Size-resolved sulfate and ammonium measurements in marine boundary layer over the North and South Pacific

Marine background levels of non-sea-salt- (nss-) SO₄²⁻ (5.0–9.7 neq m⁻³), NH₄⁺ (2.1–4.4 neq m⁻³) and elemental carbon (EC) (40–80 ngC m⁻³) in aerosol samples were measured over the equatorial and South Pacific during a cruise by the R/V Hakuho-maru from November 2001 to March 2002. High concentrations of nss-SO₄²⁻ (47–94 neq m⁻³), NH₄⁺ (35–94 neq m⁻³) and EC (130–460 ngC m⁻³) were found in the western North Pacific near the coast of the Asian continent under the influence of the Asian winter monsoon. Particle size distributions of ionic components showed that the equivalent concentrations of nss-SO₄²⁻ were balanced with those of NH₄⁺ in the size range of 0.06<D<0.22 μm, whereas the concentration ratios of NH₄⁺ to nss-SO₄²⁻ in the size range of D>0.22 μm were decreased with increase in particle size. We estimated the source contributions of those aerosol components in the marine background air over the equatorial and South Pacific. Biomass burning accounted for the large fraction (80–98% in weight) of EC and the minor fraction (2–4% in weight) of nss-SO₄²⁻. Marine biogenic source accounted for several tens percents of NH₄⁺ and nss-SO₄²⁻. In the accumulation mode, 70% of particle number existed in the size range of 0.1<D<0.2 μm. In the size rage of 0.06<D<0.22 μm, the dominant aerosol component of (NH₄)₂SO₄ would be mainly derived from the marine biogenic sources.     

The impact of transpacific transport of mineral dust in the United States

We use a global chemical transport model (GEOS-Chem) to estimate the impact of transpacific transport of mineral dust on aerosol concentrations in North America during 2001. We have implemented two dust mobilization schemes in the model (GOCART and DEAD) and find that the best simulation of North American surface observations with GEOS-Chem is achieved by combining the topographic source used in GOCART with the entrainment scheme used in DEAD. This combination restricts dust emissions to year-round arid areas but includes a significant wind threshold for dust mobilization. The model captures the magnitude and seasonal cycle of observed surface dust concentrations over the northern Pacific. It simulates the free tropospheric outflow of dust from Asia observed in the TRACE-P and ACE-Asia aircraft campaigns of spring 2001. It reproduces the timing and distribution of Asian dust outbreaks in North America during April–May. Beyond these outbreaks we find persistent Asian fine dust (averaging 1.2 μg m⁻³) in surface air over the western United States in spring, with much weaker influence (0.25 μg m⁻³) in summer and fall. Asian influence over the eastern United States is 30–50% lower. We find that transpacific sources accounted for 41% of the worst dust days in the western United States in 2001.     

Biogenic emission of dimethylsulfide (DMS) from the North Yellow Sea,China and its contribution to sulfate in aerosol during summer

Seawater, atmospheric dimethylsulfide (DMS) and aerosol compounds, potentially linked with DMS oxidation, such as methanesulfonic acid (MSA) and non-sea-salt sulfate (nss-SO₄^2?) were determined in the North Yellow Sea, China during July–August, 2006. The concentrations of seawater and atmospheric DMS ranged from 2.01 to 11.79 nmol l^?1 and from 1.68 to 8.26 nmol m^?3, with average values of 6.20 nmol l^?1 and 5.01 nmol m^?3, respectively. Owing to the appreciable concentration gradient, DMS accumulated in the surface water was transferred into the atmosphere, leading to a net sea-to-air flux of 6.87 μmol m^?2 d^?1 during summer. In the surface seawater, high DMS values corresponded well with the concurrent increases in chlorophyll a levels and a significant correlation was observed between integrated DMS and chlorophyll a concentrations. In addition, the concentrations of MSA and nss-SO₄^2? measured in the aerosol samples ranged from 0.012 to 0.079 μg m^?3 and from 3.82 to 11.72 μg m^?3, with average values of 0.039 and 7.40 μg m^?3, respectively. Based on the observed MSA, nss-SO₄^2? and their ratio, the relative biogenic sulfur contribution was estimated to range from 1.2% to 11.5%, implying the major contribution of anthropogenic source to sulfur budget in the study area.     

An analysis of seasonal surface dust aerosol concentrations in the western US (2001–2004): Observations and model predictions

Long-term surface observations indicate that soil dust represents over 30% of the annual fine (particle diameter less than 2.5 μm) particulate mass in many areas of the western US; in spring and summer, it represents an even larger fraction. There are numerous dust-producing playas in the western US, but surface dust aerosol concentrations in this region are also influenced by dust of Asian origin. This study examines the seasonality of surface soil dust concentrations at 15 western US sites using observations from the Interagency Monitoring of PROtected Visual Environments (IMPROVE) network from 2001 to 2004. Average soil concentrations in particulate matter less than 10 μm in diameter (PM₁₀) were lowest in winter and peaked during the summer months at these sites; however, episodic higher-concentration events (>10 μg m⁻³) occurred in the spring, the time of maximum Asian dust transport to the western US. Simulated surface dust concentrations from the Navy Aerosol Analysis and Prediction System (NAAPS) suggested that long-range transport from Asia dominates surface dust concentrations in the western US in the spring, and that, although some long-range transport does occur throughout the year (1–2 μg m⁻³), locally generated dust plays a larger role in the region in summer and fall. However, NAAPS simulated some anomalously high concentrations (>50 μg m⁻³) of local dust in the fall and winter months over portions of the western US. Differences between modeled and observed dust concentrations were attributed to overestimation of total observed soil dust concentrations by the assumptions used to convert IMPROVE measurements into PM₁₀ soil concentrations, lack of inhibition of model dust production in snow-covered regions, and lack of seasonal agricultural sources in the model.     

The continuous field measurements of soluble aerosol compositions at the Taipei Aerosol Supersite,Taiwan

The characteristics of ambient aerosols, affected by solar radiation, relative humidity, wind speed, wind direction, and gas–aerosol interaction, changed rapidly at different spatial and temporal scales. In Taipei Basin, dense traffic emissions and sufficient solar radiation for typical summer days favored the formation of secondary aerosols. In winter, the air quality in Taipei Basin was usually affected by the Asian continental outflows due to the long-range transport of pollutants carried by the winter monsoon. The conventional filter-based method needs a long time for collecting aerosols and analyzing compositions, which cannot provide high time-resolution data to investigate aerosol sources, atmospheric transformation processes, and health effects. In this work, the in situ ion chromatograph (IC) system was developed to provide 15-min time-resolution data of nine soluble inorganic species (Cl⁻, NO₂⁻, NO₃⁻, SO₄²⁻, Na⁺, NH₄⁺, K⁺, Mg²⁺ and Ca²⁺). Over 89% of all particles larger than approximately 0.056 μm were collected by the in situ IC system. The in situ IC system is estimated to have a limit of detection lower than 0.3 μg m⁻³ for the various ambient ionic components. Depending on the hourly measurements, the pollutant events with high aerosol concentrations in Taipei Basin were associated with the local traffic emission in rush hour, the accumulation of pollutants in the stagnant atmosphere, the emission of industrial pollutants from the nearby factories, the photochemical secondary aerosol formation, and the long-range transport of pollutants from Asian outflows.     

Transport of SO2 and aerosol over the Yellow sea

Aircraft measurements of air pollutants were made to investigate the characteristic features of long-range transport of sulfur compounds over the Yellow Sea for the periods of 26–27 April and 7–10 November in 1998, and 9–11 April and 19 June in 1999, together with aerosol measurements at the Taean background station in Korea. The overall mean concentrations of SO₂, O₃ and aerosol number in the boundary layer for the observation period ranged 0.1–7.4 ppb 32.1–64.1 ppb and 1.0–143.6 cm⁻³, respectively. It was found that the air mass over the Yellow Sea had a character of both the polluted continental air and clean background air, and the sulfur transport was mainly confined in the atmospheric boundary layer. The median of SO₂ concentration within the boundary layer was about 0.1–2.2 ppb. However, on 8 November, 1998, the mean concentrations of SO₂ and aerosol number increased up to 7.4 ppb and 109.5 cm⁻³, respectively, in the boundary layer, whereas O₃ concentration decreased remarkably. This enhanced SO₂ concentration occurred in low level westerly air stream from China to Korea. Aerosol analyses at the downstream site of Taean in Korea showed 2–3 times higher sulfate concentration than that of other sampling days, indicating a significant amount of SO₂ conversion to non sea-salt sulfate during the long-range transport.     

Seasonal and spatial trends in the sources of fine particle organic carbon in Israel,Jordan, and Palestine

A study of carbonaceous particulate matter (PM) was conducted in the Middle East at sites in Israel, Jordan, and Palestine. The sources and seasonal variation of organic carbon, as well as the contribution to fine aerosol (PM_2.5) mass, were determined. Of the 11 sites studied, Nablus had the highest contribution of organic carbon (OC), 29%, and elemental carbon (EC), 19%, to total PM_2.5 mass. The lowest concentrations of PM_2.5 mass, OC, and EC were measured at southern desert sites, located in Aqaba, Eilat, and Rachma. The OC contribution to PM_2.5 mass at these sites ranged between 9.4% and 16%, with mean annual PM_2.5 mass concentrations ranging from 21 to 25 ug m^?3. These sites were also observed to have the highest OC to EC ratios (4.1–5.0), indicative of smaller contributions from primary combustion sources and/or a higher contribution of secondary organic aerosol. Biomass burning and vehicular emissions were found to be important sources of carbonaceous PM in this region at the non-southern desert sites, which together accounted for 30%–55% of the fine particle organic carbon at these sites. The fraction of measured OC unapportioned to primary sources (1.4 μgC m^?3 to 4.9 μgC m^?3; 30%–74%), which has been shown to be largely from secondary organic aerosol, is relatively constant at the sites examined in this study. This suggests that secondary organic aerosol is important in the Middle East during all seasons of the year.     

Multi-year hourly PM2.5 carbon measurements in New York: Diurnal,day of week and seasonal patterns

Multi-year hourly measurements of PM_2.5 elemental carbon (EC) and organic carbon (OC) from a site in the South Bronx, New York were used to examine diurnal, day of week and seasonal patterns. The hourly carbon measurements also provided temporally resolved information on sporadic EC spikes observed predominantly in winter. Furthermore, hourly EC and OC data were used to provide information on secondary organic aerosol formation. Average monthly EC concentrations ranged from 0.5 to 1.4 μg m^?3 with peak hourly values of several μg m^?3 typically observed from November to March. Mean EC concentrations were lower on weekends (approximately 27% lower on Saturday and 38% lower on Sunday) than on weekdays (Monday to Friday). The weekday/weekend difference was more pronounced during summer months and less noticeable during winter. Throughout the year EC exhibited a similar diurnal pattern to NO_x showing a pronounced peak during the morning commute period (7–10 AM EST). These patterns suggest that EC was impacted by local mobile emissions and in addition by emissions from space heating sources during winter months. Although EC was highly correlated with black carbon (BC) there was a pronounced seasonal BC/EC gradient with summer BC concentrations approximately a factor of 2 higher than EC. Average monthly OC concentrations ranged from 1.0 to 4.1 μg m^?3 with maximum hourly concentrations of 7–11 μg m^?3 predominantly in summer or winter months. OC concentrations generally correlated with PM_2.5 total mass and aerosol sulfate and with NO_x during winter months. OC showed no particular day of week pattern. The OC diurnal pattern was typically different than EC except in winter when OC tracked EC and NO_x indicating local primary emissions contributed significantly to OC during winter at the urban location. On average secondary organic aerosol was estimated to account for 40–50% of OC during winter and up to 63–73% during summer months.     

A Lagrangian model investigation of chemico-microphysical evolution of northeast Asian pollution plumes within the MBL during TRACE-P

In this work, we determine the major channels through which air pollutants, mainly originating in Northeast Asian mega-cities, flow out into the Northwestern Pacific atmosphere. For this purpose, comprehensive backward/forward trajectory analyses are conducted. Two important channels along which pollutants from the Northeast Asian mega-cities flow out are defined, and are labeled as “DC8 transport path” and “P3B transport path”. We then comprehensively examine the chemico-microphysical transformations of the anthropogenic pollutants from the Northeast Asian mega-cities along the two major transport paths, using a new Lagrangian forward-trajectory photochemical model. In the newly developed model, state-of-the-science parameterizations for considering chemico-microphysical aging processes and atmospheric aerosol processes are incorporated. As air masses travel toward low latitudes through the marine boundary layer (MBL), the temperature increases along the trajectories and large amounts of PAN experience thermal decomposition. By this process, PAN can be an important supplier of NO₂ in the remote MBL. The O₃ productions in the remote Northwestern Pacific MBL are fueled and maintained by NO_x provided from the PAN decomposition. High O₃ levels (>50 ppb) are observed within the remote MBL of the Northwestern Pacific Oceans from several TRACE-P DC8 and P3B measurements under the continental outflow situations. Gas-phase SO₂ is continuously converted into nss-sulfate via heterogeneous oxidation reaction with H₂O₂ at a particle pH of 2–5. The Lagrangian-trajectory modeling studies also indicate that in the remote MBL of Northwestern Pacific Ocean under continental outflow situations, conditions are unfavorable for nucleation events, because of the depletion of SO₂, the large aerosol surface areas available for H₂SO₄ sink, and high temperatures.     

Annual and seasonal trends in chemical composition of precipitation in Japan during 1989–1998

Annual and seasonal trends were discussed for precipitation chemistry in Japan on the basis of a nationwide monitoring network by Japan Environment Agency. For this analysis, 17 sites, selected from the 23 network sites after evaluation of data completeness for the present purpose, were grouped into four areas in terms of the sea which could characterize each area: the Pacific Ocean, the Japan Sea, the Seto Inland Sea and the East China Sea areas. Major ion concentrations at each site were subjected to least-squares multiple regression analysis, and discussion was principally focused on the area-groups. Each area showed significant (p<0.05) decreasing trends in non-sea-salt sulfate (nss-SO₄²⁻) concentrations with the annual mean change rate of −3.0% yr⁻¹, whereas no significant trends were detected for NO₃⁻ at 59% of the sites. Ammonium (NH₄⁺) showed significant increasing trends for 35%, and decreasing trends for 18% of the sites; and, the maximum change rate of 3.8% yr⁻¹ was recorded in the Pacific Ocean area. Non-sea-salt calcium (nss-Ca²⁺) concentrations significantly decreased in northern and some industrialized areas. Both the annual cycle-amplitudes and effects of precipitation amounts were significant for the four ions at almost all sites. The maximum concentrations of nss-SO₄²⁻ and -Ca²⁺ occurred from winter to spring at most sites. The seasons when the maximum concentrations of NO₃⁻ and NH₄⁺ occurred, were found to differ from area to area. Furthermore, the trends in precipitation nss-SO₄²⁻, and NO₃⁻ were qualitatively consistent with those of anthropogenic emissions of SO₂, and NO_x in Japan, respectively.     

Southeastward transport of Asian dust: Source,transport and its contributions to Taiwan

Atmospheric Aluminum measured in northern Taiwan from 2003 to 2006 is used as a dust tracer, from which dust concentrations are derived, and major Asian dust events are determined. The source locations for the major dust events are traced back and identified, and the processes leading to the southeastward transport of Asian dust is investigated. The derived dust concentrations are compared to the local PM₁₀ (particle with size less than 10 μm) concentrations, and the impacts of Asian dust on the air quality of Taiwan are quantified.According to the backward trajectory and dust observation analyses, most of the southeastward transport of major Asian dust events originate from Mongolia and Inner Mongolia in northern China, and only one out of 16 events is generated from western China. Modeling studies and weather analyses of dust events suggest that the southeastward transport of Asian dust is usually generated behind a surface front and transported downwind behind the associated upper level trough. The associated upper level trough is usually deep, in which the northwesterly wind behind the trough favors the southeastward transport of dust to lower latitudes. Dust transported to Taipei generally occur during periods of large-scale subsidence.Asian dust contributes about 15 μg m^?3 of aerosol particles to northern Taiwan during winter monsoon, which accounts for about 24–30% of the PM₁₀ concentrations to the northern Taiwan. The contributions of Asian dust are raised pronouncedly to about 60–70% during major dust events. The impacts of Asian dust on Taiwan's air quality are most substantial in December. The Asian dust impacts decrease in other months, but still remain at around 30% in the late winter to early spring.     

Observations and modelling of aerosol growth in marine stratocumulus—case study

Airborne measurements of the growth of the marine accumulation mode after multiple cycles through stratocumulus cloud are presented. The nss-sulphate cloud residual mode was log-normal in spectral shape and it’s mode radius was observed to progressively increase in size from 0.78 to 0.94 μm over 155 min of air parcel evolution through the cloudy marine boundary layer. The primary reason for this observed growth was thought to result from aqueous phase oxidation of SO₂ to aerosol sulphate in activated cloud drops. An aqueous phase aerosol–cloud-chemistry model was used to simulate this case study of aerosol growth and was able to closely reproduce the observed growth. The model simulations illustrate that aqueous phase oxidation of SO₂ in cloud droplets was able to provide enough additional sulphate mass to increase the size of activated aerosol. During a typical cloud cycle simulation, ≈4.6 nmoles kg^-1_air (0.44 μg m^-3) of sulphate mass was produced with ≈70% of sulphate production occurring in cloud droplets activated upon sea-salt nuclei and ≈30% occurring upon nss-sulphate nuclei, even though sea-salt nuclei contributed less than 15% to the activated droplet population. The high fraction of nss-sulphate mass internally mixed with sea-salt aerosol suggests that aqueous phase oxidation of SO₂ in cloud droplets activated upon sea-salt nuclei is the dominant nss-sulphate formation mechanism and that sea-salt aerosol provides the primary chemical sink for SO₂ in the cloudy marine boundary layer.     

Direct measurements and parameterisation of aerosol flux,concentration and emission velocity above a city

Articles have recently been published on aerosol size distributions and number concentrations in cities, however there have been no studies on transport of these particles. Eddy covariance measurements of vertical transport of aerosol in the size range 11 nm<D_p<3 μm are presented here. The analysis shows that typical average aerosol number fluxes in this size range vary between 9000 and 90,000 cm⁻² s⁻¹. With concentrations between 3000 and 20,000 cm⁻³ this leads to estimates of particle emission velocity between 20 and 75 mm s⁻¹. The relationships between number flux and traffic activity, along with emission velocity and boundary layer stability are demonstrated and parameterised. These are used to derive an empirical parameterisation for aerosol concentration in terms of traffic activity and stability. The main processes determining urban aerosol fluxes and concentrations are discussed and quantified where possible. The difficulties in parameterising urban activity are discussed.     

Water-soluble organic nitrogen (WSON) in size-segregated atmospheric particles over the Eastern Mediterranean

Atmospheric water-soluble organic nitrogen (WSON) was determined on size-segregated aerosol particles collected during a two years period (2005–2006) in a remote marine location in the Eastern Mediterranean (Finokalia, Crete island). Average concentration of WSON was 5.5 ± 3.9 nmol m^?3 and 11.6 ± 14.0 nmol m^?3 for coarse (PM_1.3-10) and fine (PM_1.3) mode respectively, corresponding to 13% of Total Dissolved Nitrogen (TDN) in both modes. Air masses origin and correlation with tracers of natural and anthropogenic sources indicate that combustion process (biomass burning and fossil fuel) and African dust play an important role in regulating levels of WSON in both coarse and fine aerosol fractions. Chemical speciation of organic nitrogen pool was attempted by analyzing 47 fine aerosol samples (PM₁) for 17 free amino acids (N-FAA), dimethylamine (DMA) and trimethylamine (TMA). The average concentration of N-FAA was 0.5 ± 0.5 nmol m^?3, while the average concentration of DMA was 0.2 ± 0.8 nmol m^?3, TMA was below detection limit. The percentage contribution of N-FAA and DMA to WSON was 2.1 ± 2.3% and 0.9 ± 3.4%, respectively.     

Chemical characteristics of atmospheric aerosols over southwest coast of India

Ambient aerosol samples, collected from Mangalore region in the southwest coast of India during the period of late winter (February and March) to early summer (April and May), have been analysed for water-soluble ionic species. Their abundance pattern is dominated by HCO₃⁻, SO₄²⁻, Na⁺, Cl⁻, with minor contribution from NO₃⁻, Ca²⁺, NH₄⁺, K⁺ and Mg²⁺ indicating the contribution from not only sea salt, but also from anthropogenic and dust sources; with pronounced seasonal variability. The suspended particulate matter concentration varied from 35 to 160 μg m⁻³, with consistently higher values during the late winter. Back trajectory analysis suggests the origin of the air masses shifting from Indo-Gangetic Plains (during late winter) to those from the Arabian Sea and the area around Persian Gulf during April–May. Air masses passing over Northern India (Indo-Gangetic Plains) impart characteristic contribution of ionic species from fossil fuel combustion, biomass burning and eolian dust as asserted by the factor analysis. A detailed study on characterisation of aerosols from south Asian region is rather sparse but essential for modelling the effect of tropospheric aerosols on climate.     

Characterization of aerosol over the Northern South China Sea during two cruises in 2003

Atmospheric transport of trace elements has been found to be an important pathway for their input to the ocean. TSP, PM10, and PM2.5 aerosol samples were collected over the Northern South China Sea in two cruises in 2003 to estimate the input of aerosol from continent to the ocean. About 23 elements and 14 soluble ions in aerosol samples were measured. The average mass concentration of TSP in Cruise I in January (78 μg m⁻³) was ∼twice of that in Cruise II in April (37 μg m⁻³). Together with the crustal component, heavy metals from pollution sources over the land (especially from the industry and automobiles in Guangzhou) were transported to and deposited into the ocean. The atmospheric MSA concentrations in PM2.5 (0.048 μg m⁻³ in Cruise I and 0.043 μg m⁻³ in Cruise II) over Northern South China Sea were comparable to those over other coastal regions. The ratio of non-sea-salt (NSS)-sulfate to MSA is 103-655 for Cruise I and 15-440 for Cruise II in PM2.5 samples, which were much higher than those over remote oceans. The estimated anthropogenic sulfate accounts for 83–98% in Cruise I and 63–95% in Cruise II of the total NSS-sulfate. Fe (II) concentration in the aerosols collected over the ocean ranged from 0.1 to 0.9 μg m⁻³, accounting for 16–82% of the total iron in the aerosol, which could affect the marine biogeochemical cycle greatly.     

Flow patterns influencing the seasonal behavior of surface ozone and carbon monoxide at a coastal site near Hong Kong

Surface O₃ and CO were measured at Cape D’Aguilar, Hong Kong during the period of January 1994 to December1996 in order to understand the temporal variations of surface O₃ and CO in East Asia–West Pacific region. The isentropic backward trajectories were used to isolate different air masses reaching the site and to analyze the long-range transport and photochemical buildup of O₃ on a regional scale. The results show that the diurnal variation of surface O₃ was significant in all seasons with daily O₃ production being about 20 ppbv in fall and 10 ppbv in winter, indicating more active photochemical processes in the subtropical region. The distinct seasonal cycles of O₃ and CO were found with a summer minimum (16 ppbv)–fall maximum (41 ppbv) for O₃ and a summer minimum (116 ppbv)–winter maximum (489 ppbv) for CO. The isentropic backward trajectory cluster analyses suggest that the air masses (associated with regional characteristics) to the site can be categorized into five groups, which are governed by the movement of synoptic weather systems under the influence of the Asian monsoon. For marine-originated air masses (M-SW, M-SE and M-E, standing for marine-southwest, marine-southeast and marine-east, respectively) which always appear in summer and spring, the surface O₃ and CO have relatively lower mixing ratios (18, 16 and 30 ppbv for O₃, 127, 134 and 213 ppbv for CO), while the continental air masses (C-E and C-N, standing for continent-east and continent-north, respectively) usually arrive at the site in winter and fall seasons with higher O₃ (43 and 48 ppbv) and CO (286 and 329 ppbv). The 43 ppbv O₃ and 286 ppbv CO are representative of the regionally polluted continental outflow air mass due to the anthropogenic activity in East Asia, while 17 ppbv O₃ and 131 ppbv CO can be considered as the signature of the approximately clean marine background of South China Sea. The very high CO values (461–508 ppbv) during winter indicate that the long-range transport of air pollutants from China continent is important at the monitoring site. The fall maximum (35–46 ppbv) of surface O₃ was believed to be caused by the effects of the weak slowly moving high-pressure systems which underlie favorable photochemical production conditions and the long-range transport of aged air masses with higher O₃ and its precursors.     

Dry atmospheric inputs of trace metals at the Mediterranean coast of Israel (SE Mediterranean): sources and fluxes

This study presents the first detailed data on aerosol concentrations of trace metals (Cd, Pb, Cu, Zn, Cr, Mn, Fe and Al) at the SE Mediterranean coast of Israel, and assesses their sources and fluxes. Aerosol samples were collected at two sampling stations (Tel-Shikmona and Maagan Michael) along the coast between 1994 and 1997. Two broad categories of aerosol trace metal sources were defined; anthropogenic (Cd, Cu, Pb and Zn) and naturally derived elements (Al, Fe, Mn and Cr). The extent of the anthropogenic contribution was estimated by the degree of enrichment of these elements compared to the average crustal composition (EF_crust). High values (median >100) were calculated for Cd, Pb and Zn, minor values for Cu and relatively low values (<10) for Fe, Mn and Cr. The crustal-derived elements exhibited a statistically significant seasonal pattern of higher concentrations during spring and autumn (e.g. Al concentrations in some cases during these periods were observed to be in excess of 1500 ng m⁻³). In the eastern Mediterranean basin crustal-dominated elements are enriched by 2–3 times while others (Cd and Pb) are comparable to the northwestern Mediterranean. The Pb : Cd ratios of ∼150 are higher than in coastal European sites (60–116) or emission materials (∼50). It is speculated that these differences are attributed mainly to the mixing of crustal material with local and European emissions. At present, it is impossible to quantify the latter two fractions. Back trajectory analysis and the subsequent categorization of two main aerosol populations, ‘European’ and ‘North Africa–Arabian’, exhibited a significantly different geochemical imprint on the aerosol chemical composition. ‘European’-derived air masses indicated significantly higher EF_crust values for Cd and Pb due to the greater anthropogenic character of the aerosol population, with a dilution by crustal material of this population leading to comparatively lower EF_crust values associated with the North African–Arabian air masses.     

Properties of organic matter in PM2.5 at Changdao Island,China—A rural site in the transport path of the Asian continental outflow

Fifty-five seasonal PM_2.5 samples were collected March 2003–January 2004 at Changdao, a resort island located at the demarcation line between Bohai Sea and Yellow Sea in Northern China. Changdao is in the transport path of the continental aerosols heading toward the Pacific Ocean in winter and spring due to the East Asia Monsoon. Solvent-extractable organic compounds (SEOC), organic carbon (OC), elemental carbon (EC) and water-soluble organic carbon (WSOC) were analyzed for source identification based on molecular markers. This data set provides useful information for the downstream site researchers of the Asian continental outflow. Total carbon (TC, OC+EC) was ∼18 μg m⁻³ in winter, ∼9 μg m⁻³ in spring and autumn and a large part of the TC was WSOC (33% in winter, >45% in the other seasons). Winter and spring were the high SEOC seasons with n-fatty acids the highest at ∼290 and ∼170 ng m⁻³, respectively, followed by n-alkanes at ∼210 and ∼90 ng m⁻³, and polycyclic aromatic hydrocarbons (PAHs) were also at high at ∼120 and ∼30 ng m⁻³. High WSOC/TC, low C_18:1/C₁₈ of fatty acids, and low concentrations of labile PAHs such as benzo(a)pyrene, together with back trajectory analysis suggested that the aerosols were aged and transported. PAHs, triterpane and sterane distributions provided evidence that coal burning was the main source of the continental outflow. The detection of levoglucosan and β-sitosterol in nearly all the samples showed the impact of biomass burning.     

An analysis of condensation nuclei levels at Mace Head,Ireland

Condensation nuclei (CN) concentrations measured at Mace Head between 1990 and 1992 are presented. The background CN concentration was found to typically range from 100 to 700 cm^-3. Concentration values were in this range for 55% of the measurement period. No seasonal cycle was observed in the CN concentration values. Concurrent equivalent black carbon (EBC) measurements are used to examine anthropogenic influences on the background CN concentration. Evidence that transatlantic air mass transport influenced the background CN concentration, contributing to increased CN and EBC levels, is shown. During polluted conditions the CN concentration was generally higher than 1000 cm^-3. The principal source for high pollution levels was European air masses arriving at the site. Very high CN concentrations, greater than 50 000 cm^-3, are attributed to local gas-to-particle conversion processes. The characteristics of a number of particle production events are considered. These show that these events are highly photochemical and occur during both clean and polluted conditions. Such production events though infrequent contributed significantly to the total aerosol number concentration.