Analysis of deep‐drogued satellite‐tracked drifter measurements in the northeast pacific

Abstract

We analyse the trajectories of 24 deep‐drogued, satellite‐tracked drifters launched between 50 and 52°N in the northeast Pacific during June and October 1987. Three aspects of the observed motions at the drogue depths of 100 to 120 m are studied: (i) the spatial structure of the mean and variance velocity fields; (ii) the dispersion and eddy diffusion characteristics of the fluctuating motions; and (iii) the properties of selected mesoscale eddies.

The mean Lagrangian velocity field is consistent with the mean flow pattern derived from the historical dynamic height topography. Fluctuating motions within the region are dominated by mesoscale eddies and meanders. Several instances of persistent O(100 days) westward flowing countercurrents were also observed. Based on the Lagrangian integral time‐ and length scales, drifter motions become decorrelated within a period of 10 days and a separation of 100 km. The mean zonal and meridional integral time‐scales of 4.5 and 3.6 days, respectively, are nearly identical with those obtained by Krauss and Böning (1987) from deep‐drogued drifter tracks in the North Atlantic. Because of the relatively small (<100 cm² s^?2) kinetic energy values in the northeast Pacific, the corresponding mean Lagrangian length scales of 29.4 and 29.9 km are roughly half those for the Atlantic.

The observed drifter dispersion is generally consistent with Taylor's (1921) theory for single‐particle dispersion in homogeneous isotropic turbulence. Estimates obtained using 476 pseudo‐drifter tracks generated from the original records indicate that the dispersion increases linearly with time, t, within the first 3 to 5 days of launch and subsequently increases as t^1/2 (the random‐walk regime) within 10 days of launch. The respective peak zonal and meridional eddy diffusion coefficients of 4.1 × and 3.8 × 10⁷ cm² s^?1 are reached within 30 days of deployment. Similar estimates for the peak eddy diffusivities are obtained using dispersion curves for sets of 4 drifters launched at the same location during the June and October deployments. The dispersion of these clusters followed an exponential rather than a t^1/2 dependence over the first 70 days after release.

Eddies are predominantly clockwise rotary and are characterized by radii of 26 ± 16 km, periods of rotation of 16.0 ± 5.2 days, and azimuthal current speeds of 12.7 ± 8.6 cm s^?1. One eddy was tracked for over 10 months. Oceanographic data collected during the October deployment period showed the eddies have vertical extents of 500 to 700 m and are linked to isotherm depressions of over 100 m in the main pycnocline. All eddies in the bifurcation zone propagate to the west at roughly 1.5 ± 0.4 cm s^?1 counter to the prevailing mean flow and winds. These speeds are consistent with the westward phase speeds of first mode baroclinic planetary (Rossby) waves.     

The transport of water,heat and salt through the strait of Belle Isle

Abstract

We present an analysis of current‐meter, sea‐level and hydrographic data collected in the Strait of Belle Isle and the northeastern Gulf of St Lawrence. From an array of moorings in the Strait from July to October 1980, we calculate a net transport into the Gulf of 0.13 × 10⁶ m³ s^?1 and show that the mean and eddy fluxes of heat through the Strait represented a net loss of heat to the northeastern Gulf. The estimated rate of loss of heat is less than the long‐term mean computed by Bugden (1981) but becomes comparable if adjusted for interannual changes of transport and water temperature. Moreover, the 1980 data permit the permanent tide‐gauge stations in the Strait at West Ste Modeste and Savage Cove to be levelled relative to one another, thus allowing surface currents to be calculated from sea‐level alone. Hence the long‐term wintertime transport into the Gulf can be calculated after fractional effects on the vertical structure of the flow are considered. During an average winter it appears that advection through the Strait can account for about 35% of the Gulf Intermediate Layer. A multiple regression involving average Intermediate Layer temperatures over 9 years suggests that winter air temperature in the Gulf, representative of atmospheric cooling, and sea‐level difference across the Strait, representative of advection, are equally important variables and together account for 50% of the Layer's temperature variability. Analysis of current‐meter, sea‐level and hydrographic data collected in 1975 supports earlier hypotheses that the strongest inflow of water with ? < 0° C and salinity between 32 and 3 3 should occur in winter. It appears that during the 1975 field program the inflow was about 0.6 × 10⁶ m³ s^?1, which is about twice the long‐term average for January to May.     

Methods for Estimating Air–Sea Fluxes of CO<Subscript>2</Subscript> Using High-Frequency Measurements

The most direct method for flux estimation uses eddy covariance, which is also the most commonly used method for land-based measurements of surface fluxes. Moving platforms are frequently used to make measurements over the sea, in which case motion can disturb the measurements. An alternative method for flux estimation should be considered if the effects of platform motion cannot be properly corrected for. Three methods for estimating CO₂ fluxes are studied here: the eddy-covariance, the inertial-dissipation, and the cospectral-peak methods. High-frequency measurements made at the land-based Östergarnsholm marine station in the Baltic Sea and measurements made from a ship during the Galathea 3 expedition are used. The Kolmogorov constant for CO₂, used in the inertial-dissipation method, is estimated to be 0.68 and is determined using direct flux measurements made at the Östergarnsholm site. The cospectral-peak method, originally developed for neutral stratification, is modified to be applicable in all stratifications. With these modifications, the CO₂ fluxes estimated using the three methods agree well. Using data from the Östergarnsholm site, the mean absolute error between the eddy-covariance and inertial-dissipation methods is 0.25 μmol  m^?2 s^?1. The corresponding mean absolute error between the eddy-covariance and cospectral-peak methods is 0.26 μmol m^?2 s^?1, while between the inertial-dissipation and cospectral-peak methods it is 0.14 μmol m^?2 s^?1.     

Vertical eddy diffusivity estimations in Swan river estuary

A field experiment is described in which diapycnal diffusivity is estimated by direct and indirect methods in Swan river estuary, Perth, Western Australia. The microstructure profiles were collected in a narrow and straight part of this estuary using a portable flux profiler (PFP). The profiles were segmented into stationary parts and the rate of vertical eddy diffusivity was estimated for the segments within the pycnocline. The direct measurement showed that instantaneous flux could be positive or negative with a low net rate of vertical eddy diffusivity for mass of about 6.5 × 10⁻⁸ m² s⁻¹. All the indirect methods overestimated this rate. However, within the indirect methods, the method of Osborn yielded the poorest estimate while the method of Osborn and Cox gave the closest estimate.     

Monthly variations of net heat flux at the air‐sea interface in coastal waters near Jeddah,Red Sea

Abstract

Based on 16 years of oceanographic and meteorological data the monthly variations of the net heat flux at the air‐sea interface in coastal waters near Jeddah show that the sea gains an average of about 14 ±2 W m^?2 from April to October and loses about 79± 4W m^?2from November to March. The loss of heat during the winter months is not compensated by the gain during the summer months and therefore leads to an annual average deficit of 25 ± 3 Wm^?2. The gain during summer may not favour the formation of a strong seasonal thermocline.     

Continuous measurement of methane flux over a larch forest using a relaxed eddy accumulation method

We measured the methane flux of a forest canopy throughout a year using a relaxed eddy accumulation (REA) method. This sampling system was carefully validated against heat and CO₂ fluxes measured by the eddy covariance method. Although the sampling system was robust, there were large uncertainties in the measured methane fluxes because of the limited precision of the methane gas analyzer. Based on the spectral characteristics of signals from the methane analyzer and the diurnal variations in the standard deviation of the vertical wind velocity, we found the daytime and nighttime precision of half-hourly methane flux measurements to be approximately 1.2 and 0.7?μg?CH₄?m^?2?s^?1, respectively. Additional uncertainties caused by the dilution effect were estimated to affect the accuracy by as much as 0.21?μg?CH₄?m^?2?s^?1 on a half-hourly basis. Diurnal and seasonal variations were observed in the measured fluxes. The biological emission from plant leaves was not observed in our studies, and thus could be negligible at the canopy-scale exchange. The annual methane sink was 835?±?175?mg?CH₄?m^?2?year^?1 (8.35?kg?CH₄?ha^?1?year^?1), which was comparable to the flux range of 379–2,478?mg?CH₄?m^?2?year^?1 previously measured in other Japanese forest soils. This study indicated that the REA method could be a promising technique to measure canopy scale methane fluxes over forests, but further improvement of precision of the analyzer will be required.     

Local energy exchanges in a shallow,coastal lagoon: Summer conditions

Abstract

Meteorological and hydrographic data from the Indian River lagoon on the Atlantic coast of South Florida are used to describe the magnitude and relative importance of local heat flux processes in a bar‐built estuary for summer conditions. Over a 72‐day period in 1979, the energy gain by absorbed net insolation, averaging 316 W m^‐2 is very nearly balanced by the energy loss due to net long‐wave radiation (‐61 W m^‐2), sensible heat loss (‐54 W m^‐2) and evaporation (‐194 W m^‐2). Day‐to‐day imbalances, however, result in cycles of heating and cooling over time scales on the order of 4–6 days. Water temperatures fluctuate only ±0.5–1.0°C about the seasonal normal, reflecting relatively stable meteorological conditions. Heat energy stored in these estuarine waters in summer months is most highly correlated with the absorption of net insolation.     

Ice drift in Southern Baffin Bay and Davis Strait: Research note

Abstract

Using satellite pictures of Baffin Bay and Davis Strait, ice‐floes were tracked in order to give weekly surface velocities for 1978–1979. The approximate location of the edge of the ice sheet was also determined.

In winter the direction of travel was mainly southward in Davis Strait then, as the summer approached, the edge of the ice sheet retreated northward and floe motion became less clearly defined — even going north on occasion in Baffin Bay.

Near shore speeds along Baffin Island exceeded 50 cm s^‐1 in Davis Strait during November and February. Typical values in the winter/spring period were 10–15 cm s^‐1 between Davis Strait and Hudson Strait. Wind records at nearby shore stations showed directions to be mainly from the northwest, roughly parallel to the Baffin Island coastline.

The study confirms the usefulness of satellite pictures as a data source for modelling surface ice movement and for selecting navigation routes in these northern waters.     

The energy budget of the Sable Island ocean region

The heat exchange between ocean and atmosphere over cold water is studied by calculating all terms in the energy balance twice each day for the year 1971 for the Sable Island region.

The atmospheric long‐wave radiation is relatively constant because of frequent overcast and low clouds. The surface long‐wave balance is markedly negative in winter but slightly positive for a short time in summer, due to strong advection of warm moist air over the cold water. In winter, the turbulent fluxes are directed upwards and are strong, the upward fluxes beginning after the middle of August and lasting until mid‐March. The maximum daily values of latent heat flux are 400 to 500 ly day^?1 (194 to 242 W m^?2), about a third or a quarter of the magnitude over the warmer Gulf Stream water. The summer fluxes are fairly constant and directed downward.

The water of the Labrador Current in the Sable Island region warms substantially from March to September and conversely cools intensely in the period November‐January.

A comparison of the energy exchange for a current and for water without motion shows that the surface temperatures would be similar in summer, and the temperature drop would be about equal until November. From that time on, the surface temperature would level off for a water body with no current, but in actual conditions the surface temperature continues to drop to a late winter minimum of about 1°C.

Atmospheric advection of latent heat was calculated by assuming that the daily precipitation was always caused first by condensation of all locally evaporated water with any remainder being supplied by water‐vapour advection. The main cause for atmospheric heating in the Sable Island area was found to be condensation of imported water vapour. The region is, in summer, a marked sink for atmospheric heat and water content. For water it remains a sink even in winter. For sensible heat it becomes a source from November to March. The warming of the atmosphere is caused by release of latent heat of advected water vapour in the period February‐August. During the months September‐January the heat sources are both water‐vapour advection and surface turbulent terms.     

On the mean and tidal currents in Hudson strait

Abstract

The vertical structures of the mean and tidal flows in Hudson Strait are described from moored current‐meter data collected during an 8‐week period in August to October of 1982. The residual flow in the strongly stratified waters off Quebec is directed along the Strait to the southeast, is highly baroclinic and is concentrated near shore (within an offshore length scale of approximately an internal Rossby radius). Maximum mean speeds of 0.3 m s^?1 were observed near‐surface (30 m). In the weakly stratified waters on the northern side of the Strait along Baffin Island the mean flow is northwestward. The maximum speeds are 0.1 m s^?1 near‐surface (30 m) and the current amplitudes decrease to 0.05 m s^?1 at 100 m. The mean southeastward transport is estimated to be 0.93 ±0.23 × 10⁶ m³ s^?1 with a northwestward transport of 0.82 ± 0.24 × 10⁶ m³ s^?1. Over most of the Strait the across‐channel residual currents are directed towards the Quebec shore with velocities ranging from 0.02 to 0.1 ms^?1. Current variability is dominated by the tides, the M₂ being the major tidal constituent. In the vicinity of the mooring the M₂ tide is primarily barotropic, progressive in nature, and has along‐channel current amplitudes varying across the Strait from 0.20 to 0.45 m s^?1. Observed differences in tidal sea‐level elevations across the Strait can be accounted for by the cross‐channel variations characteristic of Kelvin waves.     

Direct Radiative Effect of Aerosols on Net Ecosystem Carbon Exchange in the Pearl River Delta Region

The environmental impact of aerosols is currently a hot issue that has received worldwide attention. Lacking simultaneous observations of aerosols and carbon flux, the understanding of the aerosol radiative effect of urban agglomeration on the net ecosystem carbon exchange(NEE) is restricted. In 2009-2010, an observation of the aerosol optical property and CO_2 flux was carried out at the Dongguan Meteorological Bureau Station(DMBS) using a sun photometer and eddy covariance systems. The different components of photosynthetically active radiation(PAR),including global PAR(GPAR), direct PAR(DPAR), and scattered PAR(FPAR), were calculated using the Santa Barbara DISORT Atmospheric Radiative Transfer(SBDART) model. The effects of PAR on the NEE between land-atmosphere systems were investigated. The results demonstrated that during the study period the aerosol optical depth(AOD)reduced the DPAR by 519.28±232.89 μmol photons · m~(-2)s~(-1);, but increased the FPAR by 324.93±169.85μmol photons ·m~(-2)s~(-1);, ultimately leading to 194.34±92.62 μmol photons · m~(-2)s~(-1); decrease in the GPAR. All the PARs(including GPAR,DPAR, and FPAR) resulted in increases in the NEE(improved carbon absorption), but the FPAR has the strongest effect with the light use efficiency(LUE) being 1.12 times the values for the DPAR. The absorption of DPAR by the vegetation exhibited photo-inhibition in the radiation intensity 600 photons · m~(-2)s~(-1); in contrast, the absorptions of FPAR did not exhibit apparent photo-inhibition. Compared with the FPAR caused by aerosols, the DPAR was not the primary factor affecting the NEE. On the contrary, the increase in AOD significantly increased the FPAR, enhancing the LUE of vegetation ecosystems and finally promoting the photosynthetic CO_2 absorption.     

Anthropogenic heat in the city of S?o Paulo, Brazil

The main goal of this work is to describe the anthropogenic energy flux (Q _F) in the city of S?o Paulo, Brazil. The hourly, monthly, and annual values of the anthropogenic energy flux are estimated using the inventory method, and the contributions of vehicular, stationary, and human metabolism sources from 2004 to 2007 are considered. The vehicular and stationary sources are evaluated using the primary consumption of energy based on fossil fuel, bio fuel, and electricity usage by the population. The diurnal evolution of the anthropogenic energy flux shows three relative maxima, with the largest maxima occurring early in the morning (??19.9 Wm^?2) and in the late afternoon (??20.3 Wm^?2). The relative maximum that occurs around noontime (??19.6 Wm^?2) reflects the diurnal pattern of vehicle traffic that seems to be specific to S?o Paulo. With respect to diurnal evolution, the energy flux released by vehicular sources (Q _FV) contributes approximately 50% of the total anthropogenic energy flux. Stationary sources (Q _FS) and human metabolism (Q _FM) represent about 41% and 9% of the anthropogenic energy flux, respectively. For 2007, the monthly values of Q _FV, Q _FS, Q _FM, and Q _F are, respectively, 16.8?±?0.25, 14.3?±?0.16, 3.5?±?0.03, and 34.6?±?0.41?MJ?m^?2?month^?1. The seasonal evolution monthly values of Q _FV, Q _FS, Q _FM, and Q _F show a relative minimum during the summer and winter vacations and a systematic and progressive increase associated with the seasonal evolution of the economic activity in S?o Paulo. The annual evolution of Q _F indicates that the city of S?o Paulo released 355.2?MJ?m^?2?year^?1 in 2004 and 415.5?MJ?m^?2?year^?1 in 2007 in association with an annual rate of increase of 19.6?MJ?m^?2?year^?1 (from 2004 to 2006) and 30.5?MJ?m^?2?year^?1 (from 2006 to 2007). The anthropogenic energy flux corresponds to about 9% of the net radiation at the surface in the summer and 15% in the winter. The amplitude of seasonal variation of the maximum hourly value of the diurnal variation increases exponentially with latitude.     

Stable carbon and nitrogen isotopic characteristics of PM2.5 and PM10 in Delhi,India

This study presents the chemical composition (carbonaceous and nitrogenous components) of aerosols (PM_2.5 and PM₁₀) along with stable isotopic composition (δ¹³C and δ¹⁵N) collected during winter and the summer months of 2015–16 to explore the possible sources of aerosols in megacity Delhi, India. The mean concentrations (mean?±?standard deviation at 1σ) of PM_2.5 and PM₁₀ were 223?±?69 µg m^?3 and 328?±?65 µg m^?3, respectively during winter season whereas the mean concentrations of PM_2.5 and PM₁₀ were 147?±?22 µg m^?3 and 236?±?61 µg m^?3, respectively during summer season. The mean value of δ¹³C (range: ??26.4 to ??23.4‰) and δ¹⁵N (range: 3.3 to 14.4‰) of PM_2.5 were ??25.3?±?0.5‰ and 8.9?±?2.1‰, respectively during winter season whereas the mean value of δ¹³C (range: ??26.7 to ??25.3‰) and δ¹⁵N (range: 2.8 to 11.5‰) of PM_2.5 were ??26.1?±?0.4‰ and 6.4?±?2.5‰, respectively during the summer season. Comparison of stable C and N isotopic fingerprints of major identical sources suggested that major portion of PM_2.5 and PM₁₀ at Delhi were mainly from fossil fuel combustion (FFC), biomass burning (BB) (C-3 and C-4 type vegitation), secondary aerosols (SAs) and road dust (SD). The correlation analysis of δ¹³C with other C (OC, TC, OC/EC and OC/WSOC) components and δ¹⁵N with other N components (TN, NH₄⁺ and NO₃^?) are also support the source identification of isotopic signatures.

     

Trace ambient levels of particulate mercury and its sources at a rural site near Delhi

Atmospheric particle-bound mercury levels were measured in PM₁₀ aerosols (HgP) at a rural site (Mahasar, Haryana) during winter 2014–15 and summer 2015. The PM₁₀ HgP was determined by using Differential Pulse Anodic Stripping Voltammetry through standard addition methods while the trace metals were determined by using an Atomic Absorption Spectroscopy. The mass concentrations of HgP varied from 591 to 1533 pg/m³ with an average of 1009?±?306 pg/m³ during the winter, while the mass concentrations of HgP varied from 43 to 826 pg/m³ with an average of 320?±?228 pg/m³ during the summer. However, it is difficult to assess whether these levels are harmful or not because there is no standard value available as National Ambient Air Quality Standard. The higher concentrations of HgP during winters were possibly due to favourable local meteorological conditions for the stagnation of particulate matter in the lower atmosphere and the increased emissions from existing natural or anthropogenic sources, regional sources and long-range transportation. Relatively low concentrations of HgP during summer might be due to increased mixing heights as well as scavenging effect because some light to heavy rain events were observed during summer time sampling. However, among other metals determined, the concentration of HgP was the lowest during both the seasons. The study may be useful in assessing the health impacts of PM₁₀ HgP and other metals.     

A 400-year tree-ring record of the Puelo River summer–fall streamflow in the Valdivian Rainforest eco-region, Chile

The Puelo River is a watershed shared between Chile and Argentina with a mean annual streamflow of 644 m³ s^?1. It has a high ecologic and economic importance, including introduced farmed salmon, tourism, sports fishing and projected hydroelectricity. Using Austrocedrus chilensis and Pilgerodendron uviferum tree-ring records we reconstructed summer–fall (December–May) Puelo River streamflow, which is the first of such reconstructions developed in the Pacific domain of South America. The reconstruction goes back to 1599 and has an adjusted r ² of 0.42. Spectral analysis of the reconstructed streamflow shows a dominant 84-year cycle which explains 25.1% of the total temporal variability. The Puelo River summer–fall streamflow shows a significant correlation (P?>?0.95, 1943–2002) with hydrological records throughout a vast geographic range within the Valdivian eco-region (35 to 46°S). Seasonal Puelo River interannual streamflow variability is related to large-scale oceanic and atmospheric circulation features. Summer–fall streamflows showed a significant negative correlation with the Antarctic Oscillation (AAO), whereas winter–spring anomalies appear to be positively connected with sea surface temperature variations in the tropical Pacific. In general, above- and below-average discharges in winter–spring are related to El Niño and La Niña events, respectively. The temporal patterns of the observed and reconstructed records of the Puelo River streamflow show a general decreasing trend in the 1943–1999 period. Projected circulation changes for the next decades in the Southern Hemisphere would decrease summer–fall Puelo River streamflows with significant impacts on salmon production, tourism and hydropower generation.     

The impacts of urbanization on air quality over the Pearl River Delta in winter: roles of urban land use and emission distribution

In this study, ideal but realistic numerical experiments are performed to explore the relative effects of changes in land use and emission distribution on air quality in the Pearl River Delta (PRD) region in winter. The experiments are accomplished using the Lagrangian particle transport and dispersion model FLEXPART coupled with the Weather Research and Forecasting model under different scenarios. Experiment results show that the maximum changes in daily mean air pollution concentration (as represented by SO₂ concentration) caused by land use change alone reaches up to 2?×?10^?6 g m^?3, whereas changes in concentrations due to the anthropogenic emission distribution are characterized by a maximum value of 6?×?10^?6 g m^?3. Such results reflect that, although the impacts of land use change on air quality are non-negligible, the emission distribution exerts a more significant influence on air quality than land use change. This provides clear implications for policy makers to control urban air pollution over the PRD region, especially for the urban planning in spatial arrangements for reasonable emissions.     

The Asian Dust Aerosol Model 2 (ADAM2) with the use of Normalized Difference Vegetation Index (NDVI) obtained from the Spot4/vegetation data

The operational Asian Dust Aerosol Model (ADAM)1 in Korea Meteorological Administration has been modified to the ADAM2 model to be used as an operational forecasting model all year round not only in Korea but also in the whole Asian domain (70-160°E and 5-60°N) using the routinely available World Meteorological Organization (WMO) surface reporting data and the Spot/vegetation Normalized Difference Vegetation Index (NDVI) data for the period of 9 years from 1998 to 2006. The 3-hourly reporting WMO surface data in the Asian domain have been used to re-delineate the Asian dust source region and to determine the temporal variation of the threshold wind speed for the dust rise. The dust emission reduction factor due to vegetation in different surface soil-type regions (Gobi, sand, loess, and mixed soil) has been determined with the use of NDVI data. It is found that the threshold wind speed for the dust rise varies significantly with time (minimum in summer and maximum in winter) and surface soil types with the highest threshold wind speed of 8.0 m?s^?1 in the Gobi region and the lowest value of 6.0 m?s^?1 in the loess region. The statistical analysis of the spot/vegetation NDVI data enables to determine the emission reduction factor due to vegetation with the free NDVI value that is the NDVI value without the effect of vegetation and the upper limit value of NDVI for the dust rise in different soil-type regions. The modified ADAM2 model has been implemented to simulate two Asian dust events observed in Korea for the periods from 31 March to 2 April 2007 (a spring dust event) and from 29 to 31 December 2007 (a winter dust event) when the observed PM₁₀ concentration at some monitoring sites in the source region exceeds 9,000 μg m^?3. It is found that ADAM2 model successfully simulates the observed high dust concentrations of more than 8,000 μg m^?3 in the dust source region and 600 μg m^?3 in the downstream region of Korea. This suggests that ADAM2 has a great potential for the use of an operational Asian dust forecast model in the Asian domain.     

Vertical Distribution Characteristics of PM<Subscript>2.5</Subscript> Observed by a Mobile Vehicle Lidar in Tianjin,China in 2016

We present mobile vehicle lidar observations in Tianjin, China during the spring, summer, and winter of 2016. Mobile observations were carried out along the city border road of Tianjin to obtain the vertical distribution characteristics of PM_2.5. Hygroscopic growth was not considered since relative humidity was less than 60% during the observation experiments. PM_2.5 profile was obtained with the linear regression equation between the particle extinction coefficient and PM_2.5 mass concentration. In spring, the vertical distribution of PM_2.5 exhibited a hierarchical structure. In addition to a layer of particles that gathered near the ground, a portion of particles floated at 0.6–2.5-km height. In summer and winter, the fine particles basically gathered below 1 km near the ground. In spring and summer, the concentration of fine particles in the south was higher than that in the north because of the influence of south wind. In winter, the distribution of fine particles was opposite to that measured during spring and summer. High concentrations of PM_2.5 were observed in the rural areas of North Tianjin with a maximum of 350 μg m^–3 on 13 December 2016. It is shown that industrial and ship emissions in spring and summer and coal combustion in winter were the major sources of fine particles that polluted Tianjin. The results provide insights into the mechanisms of haze formation and the effects of meteorological conditions during haze–fog pollution episodes in the Tianjin area.     

Refractory Black Carbon Results and a Method Comparison between Solid-state Cutting and Continuous Melting Sampling of a West Antarctic Snow and Firn Core

This work presents the refractory black carbon(rBC)results of a snow and firn core drilled in West Antarctica(79°55'34.6"S,94°21'13.3"W)during the 2014?15 austral summer,collected by Brazilian researchers as part of the First Brazilian West Antarctic Ice Sheet Traverse.The core was drilled to a depth of 20 m,and we present the results of the first 8 m by comparing two subsampling methods—solid-state cutting and continuous melting—both with discrete sampling.The core was analyzed at the Department of Geological Sciences,Central Washington University(CWU),WA,USA,using a single particle soot photometer(SP2)coupled to a CETAC Marin-5 nebulizer.The continuous melting system was recently assembled at CWU and these are its first results.We also present experimental results regarding SP2 reproducibility,indicating that sample concentration has a greater influence than the analysis time on the reproducibility for low rBC concentrations,like those found in the Antarctic core.Dating was carried out using mainly the rBC variation and sulfur,sodium and strontium as secondary parameters,giving the core 17 years(1998?2014).The data show a well-defined seasonality of rBC concentrations for these first meters,with geometric mean summer/fall concentrations of 0.016μg L^?1 and geometric mean winter/spring concentrations of 0.063μg L^?1.The annual rBC concentration geometric mean was 0.029μg L^?1(the lowest of all rBC cores in Antarctica referenced in this work),while the annual rBC flux was 6.1μg m^?2 yr^?1(the lowest flux in West Antarctica records so far).     

Characteristics of Carbonaceous Particles in Beijing During Winter and Summer 2003

Campaigns were conducted to measure Organic Carbon (OC) and Elemental Carbon (EC) in PM2.5 during winter and summer 2003 in Beijing. Modest differences of PM2.5 and PM10 mean concentrations were observed between the winter and summer campaigns. The mean PM2.5/PM10 ratio in both seasons was around 60%, indicating PM2.5 contributed significantly to PM10. The mean concentrations of OC and EC in PM2.5 were 11.2±7.5 and 6.0±5.0μg m-3 for the winter campaign, and 9.4±2.1 and 4.3±3.0 μg m-3 for the summer campaign, respectively. Diurnal concentrations of OC and EC in PM2.5 were found high at night and low during the daytime in winter, and characterized by an obvious minimum in the summer afternoon. The mean OC/EC ratio was 1.87±0.09 for winter and Z39±0.49 for summer. The higher OC/EC ratio in summer indicates some formation of Secondary Organic Carbon (SOC). The estimated SOC was 2.8 μg m-3 for winter and 4.2μg m-3 for summer.