Μm In Summer Research Articles

Seasonal variation of the size distribution of urban particulate matter and associated organic pollutants in the ambient air

Size-segregated samples of urban particulate matter (<0.95, 0.95–1.5, 1.5–3.0, 3.0–7.5, >7.5 μm) were collected in Thessaloniki, northern Greece, during winter and summer of 2007–2008, in order to study the size distribution of organic compounds such as polycyclic aromatic hydrocarbons (PAHs), aliphatic hydrocarbons (AHs) including n-alkanes and the isoprenoids pristane and phytane, organochlorine pesticides (OCPs) and polychlorinated biphenyls (PCBs). All organic compounds were accumulated in the particle size fraction <0.95 μm particularly in the cold season. Particulate matter displayed a bimodal normalized distribution in both seasons with a stable coarse mode located at 3.0–7.5 μm and a fine mode shifting from 0.95–1.5 μm in winter to <0.95 μm in summer. Unimodal normalized distributions, predominant at 0.95–1.5 μm size range, were found for most organic compounds in both seasons, suggesting gas-to-particle transformation after emission. A second minor mode at larger particles (3.0–7.5 μm) was observed for C 19 and certain OCPs suggesting redistribution due to volatilization and condensation.

Seasonal variability of aerosol optical properties over Beijing

The knowledge of aerosol properties at local and regional scale is important in understanding of the global climate change. In this study, the aerosol optical properties over Beijing have been presented from the Aerosol Robotic Network (AERONET) measurements during 2002–2007. The aerosol optical depth (AOD) showed a distinct seasonal variation with high values in spring (March–May) and summer (June–August). The magnitude of Ångström exponent ( α) was found to be relatively high throughout the year and the highest values (1.27) occurred in summer and the lowest (1.0) in spring. The water vapor retrieved from AERONET was found to be highest (2.60 cm) in summer. The fine modes of aerosol volume size distributions showed the highest peak around radius 0.15 μm in spring, autumn (September–November) and winter (December–February), and radius 0.19 μm in summer. The coarse modes showed the maxima peak at radius 3.0 μm in all seasons. The asymmetry factor ( g) has considered as 0.65 at 440, 675, 870 and 1020 nm over Beijing in climate and radiation models. The average values of the single scattering albedo (SSA) at the four wavelengths were taken as 0.89, 0.91, 0.87 and 0.86 in spring, summer, autumn and winter, respectively. Both real and imaginary parts of the refractive index showed low wavelength dependence. The highest averages of real (1.52) and imaginary parts (0.0165) were found in spring and winter respectively in the wavelength range of 440–1020 nm. The aerosol properties over Beijing were found to highly dependent on season, and changes in aerosol properties were mainly attributed to the presence of dust as the main component during the spring season and the dominance of anthropogenic pollutants during the winter season.

Nutrient distributions over the Southwestern South Atlantic continental shelf from Mar del Plata (Argentina) to Itajaí (Brazil): Winter–summer aspects

Nutrient distributions observed at some depths along the continental shelf from 27°05′S (Brazil) to 39°31′S (Argentina) in winter, 2003 and summer, 2004 related to salinity and dissolved oxygen (mL L −1) and saturation (%) data showed remarkable influences of fresh water discharge over the coastal region and in front of the La Plata estuary. In the southern portion of the study area different processes were verified. Upwelling processes caused by ocean dynamics typical of shelf break areas, eddies related to surface dynamics and regeneration processes confirmed by the increase of nutrients and the decrease of dissolved and saturation oxygen data were verified. High silicate concentrations in the surface waters were identified related to low salinities (minimum of 21.22 in winter and 21.96 in summer), confirming the importance of freshwater inputs in this region, especially in winter. Silicate concentration range showed values between 0.00 and 83.52 μM during winter and from 0.00 to 41.16 μM during summer. Phosphate concentrations worked as a secondary trace of terrestrial input and their values varied from 0.00 to 3.30 μM in winter and from 0.03 to 2.26 μM in summer; however, in shallow waters, phosphate indicated more clearly the fresh water influence. The most important information given by nitrate concentrations was the presence of water from SACW upwelling that represents a new source of nutrients for marine primary production. Nitrate maximum values reached 41.96 μM in winter and 33.10 μM in summer. At a depth ∼800 m, high nitrate, phosphate and silicate concentrations were related to Malvinas Current Waters, Subantarctic Shallow Waters and Antarctic Atlantic Intermediate Waters (AAIW). Dissolved oxygen varied from 3.41 to 7.06 mL L −1 in winter and from 2.65 to 6.85 mL L −1 in summer. The percentage of dissolved oxygen saturation in the waters showed values between 48% and 113% in winter and from 46% to135% in summer. The most important primary production was verified in the summer, and situations of undersaturation were mainly observed below 50 m depth and at some points near the coast. The anti-correlation between nutrients and dissolved oxygen which showed evident undersaturation also revealed important potential sites of remineralization processes. The nutrient behaviours showed some aspects of the processes that occur over the Southwestern South Atlantic continental shelf and in their land–sea interfaces between Mar del Plata and Itajaí.

Seasonal characteristics of the physicochemical properties of North Atlantic marine atmospheric aerosols

Seasonal physicochemical characteristics of North Atlantic marine aerosols are presented for the period from January 2002 to June 2004. The aerosol size distribution modal diameters show seasonal variations, 0.031 μm in winter and 0.049 μm in summer for the Aitken mode and 0.103 μm in winter and 0.177 μm in summer for the accumulation mode. The accumulation mode mass also showed a seasonal variation, minimum in winter and maximum in summer. A supermicron sized particle mode was found at 2 μm for all seasons showing 30% higher mass concentration during winter than summer resulting from higher wind speed conditions. Chemical analysis showed that the concentration of sea salt has a seasonal pattern, minimum in summer and maximum in winter because of a dependency of sea‐salt load on wind speeds. By contrast, the non‐sea‐salt (nss) sulphate concentration in fine mode particles exhibited lower values during winter and higher values during midsummer. The water soluble organic carbon (WSOC) and total carbon (TC) analysis also showed a distinctive seasonal pattern. The WSOC concentration during the high biological activity period peaked at 0.2 μgC m−3, while it was lower than 0.05 μgC m−3 during the low biological activity period. The aerosol light scattering coefficient showed a minimum value of 5.5 Mm−1 in August and a maximum of 21 Mm−1 in February. This seasonal variation was due to the higher contribution of sea salt in the MBL during North Atlantic winter. By contrast, aerosols during late spring and summer exhibited larger angstrom parameters than winter, indicating a large contribution of the biogenically driven fine or accumulation modes. Seasonal characteristics of North Atlantic marine aerosols suggest an important link between marine aerosols and biological activity through primary production of marine aerosols.

Dissolved nutrients in the Tweed Estuary, UK: inputs, distributions and effects of residence time

Results are presented from a campaign in which dissolved inorganic nutrients were measured in the Tweed Estuary, UK. The data utilised here were derived from surveys undertaken on a monthly basis from January to August 1997. There was consistency between the nutrient concentrations observed in the freshwater reaches of the tidal estuary and earlier measurements made several km upstream, in the freshwater river. Typically, nitrate was of the order of 100 μM and silicate approximately half this, whereas phosphate and nitrite were typically approximately 1 μM. Seasonal fluctuations in freshwater nitrate and silicate were very large, with concentrations exceeding (respectively) 300 and 100 μM in winter and less than 30 and 10 μM in summer. The estuarine nutrients surveyed followed this general seasonal pattern. A simple box model was used to investigate the temporal behaviour of a hypothetical estuarine nutrient. The model demonstrated that large deviations from the ‘broad-brush’ seasonal pattern for nitrate and silicate could be expected to occur within the estuary as a result of runoff and residence-time variations. The model also demonstrated that mid-estuarine peaks observed in the longitudinal distributions of phosphate could only have arisen as a result of non-freshwater, wastewater phosphate inputs to the estuary. Without this mid-estuarine input, rapid flushing rates would have ensured that transients due to changing freshwater phosphate concentrations, runoff and tides (via the residence time) would have had relatively little impact on the classic, linear ‘conservative’ mixing diagram for the estuary. Conservative mixing was largely applicable to the other nutrients.

Nature of Atmospheric Aerosols over the Desert Areas in the Asian Continent: Chemical State and Number Concentration of Particles Measured at Dunhuang, China

Measurements of aerosol were made in August and October 2001, and January 2002, at Dunhuang, China (40°00′N, 94°30′E), to understand the nature of atmosphericparticles over the desert areas in the Asian continent. Balloon-borne measurements with an optical particle counter suggested that particle size and concentration had a noticeable peak in size range of super micron in not only the boundary mixing layer but also the free troposphere. Thickness of the boundary mixing layer, from distributions of particle concentration, was about 4 km in summer (17 August 2001), about2.5 km in fall (17 October 2001), and about 3 km in winter (11 January 2002), which suggest active mixing of particles near the boundary in summer. Number-size distribution of particleshowed a noticeable peak in the super micron particles size range inthe mixing boundary layer: 0.4–2 particles cm-3 at diameter>1.2 μm in summer, 0.05–4 particles cm-3 at diameter >1.2 μm in fall, and 0.1–5 particles cm-3 at diameter>1.2 μm in winter. In winter strong inversion of atmospherictemperature was found in the height range from the boundary to about 3 km and vertical distribution of particle concentration well corresponded with the temperature distribution. Chemical elements of individual aerosols, which were collectedin the boundary layer atmosphere at Dunhuang (18 October 2001) were analyzed with an electron microscope equipped with EDX. Thosesingle particle analysis suggested that most of the particles with supermicron size were soil particles, and those particles had littlesulfate on its surface. This is a very important different point,comparing with the chemical state of soil particles, which weretransported from the desert area of China to Japan, and showed frequentlythe existence of sulfate on the particle surface. Therefore, it isstrongly suggested that dust particles can be chemically modifiedduring their long-range transport from desert areas to Japan.

Seasonal DOC accumulation in the Black Sea: a regional explanation for a general mechanism

Abstract During three cruises in the Black Sea, organised in July 1995 and April–May 1997, biological and chemical parameters that can influence the carbon budget were measured in the water column on the NW shelf, particularly in the mixing zone with Danube River waters. We observed in early spring (end of April–May) conditions an important input of freshwater organisms that enhanced the microbial activity in the low salinity range. High bacterial activity regenerates nitrogen in the form of nitrates, but is also responsible for an important consumption of ammonium and phosphate, leading to a high N/P ratio and a strong deficit in phosphorus. The consequence is a limitation of phytoplankton development but also a production of carbohydrates that accumulate all along the salinity gradient. These mechanisms are responsible for a seasonal accumulation of dissolved organic carbon (DOC) that increases from 210 μM in winter to about 280 μM in summer. All this excess DOC disappears during winter, probably degraded by bacterial activity. The degradation of carbon-rich organic matter increases the phosphorus demand by bacteria bringing limitation to phytoplankton primary production.

Distribution and reproductive ecology of the Antarctic octocoral Ainigmaptilon antarcticum in the Weddell Sea

The spatial distribution, density and reproductive ecology of Ainigmaptilon antarcticum was studied using samples (colonies) collected during the EASIZ (Ecology of the Antarctic Sea Ice Zone) cruises I, II, and III, (1996, 1998, and 2000). Samples were taken using Agassiz and bottom trawls between 150 and 600 m depth in conjunction with a Remotely Operated Vehicle (ROV, video recording transects). A. antarcticum showed a very patchy distribution with a mean density of 12 per 100 m 2 (SD ± 23) in the study area. This gorgonian species is gonochoric with a sex ratio of 1:1. Two size classes of oocytes in different developmental stages were observed in summer (January to March) and autumn (April to May), ranging from 25 to 700 µm in summer, and from 20 to 900 µm in autumn. Differences in developmental stages among different zones of the colony were observed. The apical and medial part showed the highest fecundity. The distribution of gonad size differed between summer and autumn. The relative frequency of the largest oocyte size class decreased in the autumn samples. No larvae were found. The results are discussed in the context of the relationship between reproductive strategies of marine invertebrates and environmental factors.

Effect of algal deposition on acetate and methane concentrations in the profundal sediment of a deep lake (Lake Constance)

In the profundal sediment ot Lake Constance (143 m depth) the temperature is constant at 4 °C. Despite the constant temperature, CH4 concentrations changed with season between about 120 μM in winter and about 750 μM in summer, measured down to 30 cm depth. The acetate concentration profiles also varied between seasons. In summer, acetate concentration reached a maximum at about 100 μM in 2 or 4 cm depth. In winter, maximal concentrations of about 5 μM were observed over the entire depth. Input of organic material in late spring may be the reason for the seasonal change of both compounds. To simulate such a sedimentation event, intact sediment cores were covered with suspensions of Porphyridium aerugenium or Synechococcus sp. The addition of the phytoplankton material resulted in a drastic increase of acetate concentrations with a maximum at 2 cm depth, similar to in situ acetate concentrations measured in summer. The same applies for CH4 for which increased concentrations were observed down to 6 cm depth. H2 concentrations, on the other hand, showed no distinct increase. Treatment of intact sediment cores with 14C-labeled Synechococcus cells resulted in the formation of 14C-acetate, 14CH4 and 14CO2. Maximum concentrations of 14CH4 were found at 4 cm depth, i.e. just above the depth to which 14C-acetate penetrated. The results show that phytoplankton blooms may cause a seasonal variation of acetate and CH4 in profundal sediments of deep lakes despite the constant low temperature. They also indicate that acetate is the dominant substrate for methanogenic bacteria in the profundal sediments of Lake Constance.

Effect of algal deposition on acetate and methane concentrations in the profundal sediment of a deep lake (Lake Constance)

In the profundal sediment ot Lake Constance (143 m depth) the temperature is constant at 4 °C. Despite the constant temperature, CH 4 concentrations changed with season between about 120 μM in winter and about 750 μM in summer, measured down to 30 cm depth. The acetate concentration profiles also varied between seasons. In summer, acetate concentration reached a maximum at about 100 μM in 2 or 4 cm depth. In winter, maximal concentrations of about 5 μM were observed over the entire depth. Input of organic material in late spring may be the reason for the seasonal change of both compounds. To simulate such a sedimentation event, intact sediment cores were covered with suspensions of Porphyridium aerugenium or Synechococcus sp. The addition of the phytoplankton material resulted in a drastic increase of acetate concentrations with a maximum at 2 cm depth, similar to in situ acetate concentrations measured in summer. The same applies for CH 4 for which increased concentrations were observed down to 6 cm depth. H 2 concentrations, on the other hand, showed no distinct increase. Treatment of intact sediment cores with 14C-labeled Synechococcus cells resulted in the formation of 14C-acetate, 14CH 4 and 14CO 2. Maximum concentrations of 14CH 4 were found at 4 cm depth, i.e. just above the depth to which 14C-acetate penetrated. The results show that phytoplankton blooms may cause a seasonal variation of acetate and CH 4 in profundal sediments of deep lakes despite the constant low temperature. They also indicate that acetate is the dominant substrate for methanogenic bacteria in the profundal sediments of Lake Constance.

Comparison of measured and computed light scattering the Baltic

Mie theory was used to calculate the average scattering functions of suspended particles from the surface layer of the Baltic in summer and winter. Good agreement with data has been achieved in the angle range of ∼ 15° to ∼ 165°. Corresponding average particle size distributions measured using a Coulter counter in the diameter range of 2.5 to 20 μm were used in the calculations. The size distribution of smaller particles and the refractive indices of particles in the entire optically important diameter range were determined using the trial and error method. A refractive index of 1.1 was obtained for both summer and winter particles in the diameter range of 0.1 to 2 μm. The size distributions of these particles, also determined from light scattering, were hyperbolic with a slope of 4.1. The concentration of particles with diameters between 0.1 and 2 μm in summer was about twice that in winter. Refractive indices: 1.05- 0.005i and 1.03-0,01i were obtained for summer particles with diameters between 2 and ∼ 10 pm and over ∼ 10 pm respectively. A refractive index of 1.1 was obtained for winter particles larger than 2 μm. Only particles with diameters in the range of 0.1 to 10 μm contributed significantly to the volume scattering function measured. Particles smaller than ∼ 2 μm dominated light scattering at angles > 10° and larger particles at smaller angles. The calculated volume scattering function at angles smaller than ∼ 15° for the summer particles agreed with the experimental data. Values of the scattering function in this angular range for the winter particles were about half of those measured. This is explained as a consequence of an underestimation of the projected areas of particles when using Coulter counter data in the computation of light scattering. It can be compensated for in the case of summer particles, with a small refractive index and slope of the size distribution, by selecting a higher than actual refractive index of the particles. Such a compensation is not possible in winter for mostly mineral particles whose refractive index and the slope of the size distribution are already high.

Concentration and size variation of condensation nuclei at Mawson, Antarctica

Condensation nucleus (CN) concentrations have been measured at Mawson (67.6°S, 62.9°E) since mid 1981. Weekly median concentrations have an annual cycle with a maximum of around 300 to 400 cm-3 in summer and a minimum of a few tens of particles per cm-3 in winter. In this respect Mawson behaves very much like an Antarctic continental location. Preliminary measurements of the size distribution of CN particles taken over a nine month period suggest a seasonal change in typical particle radius from around 0.01 μm in winter to around 0.04 μm in summer. Diurnal variation in the CN concentration is generally very weak and does not show any systematic relation to the pronounced diurnal variation in wind-speed at Mawson.

Contribution of Particulate Phosphorus (&gt; 250 μm) to the Total Phosphorus Pool in Lake Water

Particulate phosphorus (PP) &gt; 250 μm was concentrated in the euphotic zone of 17 lakes in central Alberta. When the euphotic zone extended below the epilimnion, PP &gt;250 μm was concentrated deep in the euphotic zone. PP &gt; 250 μm was a significant but variable portion of the total phosphorus (TP) pool in individual lakes; thus, samples should be collected from the euphotic zone on several dates to estimate the contribution of PP &gt; 250 μm to the TP pool. As well, the contribution of this fraction varied among lakes: average summer values for the euphotic zone ranged from 3 to 19%. Among lakes, the contribution of large particles to the TP pool decreased proportionally as lake productivity (estimated by chlorophyll a (Chl a)) increased. The relative contribution of PP &gt; 250 μm in summer accounted for a significant portion of the residual variation in the spring TP-summer Chl a relationship but not the summer TP-summer Chl a relationship in the study lakes. These apparently contradictory results can be explained by differences between lakes that mixed intermittently throughout the summer and those that remained permanently thermally stratified during this time.

Annual variation of dissolved free primary amines in estuarine water and sediment.

The concentration of dissolved free primary amines (DFPA), determined as fluorescamine positive material, was quantified during a one year period of a small estuary. In the water, the concentration of DFPA ranged from 1.8 μM in winter, to 26.5 μM in summer. In the sediment, from 16 to 56 μM of DFPA occurred. The concentration varied with depth and season, and in summer months a maximum of DFPA was observed in the redox discontinuity layer. The DFPA peak in water and sediment coincided with maximum of the macrophytal biomass. About 80% of the fluorescamine positive material was identified as amino acids. Origin and distribution of primary amines in the estuarine environment are discussed.