing to the partitioning of secondary sulfate to dust and sea salt particles. The results of this work have implications for the region's air quality and hydrological cycle, in addition to demonstrating that the use of co-located aerosol and precipitation chemistry data can provide insights relevant to aerosol-precipitation interactions.

Associations of Source-apportioned Fine Particles with Cause-specific Mortality in California.

Exposure to ambient fine particulate matter (PM2.5) has been linked with premature mortality, but sources of PM2.5 have been less studied. We evaluated associations between source-specific PM2.5 exposures and cause-specific short-term mortality in eight California locations from 2002 to 2011. Speciated PM2.5 measurements were source-apportioned using Positive Matrix Factorization into eight sources and combined with death certificate data. We used time-stratified case-crossover analysis with conditional logistic regression by location and meta-analysis to calculate pooled estimates. Biomass burning was associated with all-cause mortality lagged 2 days after exposure (lag2) (% changelag2 in odds per interquartile range width increase in biomass burning PM2.5 = 0.8, 95% confidence interval [CI] = 0.2, 1.4), cardiovascular (% changelag2 = 1.3, 95% CI = 0.3, 2.4), and ischemic heart disease (% changelag2 = 2.0, 95% CI = 0.6, 3.5). Vehicular emissions were associated with increases in cardiovascular mortality (% changelag0 = 1.4, 95% CI = 0.0, 2.9). Several other sources exhibited positive associations as well. Many findings persisted during the cool season. Warm season biomass burning was associated with respiratory/thoracic cancer mortality (% changelag1 = 5.9, 95% CI = 0.7, 11.3), and warm season traffic was associated with all-cause (% changelag0 = 1.9, 95% CI = 0.1, 3.6) and cardiovascular (% changelag0 = 2.9, 95% CI = 0.1, 5.7) mortality. Our results suggest that acute exposures to biomass burning and vehicular emissions are linked with cardiovascular mortality, with additional sources (i.e., soil, secondary nitrate, secondary sulfate, aged sea salt, and chlorine sources) showing associations with other specific mortality types.

Baseline characterisation of source contributions to daily-integrated PM2.5 observations at Cape Grim using Radon-222

We discuss 15 years (2000–2015) of daily-integrated PM2.5 samples from the Cape Grim Station. Ion beam analysis and positive matrix factorisation are used to identify six source-type fingerprints: fresh sea salt (57%); secondary sulfate (14%); smoke (13%); aged sea salt (12%); soil dust (2.4%); and industrial metals (1.5%). An existing hourly radon-only baseline selection technique is modified for use with the daily-integrated observations. Results were not significantly different for days on which >20 hours were below the baseline radon threshold compared with days when all 24 hours satisfied the baseline criteria. This relaxed daily baseline criteria increased the number of samples for analysis by almost a factor of two. Two radon baseline thresholds were tested: historic (100 mBq m−3), and revised (50 mBq m−3). Median aerosol concentrations were similar for both radon thresholds, but maximum values were higher for the 100 mBq m−3 threshold. Back trajectories indicated more interaction with southern Australia and the Antarctic coastline for air masses selected with the 100 mBq m−3 threshold. Radon-only baseline selection using the 50 mBq m−3 threshold was more selective of minimal terrestrial influence than a similar recent study using wind direction and back trajectories. The ratio of concentrations between terrestrial and baseline days for the primary sources soil, smoke and industrial metals was 3.4, 2.6, and 5.5, respectively. Seasonal cycles of soil dust had a summer maximum and winter minimum. Seasonal cycles of smoke were of similar amplitude for terrestrial and baseline events, but of completely different shape: peaking in autumn and spring for terrestrial events, compared to summer for baseline conditions. Seasonal cycles of industrial metals had a summer maximum and winter minimum. A significant fraction of the Cape Grim baseline smoke and industrial metal contributions appeared to be derived from long-term transport (>3 weeks since last terrestrial influence).

Exploration of PM<sub>2.5</sub> sources on the regional scale in the Pearl River Delta based on ME-2 modeling

Abstract. The Pearl River Delta (PRD) of China, which has a population of more than 58 million people, is one of the largest agglomerations of cities in the world and had severe PM2.5 pollution at the beginning of this century. Due to the implementation of strong pollution control in recent decades, PM2.5 in the PRD has continuously decreased to relatively lower levels in China. To comprehensively understand the current PM2.5 sources in the PRD to support future air pollution control strategies in similar regions, we performed regional-scale PM2.5 field observations coupled with a state-of-the-art source apportionment model at six sites in four seasons in 2015. The regional annual average PM2.5 concentration based on the 4-month sampling was determined to be 37 µg m−3, which is still more than 3 times the WHO standard, with organic matter (36.9 %) and SO42- (23.6 %) as the most abundant species. A novel multilinear engine (ME-2) model was first applied to a comprehensive PM2.5 chemical dataset to perform source apportionment with predetermined constraints, producing more environmentally meaningful results compared to those obtained using traditional positive matrix factorization (PMF) modeling. The regional annual average PM2.5 source structure in the PRD was retrieved to be secondary sulfate (21 %), vehicle emissions (14 %), industrial emissions (13 %), secondary nitrate (11 %), biomass burning (11 %), secondary organic aerosol (SOA, 7 %), coal burning (6 %), fugitive dust (5 %), ship emissions (3 %) and aged sea salt (2 %). Analyzing the spatial distribution of PM2.5 sources under different weather conditions clearly identified the central PRD area as the key emission area for SO2, NOx, coal burning, biomass burning, industrial emissions and vehicle emissions. It was further estimated that under the polluted northerly air flow in winter, local emissions in the central PRD area accounted for approximately 45 % of the total PM2.5, with secondary nitrate and biomass burning being most abundant; in contrast, the regional transport from outside the PRD accounted for more than half of PM2.5, with secondary sulfate representing the most abundant transported species.

Estimation of the contributions of the sources driving PM2.5 levels in a Central Mediterranean coastal town

Receptor modelling techniques are widely used in order to identify the main natural and anthropogenic processes driving aerosol levels at a receptor. In this work, Positive Matrix Factorization (PMF) was used to apportion PM2.5 levels at a traffic site (Msida) located in a coastal town. 180 filters collected throughout a yearly sampling campaign conducted in 2016, were chemically characterized by light absorbance analysis, x-ray fluorescence and ion chromatography in order to determine the concentrations of black carbon, 17 elements and 5 ions, respectively. The resulting chemical data base was used in conjunction with PMF in order to identify the 7 components affecting the PM2.5 levels at the receptor site. Six of these sources are considered to be typical of the atmospheric composition of coastal traffic sites: traffic (27.3%), ammonium sulfate (23.6%), Saharan dust (15%), aged sea salt (12.7%), shipping (5%) and fresh sea salt (4.6%). This is the first time that such a study was carried out in Malta and helps in understanding the aerosol pollution climate of the Central Mediterranean, which is still relatively understudied when compared to the Eastern and Western Mediterranean. Furthermore, we have isolated a factor exclusive to Malta: the fireworks component, which is responsible for 2.9% of the PM2.5 and which has health implications due to its chemical composition. The results of this work should also serve to guide the policy makers in achieving the necessary emission reductions in order to achieve the WHO guideline for PM2.5 by 2020.

Eighteen-year trends of local and non-local impacts to ambient PM10 in Hong Kong based on chemical speciation and source apportionment

Along with rapid economic development in China in the past twenty years, air pollution has deteriorated significantly and then gradually improved afterwards. Emission changes in response to the economic development and control measures and their impacts to ambient pollution levels are thus of great scientific and policy-making implications. By using the eighteen-year PM10 speciation dataset that have been continuously collected at multiple stations over Hong Kong since 1998, we demonstrated a novel approach to identify long-term trends of local and non-local contributions to ambient PM10 in Hong Kong based on Positive Matrix Factorization source apportionment and backward trajectory cluster analysis. It is found that vehicle exhaust contribution had decreased from 9.9 μg·m−3 in 1998 to 3.4 μg·m−3 in 2015, corresponding to a 66% decrease. However, residual oil contribution increased threefold, which indicated ship emission needs to be primarily addressed in air pollution management in Hong Kong. The mostly non-local sources of secondary sulfate, industry, and coal / biomass burning all showed inverse V-shape trends during the eighteen years, indicating the dual roles of economic development and emission control in shaping the ambient pollution levels. Local contributions dominated for vehicle exhaust and aged sea salt, while non-local ones dominated for secondary sulfate, secondary nitrate, industry, and coal / biomass burning. Although with small fluctuations, non-local contributions consistently accounted for 63–70% of total PM10 during the eighteen years, similar as previous estimates using a different approach. Such a dominant non-local contribution highlights the importance of regional collaboration to reduce PM levels in Hong Kong.

Source apportionment of PM2.5 using positive matrix factorization (PMF) at a rural site in Korea

The sources of different pollutants contributing to ambient fine particles (PM2.5) on Daebu Island, Korea, were estimated. Twenty four hour integrated filter samples were collected from May 21–November 1, 2016, and analyzed for organic carbon, elemental carbon, ions, and trace elements. Positive matrix factorization was conducted on the PM2.5 chemical speciation data from the samples to define the pathways and sources of PM2.5 at the sampling site. A total of 80 samples and 24 chemical species were used to run the model and a total of nine sources were identified: secondary sulfate (29.0%), mobile (22.0%), secondary nitrate (13.2%), oil combustion (10.1%), coal combustion (9.4%), aged sea salt (7.9%), soil (5.6%), non-ferrous smelting (1.7%), and industrial activity (1.1%). Conditional probability and potential source contribution functions were then used to determine whether these sources were local or came from pollutants transported over long-range distances. The anthropogenic sources came from local emissions and originated from both industrialized and metropolitan areas, whereas the secondary inorganic aerosols were strongly influenced by the long-range transport of air pollutants from Shandong and Jiangsu provinces in China.

Chemical characterisation and source identification of atmospheric aerosols in the Snowy Mountains, south-eastern Australia

Characterisation of atmospheric aerosols is of major importance for: climate, the hydrological cycle, human health and policymaking, biogeochemical and palaeo-climatological studies. In this study, the chemical composition and source apportionment of PM2.5 (particulate matter with aerodynamic diameters less than 2.5μm) at Yarrangobilly, in the Snowy Mountains, SE Australia are examined and quantified. A new aerosol monitoring network was deployed in June 2013 and aerosol samples collected during the period July 2013 to July 2017 were analysed for 22 trace elements and black carbon by ion beam analysis techniques. Positive matrix factorisation and back trajectory analysis and trajectory clustering methods were employed for source apportionment and to isolate source areas and air mass travel pathways, respectively. This study identified the mean atmospheric PM2.5 mass concentration for the study period was (3.3±2.5)μgm−3. It is shown that automobile (44.9±0.8)%, secondary sulfate (21.4±0.9)%, smoke (12.3±0.6)%, soil (11.3±0.5)% and aged sea salt (10.1±0.4)% were the five PM2.5 source types, each with its own distinctive trends. The automobile and smoke sources were ascribed to a significant local influence from the road network and bushfire and hazard reduction burns, respectively. Long-range transport are the dominant sources for secondary sulfate from coal-fired power stations, windblown soil from the inland saline regions of the Lake Eyre and Murray-Darling Basins, and aged sea salt from the Southern Ocean to the remote alpine study site. The impact of recent climate change was recognised, as elevated smoke and windblown soil events correlated with drought and El Niño periods. Finally, the overall implications including potential aerosol derived proxies for interpreting palaeo-archives are discussed. To our knowledge, this is the first long-term detailed temporal and spatial characterisation of PM2.5 aerosols for the region and provides a crucial dataset for a range of multidisciplinary research.

Seasonal Source Apportionment of PM2.5 in Ningbo, a Coastal City in Southeast China

With the rapid economic development and urbanization of China, haze and photochemical smog events have been frequently observed during the last decade. To explore the temporal and spatial pollution characteristics in Ningbo, a medium-sized coastal city located in the Yangtze River Delta (YRD) in southeast China, 24-h PM2.5 (particulate matter with aerodynamic diameter ≤ 2.5 µm) samples were simultaneously collected at five sites (two urban residential sites, two urban coastal sites, and one suburban site) from winter 2012 to autumn 2013. The average PM2.5 concentration was 53.2 ± 30.4 µg m–3. Furthermore, the concentration exhibited a seasonal variation: It was highest in winter and lowest in summer. The urban residential sites had the highest PM2.5 concentrations, followed by the urban coastal sites, and the suburban site had the lowest concentration. OM (Organic Matters) and secondary inorganic ions (sulfate, nitrate, and ammonium) were the dominant components of the PM2.5. As a coastal city with industrial zones, sources are more complex in Ningbo than in inland cities due to ship emissions and the interactions between land and sea, and the marine and atmospheric environments. Positive matrix factorization (PMF) was used to apportion the particle sources. Nine factors were resolved in this study: secondary nitrate, vehicle exhaust, secondary sulfate, coal combustion, industrial emission, ship emission, dust, biomass burning, and aged sea salt, with average contributions of 26%, 21%, 13%, 12%, 9%, 7%, 5%, 4%, and 3%, respectively. Secondary nitrate and vehicle exhaust were the major sources of PM2.5 pollution in Ningbo. Coal combustion contributed significantly in winter and autumn, whereas sea salt formed a considerable contribution in summer. This study suggests that decreasing the PM2.5 pollution in Ningbo requires not only strategies for reducing local primary sources but also joint inter-regional prevention and the control of air pollution in the YRD.

Background PM2.5 source apportionment in the remote Northwestern United States

This study used the Environmental Protection Agency's positive matrix factorization model (EPA PMF5.0) to identify five primary source factors contributing to the ambient PM2.5 concentrations at Cheeka Peak Atmospheric Observatory (CPO), Neah Bay WA between January 2011 and December 2014. CPO is home to both an IMPROVE (Interagency Monitoring for Protected Visual Environments) and a NCore multi-pollutant monitoring site. Chemically resolved particulate data from the IMPROVE site was the input data to EPA PMF5.0 and the resulting source factors were derived solely from these data. Solutions from the model were analyzed in context with trace gas and meteorological data collected at the NCore site located roughly 10 m away. Seasonal and long-term trends were analyzed for all five factors and provide the first complete source apportionment analysis of PM2.5 at this remote location. The first factor, identified as marine-traffic residual fuel oil (RFO), was the highest contributor to PM2.5 during late summer. Over the 4-year analysis, the RFO percent contribution to total PM2.5 declined. This is consistent with previous studies and may be attributed to regulations restricting the sulfur content of ship fuel. Biomass combustion emissions (BMC) and sea salt were the largest PM2.5 sources observed at CPO in winter, accounting for over 80% of the fine particulate. BMC accounted for a large percent of the fine particulate pollution when winds were easterly, or continental. Sea salt was the dominant winter factor when winds blew from the west. Measured trace carbon monoxide (CO) and reactive nitrogen species (NOy) were most strongly correlated with the BMC factor and continental winds. The fourth factor was identified as aged crustal material, or dust. In all three years, dust peaked in the spring and was associated exclusively with north-easterly winds. The last factor was identified as aged sea salt mixed with nitrate, sulfate, and other components common to RFO and BMC source factors. It did not exhibit a strong seasonal cycle or dependence on wind direction.

Long term fine aerosols at the Cape Grim global baseline station: 1998 to 2016

Abstract: Fine aerosol measurements have been undertaken at the Cape Grim global baseline station since 1992. Ion beam analysis techniques were then used to determine the elemental composition of the samples from which source fingerprints can be determined. In this study six source fingerprints were identified to contribute to the measurements of PM 2.5 at Cape Grim (from 1998 to 2016); fresh sea salt (57%), secondary sulfate and nitrates (14%), smoke (13%), aged sea salt (the product of NaCl reactions with SO 2 ; 12%), soil dust (2.4%) and industrial metals (1.5%). Back trajectory analysis showed that local Tasmanian sources of soil dust contributed to the high soil dust measurements. High measurements of secondary aerosols were recorded when air masses were arriving from the Australian mainland, in the direction of the Victorian power stations. When air masses were arriving from the baseline sector, the maximum concentration of aged sea salt was 1.3 μg/m 3 , compared to overall maximum of 4.9 μg/m 3 . For secondary sulfates and nitrates the maximum concentrations were 2.5 and 7.5 μg/m 3 from the baseline sector and overall, respectively. While measurements at Cape Grim can be affected from long range transport from mainland Australia and some local Tasmanian sources, the average concentrations of anthropogenic sources are still considerably lower than those measured at more populated areas. For example, at Lucas Heights (located south-west of the Sydney central business district, with little local sources) the average concentrations of secondary sulfates/nitrates and aged sea air were 1.4 and 1.0 μg/m 3 , respectively; compared to average concentrations of 0.8 and 0.6 μg/m 3 , at Cape Grim. The average concentrations of smoke were compatible at the two sites. The impact of primary aerosols from vehicle exhaust at Cape Grim was limited and no corresponding fingerprint was resolved.

Optical, physical and chemical properties of aerosols transported to a coastal site in the western Mediterranean: a focus on primary marine aerosols

Abstract. As part of the ChArMEx-ADRIMED campaign (summer 2013), ground-based in situ observations were conducted at the Ersa site (northern tip of Corsica; 533 m a.s.l.) to characterise the optical, physical and chemical properties of aerosols. During the observation period, a major influence of primary marine aerosols was detected (22–26 June), with a mass concentration reaching up to 6.5 µg m−3 and representing more than 40 % of the total PM10 mass concentration. Its relatively low ratio of chloride to sodium (average of 0.57) indicates a fairly aged sea salt aerosol at Ersa. In this work, an original data set, obtained from online real-time instruments (ATOFMS, PILS-IC) has been used to characterise the ageing of primary marine aerosols (PMAs). During this PMA period, the mixing of fresh and aged PMAs was found to originate from both local and regional (Gulf of Lion) emissions, according to local wind measurements and FLEXPART back trajectories. Two different aerosol regimes have been identified: a dust outbreak (dust) originating from Algeria/Tunisia, and a pollution period with aerosols originating from eastern Europe, which includes anthropogenic and biomass burning sources (BBP). The optical, physical and chemical properties of the observed aerosols, as well as their local shortwave (SW) direct radiative effect (DRE) in clear-sky conditions, are compared for these three periods in order to assess the importance of the direct radiative impact of PMAs compared to other sources above the western Mediterranean Basin. As expected, AERONET retrievals indicate a relatively low local SW DRF during the PMA period with mean values of −11 ± 4 at the surface and −8 ± 3 W m−2 at the top of the atmosphere (TOA). In comparison, our results indicate that the dust outbreak observed at our site during the campaign, although of moderate intensity (AOD of 0.3–0.4 at 440 nm and column-integrated SSA of 0.90–0.95), induced a local instantaneous SW DRF that is nearly 3 times the effect calculated during the PMA period, with maximum values up to −40 W m−2 at the surface. A similar range of values were found for the BBP period to those during the dust period (SW DRF at the surface and TOA of −23 ± 6 and −15 ± 4 W m−2 respectively). The multiple sources of measurements at Ersa allowed the detection of a PMA-dominant period and their characterisation in terms of ageing, origin, transport, optical and physical properties and direct climatic impact.

Particulate matter from re-suspended mineral dust and emergency cause-specific respiratory hospitalizations in Hong Kong

While contribution from non-exhaust particulate matter (PM) emissions towards traffic-related emissions is increasing, few epidemiologic evidence of their health impact is available. We examined the association of short-term exposure to PM10 apportioned to re-suspended mineral dust with emergency hospitalizations for three major respiratory causes in Hong Kong between 2001 and 2008. Time-series regression model was constructed to examine association of PM10 from re-suspended mineral dust with emergency hospitalizations for upper respiratory infection (URI), chronic obstructive pulmonary disease (COPD) and asthma at exposure lag 0–5 days, adjusting for time trends, seasonality, temperature and relative humidity. An interquartile range (6.8 μg/m3) increment in re-suspended mineral dust on previous day was associated with 0.66% (95% CI: 0.12, 0.98) increase in total respiratory hospitalizations, and 1.01% (95% CI: 0.14, 1.88) increase in URI hospitalizations. A significant 0.66%–0.80% increases in risk of COPD hospitalizations were found after exposure to re-suspended mineral dust at lag 3 or later. Exposure to mineral dust at lag 4 was linked to 1.71% increase (95% CI: 0.14, 2.22) in asthma hospitalizations. Associations from single-pollutant models remained significant in multi-pollutant models, which additionally adjusted for PM10 contributing from vehicle exhaust, regional combustion, residual oil, fresh sea salt, aged sea salt, secondary nitrate and secondary sulfate, or gaseous pollutants (i.e., nitrogen dioxide, sulfur dioxide, or ozone), respectively. Our findings provide insight into the biological mechanism by which non-exhaust pollution may be associated with risk of adverse respiratory outcomes, and also stress the needs for strategies to reduce emission and re-suspension of mineral dust. More research is warranted to assess the health effects of different non-exhaust PM emissions under various roadway conditions and vehicle fleets.

Sources and mixing state of summertime background aerosol in the north-western Mediterranean basin

Abstract. An aerosol time-of-flight mass spectrometer (ATOFMS) was employed to provide real-time single particle mixing state and thereby source information for aerosols impacting the western Mediterranean basin during the ChArMEx-ADRIMED and SAF-MED campaigns in summer 2013. The ATOFMS measurements were made at a ground-based remote site on the northern tip of Corsica. Twenty-seven distinct ATOFMS particle classes were identified and subsequently grouped into eight general categories: EC-rich (elemental carbon), K-rich, Na-rich, amines, OC-rich (organic carbon), V-rich, Fe-rich and Ca-rich particles. Mass concentrations were reconstructed for the ATOFMS particle classes and found to be in good agreement with other co-located quantitative measurements (PM1, black carbon (BC), organic carbon, sulfate mass and ammonium mass). Total ATOFMS reconstructed mass (PM2. 5) accounted for 70–90 % of measured PM10 mass and was comprised of regionally transported fossil fuel (EC-rich) and biomass burning (K-rich) particles. The accumulation of these transported particles was favoured by repeated and extended periods of air mass stagnation over the western Mediterranean during the sampling campaigns. The single particle mass spectra proved to be valuable source markers, allowing the identification of fossil fuel and biomass burning combustion sources, and was therefore highly complementary to quantitative measurements made by Particle into Liquid Sampler ion chromatography (PILS-IC) and an aerosol chemical speciation monitor (ACSM), which have demonstrated that PM1 and PM10 were comprised predominantly of sulfate, ammonium and OC. Good temporal agreement was observed between ATOFMS EC-rich and K-rich particle mass concentrations and combined mass concentrations of BC, sulfate, ammonium and low volatility oxygenated organic aerosol (LV-OOA). This combined information suggests that combustion of fossil fuels and biomass produced primary EC- and OC-containing particles, which then accumulated ammonium, sulfate and alkylamines during regional transport. Three other sources were also identified: local biomass burning, marine and shipping. Local combustion particles (emitted in Corsica) contributed little to PM2. 5 particle number and mass concentrations but were easily distinguished from regional combustion particles. Marine emissions comprised fresh and aged sea salt: the former was detected mostly during a 5-day event during which it accounted for 50–80 % of sea salt aerosol mass, while the latter was detected throughout the sampling period. Dust was not efficiently detected by the ATOFMS, and support measurements showed that it was mainly in the PM2. 5–10 fraction. Shipping particles, identified using markers for heavy fuel oil combustion, were associated with regional emissions and represented only a small fraction of PM2. 5 particle number and mass concentration at the site.

Ice cloud formation potential by free tropospheric particles from long‐range transport over the Northern Atlantic Ocean

AbstractLong‐range transported free tropospheric particles can play a significant role on heterogeneous ice nucleation. Using optical and electron microscopy we examine the physicochemical characteristics of ice nucleating particles (INPs). Particles were collected on substrates from the free troposphere at the remote Pico Mountain Observatory in the Azores Islands, after long‐range transport and aging over the Atlantic Ocean. We investigate four specific events to study the ice formation potential by the collected particles with different ages and transport patterns. We use single‐particle analysis, as well as bulk analysis to characterize particle populations. Both analyses show substantial differences in particle composition between samples from the four events; in addition, single‐particle microscopy analysis indicates that most particles are coated by organic material. The identified INPs contained mixtures of dust, aged sea salt and soot, and organic material acquired either at the source or during transport. The temperature and relative humidity (RH) at which ice formed, varied only by 5% between samples, despite differences in particle composition, sources, and transport patterns. We hypothesize that this small variation in the onset RH may be due to the coating material on the particles. This study underscores and motivates the need to further investigate how long‐range transported and atmospherically aged free tropospheric particles impact ice cloud formation.

Identification of Sources of Fine Particulate Matter in Kandy, Sri Lanka

ABSTRACTKandy is the second largest city in Sri Lanka and a major tourist destination. It is a fast growing city with continuous construction of buildings, roads and historical places. More than 100 samples of fine particulate matter (PM) were collected using a GENT stacked filter sampler from a fixed site at the regional sampling station of Department of Meteorology situated in Katugastota, Kandy over the period of 2012 to 2014. Black carbon (BC) in these filters were determined by reflectance measurements while their elemental compositions were determined using the X-ray fluorescence spectrometry. Analysis of the elemental data suggests that the PM in Kandy originates largely from re-suspended soil and anthropogenic sources. The fine particulate matter data including BC and major elements (Na, Mg, Al, Si, Cl, Fe, Zn, Ni, Cu, V, S, Br, Pb, Cr, K, Ca and Ti) was analyzed using EPA-PMF version 5.0 (Positive Matrix Factorization) to explore the possible sources of the PM at the study site. Five factors were found and identified as soil, aged sea salt, vehicular emissions, biomass burning, and industrial sources.

Comprehensive assessment of PM2.5 physicochemical properties during the Southeast Asia dry season (southwest monsoon)

AbstractA comprehensive assessment of fine particulate matter (PM2.5) compositions during the Southeast Asia dry season is presented. Samples of PM2.5 were collected between 24 June and 14 September 2014 using a high‐volume sampler. Water‐soluble ions, trace species, rare earth elements, and a range of elemental carbon (EC) and organic carbon were analyzed. The characterization and source apportionment of PM2.5 were investigated. The results showed that the 24 h PM2.5 concentration ranged from 6.64 to 68.2 µg m−3. Meteorological driving factors strongly governed the diurnal concentration of aerosol, while the traffic in the morning and evening rush hours coincided with higher levels of CO and NO2. The correlation analysis for non sea‐salt K+‐EC showed that EC is potentially associated with biomass burning events, while the formation of secondary organic carbon had a moderate association with motor vehicle emissions. Positive matrix factorization (PMF) version 5.0 identified the sources of PM2.5: (i) biomass burning coupled with sea salt [I] (7%), (ii) aged sea salt and mixed industrial emissions (5%), (iii) road dust and fuel oil combustion (7%), (iv) coal‐fired combustion (25%), (v) mineral dust (8%), (vi) secondary inorganic aerosol (SIA) coupled with F− (15%), and (vii) motor vehicle emissions coupled with sea salt [II] (24%). Motor vehicle emissions, SIA, and coal‐fired power plant are the predominant sources contributing to PM2.5. The response of the potential source contribution function and Hybrid Single‐Particle Lagrangian Integrated Trajectory backward trajectory model suggest that the outline of source regions were consistent to the sources by PMF 5.0.

Source apportionment of PM2.5 chemically speciated mass and particle number concentrations in New York City

The major sources of fine particulate matter (PM2.5) in New York City (NYC) were apportioned by applying positive matrix factorization (PMF) to two different sets of particle characteristics: mass concentrations using chemical speciation data and particle number concentrations (PNC) using number size distribution, continuously monitored gases, and PM2.5 data. Post-processing was applied to the PMF results to: (i) match with meteorological data, (ii) use wind data to detect the likely locations of the local sources, and (iii) use concentration weighted trajectory models to assess the strength of potential regional/transboundary sources. Nine sources of PM2.5 mass were apportioned and identified as: secondary ammonium sulfate, secondary ammonium nitrate, road traffic exhaust, crustal dust, fresh sea-salt, aged sea-salt, biomass burning, residual oil/domestic heating and zinc. The sources of PNC were investigated using hourly average number concentrations in six size bins, gaseous air pollutants, mass concentrations of PM2.5, particulate sulfate, OC, and EC. These data were divided into 3 periods indicative of different seasonal conditions. Five sources were resolved for each period: secondary particles, road traffic, NYC background pollution (traffic and oil heating largely in Manhattan), nucleation and O3-rich aerosol. Although traffic does not account for large amounts of PM2.5 mass, it was the main source of particles advected from heavily trafficked zones. The use of residual oil had limited impacts on PM2.5 mass but dominates PNC in cold periods.

Insights into different nitrate formation mechanisms from seasonal variations of secondary inorganic aerosols in Shanghai

The dominant mechanisms for the formation of fine particulate nitrate during four seasons were proposed by evaluating the correlations between [NO3−]/[SO42−] and [NH4+]/[SO42−]. Size-resolved aerosols were collected in Shanghai from April 2013 to January 2014. The concentration of fine particulate nitrate was below one tenth of the concentration of sulfate in summer, whereas fine particulate nitrate dominated over sulfate in winter. Influenced by aged sea salt aerosols, the molar ratio of [Na+]/[NH4+] reached 53 ± 49% and the depletion of chloride was very significant (0.83) during autumn. In spring, the increase of nitrate concentration became evident for [NH4+]/[SO42−]>2, indicating that sulfate is fully neutralized. During summertime, nighttime hydrolysis of N2O5 dominated the fine particulate nitrate formation. The thresholds of [NH4+]/[SO42−] for nitrate formation in autumn and winter were wrongly characterized by the linear regression between [NO3−]/[SO42−] and [NH4+]/[SO42−], because considerable amounts of Na2SO4 and NH4Cl were present. Replaced by free ammonium in the function equation, it was established that the winter and spring aerosols shared the same nitrate formation mechanism. On the basis of free sulfate, it was evident that both homogeneous neutralization and hydrolysis of N2O5 mechanisms were involved during autumn.