Characterization of water-soluble inorganic ions in size-segregated aerosols in coastal city,Xiamen

The samples of water-soluble inorganic ions (WSIs), including anions (F^?, Cl^?, SO₄^2?, NO₃^?) and cations (NH₄⁺, K⁺, Na⁺, Ca²⁺, Mg²⁺) in 8 size-segregated particle matter (PM), were collected using a sampler (with 8 nominal cut-sizes ranged from 0.43 to 9.0 μm) from October 2008 to September 2009 at five sites in both polluted and background regions of a coastal city, Xiamen. The results showed that particulate matters in the fine mode (PM_2.1, Dp < 2.1 μm) comprised large part of mass concentrations of aerosols, which accounted for 45.56–51.27%, 40.04–60.81%, 42.02–60.81%, and 40.46–57.07% of the total particulate mass in spring, summer, autumn, and winter, respectively. The water-soluble ionic species in the fine mode at five sampling sites varied from 15.33 to 33.82 (spring), 14.03 to 28.06 (summer), 33.47 to 72.52 (autumn), and 48.39 to 69.75 μg m^? 3 (winter), respectively, which accounted for 57.30 ± 6.51% of the PM_2.1 mass concentrations. Secondary pollutants of NH₄⁺, SO₄^2? and NO₃^? were the dominant contributors of WSIs, which suggested that pollutants from anthropogenic activities, such as SO₂, NOx were formed in aerosols by photochemical reactions. The size distributions of Na⁺, Cl^?, SO₄^2? and NO₃^? were bimodal, peaking at 0.43–0.65 μm and 3.3–5.8 μm. Although some ions, such as NH₄⁺ presented bimodal distributions, the coarse mode was insignificant compared to the fine mode. Ca²⁺ and Mg²⁺ exhibited unimodal distributions at all sampling sites, peaking at 2.1–3.3 μm, while K⁺ having a bimodal distributions with a major peak at 0.43–0.65 μm and a minor one at 3.3–4.7 μm, were used in most of samples. Seasonal and spatial variations in the size-distribution profiles suggested that meteorological conditions (seasonal patterns) and sampling locations (geographical patterns) were the main factors determining the formation of secondary aerosols and characteristics of size distributions for WSIs.     

Investigations on meteorological conditions for elevated PM2.5 in Fairbanks,Alaska

The relationships between meteorological conditions (temperature, wind-speed and direction, relative humidity, surface-inversion depth and strength, and stability) and PM_2.5 concentrations in Fairbanks, Alaska were investigated using ten years of observational data. The results show that during wintertime (November through February) PM_2.5 concentrations exceeding the 24 h National Air Quality Standard (35 μg/m³) occurred under calm wind, extremely low temperature (≤20 °C) and moisture (water-vapor pressure < 2 hPa) multiday surface-inversion conditions that trap the pollutants in the breathing level and inhibit transport of polluted air out of Fairbanks. PM_2.5 concentrations tend to be higher under stable than other conditions, but are not sensitive to the degree of stability. The presence of a surface inversion and calm wind are necessary, but in combination with low temperatures and humidity, the conditions are sufficient for high PM_2.5 concentrations. The low temperatures are required because they lead to increased emission rates from domestic heating and power production. During multiday inversions with temperatures above ? 20 °C, high relative humidity (> 75%) partly caused by water-vapor emission reduces PM_2.5 concentrations.     

Concentrations and sources of PAHs at three stations in Istanbul,Turkey

The chemical mass balance model was applied to atmospheric Polycyclic Aromatic Hydrocarbons (PAHs) in Istanbul, Turkey. A total of 326 airborne samples were collected and analyzed for 16 PAHs and Total Suspended Particles (TSP) in the September 2006–December 2007 period at three monitoring stations: Yildiz, DMO (urban sites) and Kilyos (rural site). The total average PAH concentrations were 100.66 ± 61.26, 84.63 ± 46.66 and 25.12 ± 13.34 ng m^?3 and the TSP concentrations were 101.16 ± 53.22, 152.31 ± 99.12, 49.84 ± 18.58 μg m^?3 for Yildiz, DMO and Kilyos stations respectively. At all the sites, the lighter compounds were the most abundant, notably Nap, AcPy and PA. The average correlation values between TSP and total heavier PAH were greater than 0.5 for Yildiz and DMO stations. The patterns of PAH and TSP concentrations showed spatial and temporal variations. PAH concentrations were evaluated for the PAH contribution from four sources (diesel engines, gasoline engines, natural gas combustion, and coal + wood burning). Vehicle emissions appear to be the major source with contributions of 61.2%, 63.3% and 54.1% for Yildiz, DMO and Kilyos stations respectively. Seasonal and yearly variations had different trends for all sites.     

Influence of regional pollution and sandstorms on the chemical composition of cloud/fog at the summit of Mt. Taishan in northern China

Cloud/fog samples were collected during spring of 2007 in the highly polluted North China Plain in order to examine the impact of pollution and dust particles on cloud water chemistry. The volume weighted mean pH of cloud water was 3.68. The cloud acidity was shown to be associated with air mass origins. Cloud water with its air mass trajectories originating from the southern part of China was more acidic than those from northern China. Anthropogenic source and dust had obvious impact on cloud water composition as indicated by the very high mean concentrations of SO₄^2? (1331.65 μeq L^? 1), NO₃^? (772.44 μeq L^? 1), NH₄⁺ (1375.92 μeq L^? 1) and Ca²⁺ (625.81 μeq L^? 1) in the observation periods. During sandstorm days, cloud pH values were relatively high, and the concentrations of all the ions in cloud water reached unusual high levels. Significant decreases in the mass concentrations of PM_2.5 and PM₁₀ were observed during cloud events. The average scavenging ratio for PM_2.5 and PM₁₀ was 52.0% and 55.7%, respectively. Among the soluble ions in fine particles, NO₃^?, K⁺ and NH₄⁺ tend to be more easily scavenged than Ca²⁺ and Na⁺.     

Carbonaceous materials in size-segregated atmospheric aerosols from urban and coastal-rural areas at the Western European Coast

A high-volume cascade impactor, equipped with a PM10 inlet, was used to collect size-segregated aerosol samples during the summer of 2004 at two Portuguese locations: a coastal-rural area (Moitinhos) and an urban area (Oporto). Concentrations of airborne particulate matter (PM), total carbon (TC), organic carbon (OC), elemental carbon (EC), and water-soluble organic carbon (WSOC) were determined for the following particle size ranges: < 0.49, 0.49–0.95, 0.95–3.0, and 3.0–10 µm. The total PM mass concentrations at the urban and coastal-rural sites ranged from 22.8 to 79.6 μg m^− 3 and 19.9 to 28.2 μg m^− 3, respectively, and more than 56% of the total aerosol mass was found in the fractions below 3.0 μm. At both locations the highest concentrations of OC and EC were found in the submicrometer size range. The regional variability for the OC and EC concentrations, with the highest concentrations being found in the urban area, was related to the contribution of local primary sources (mostly traffic emissions). It was also verified an enrichment of the small size particles in WSOC, representing on average 37.3(± 12.4)% and 59.7(± 18.0)% of OC in the very fine aerosol at the coastal-rural and urban areas, respectively. The amount of secondary OC calculated by the minimum OC/EC ratio method indicates that secondary organic aerosol formation was important throughout the study at both sites. The obtained results suggest that long-range transport and favourable summer conditions for photochemical oxidation are key factors determining secondary OC formation in the coastal-rural and urban areas. The ultraviolet absorption properties of the chromophoric constituents of the WSOC fractions were also different among the different particle size ranges and also between the two sampling locations, thus suggesting the strong impact of the diverse emission sources into the composition of the size-segregated organic aerosol.     

Below-cloud rain scavenging of atmospheric aerosols for aerosol deposition models

Below-cloud aerosol scavenging is generally estimated from field measurements using advanced instruments that measure changes in aerosol distributions with respect to rainfall. In this study, we discuss various scavenging mechanisms and scavenging coefficients from past laboratory and field measurements. Scavenging coefficients derived from field measurements (representing natural aerosols scavenging) are two orders higher than that of theoretical ones for smaller particles (D_p < 2 μm). Measured size-resolved scavenging coefficients can be served as a better option to the default scavenging coefficient (e.g. a constant of 10^?4 s^?1 for all size of aerosols, as used in the CALPUFF model) for representing below-cloud aerosol scavenging. We propose scavenging correction parameter (C_R) as an exponential function of size-resolved scavenging coefficients, winds and width in the downwind of the source–receptor system. For a wind speed of 3 m s^?1, C_R decrease with the width in the downwind for particles of diameters D_p < 0.1 μm but C_R does not vary much for particles in the accumulation mode (0.1 < D_p < 2 μm). For a typical urban aerosol distribution, assuming 3 m s^?1 air-flow in the source–receptor system, 10 km downwind width, 2.84 mm h^?1 of rainfall and using aerosol size dependent scavenging coefficients in the C_R, scavenging of aerosols is found to be 16% in number and 24% in volume of total aerosols. Using the default scavenging coefficient (10^?4 s^?1) in the CALPUFF model, it is found to be 64% in both number and volume of total aerosols.     

Size-resolved aerosol chemical concentrations at rural and urban sites in Central California,USA

Aerosol size distributions were measured with Micro Orifice Uniform Deposit Impactor (MOUDI) cascade impactors at the rural Angiola and urban Fresno Supersites in California's San Joaquin Valley during the California Regional PM₁₀/PM_2.5 Air Quality Study (CRPAQS) winter campaign from December 15, 2000 to February 3, 2001. PM_2.5 filter samples were collected concurrently at both sites with Sequential Filter Samplers (SFS). MOUDI nitrate (NO₃⁻) concentrations reached 66 μg/m³ on January 6, 2001 during the 1000–1600 PST (GMT-8) period. Pair-wise comparisons between PM_2.5 MOUDI and SFS concentrations revealed high correlations at the Angiola site (r > 0.93) but more variability (r < 0.85) at the Fresno site for NO₃⁻, sulfate (SO₄⁼), and ammonium (NH₄⁺). Correlations were higher at Fresno (r > 0.87) than at Angiola (r < 0.7) for organic carbon (OC), elemental carbon (EC), and total carbon (TC). NO₃⁻ and SO₄⁼ size distributions in Fresno were multi-modal and wider than the uni-modal distributions observed at Angiola. Geometric mean diameters (GMD) were smaller for OC and EC than for NO₃⁻ and SO₄⁼ at both sites. OC and EC were more concentrated on the lowest MOUDI stage (0.056 µm) at Angiola than at Fresno. The NO₃⁻ GMD increased from 0.97 to 1.02 µm as the NO₃⁻ concentration at Angiola increased from 43 to 66 µg m^− 3 during a PM_2.5 episode from January 4–7, 2001. There was a direct relationship between GMD and NO₃⁻ and SO₄⁼ concentrations at Angiola but no such relationships for OC or EC. This demonstrates that secondary aerosol formation increases both concentration and particle size for the rural California environment.     

Nitrate in groundwater of China: Sources and driving forces

Identifying the sources of reactive nitrogen (N) and quantifying their contributions to groundwater nitrate concentrations are critical to understanding the dynamics of groundwater nitrate contamination. Here we assessed groundwater nitrate contamination in China using literature analysis and N balance calculation in coupled human and natural systems. The source appointment via N balance was well validated by field data via literature analysis. Nitrate was detected in 96% of groundwater samples based on a common detection threshold of 0.2 mg N L^?1, and 28% of groundwater samples exceeded WHO's maximum contaminant level (10 mg N L^?1). Groundwater nitrate concentrations were the highest beneath industrial land (median: 34.6 mg N L^?1), followed by urban land (10.2 mg N L^?1), cropland (4.8 mg N L^?1), and rural human settlement (4.0 mg N L^?1), with the lowest found beneath natural land (0.8 mg N L^?1). During the period 1980–2008, total reactive N leakage to groundwater increased about 1.5 times, from 2.0 to 5.0 Tg N year^?1, in China. Despite that the contribution of cropland to the total amount of reactive N leakage to groundwater was reduced from 50 to 40% during the past three decades, cropland still was the single largest source, while the contribution from landfill rapidly increased from 10 to 34%. High reactive N leakage mainly occurred in relatively developed agricultural or urbanized regions with a large population. The amount of reactive N leakage to groundwater was mainly driven by anthropogenic factors (population, gross domestic product, urbanization rate and land use type). We constructed a high resolution map of reactive N source appointment and this could be the basis for future modeling of groundwater nitrate dynamics and for policy development on mitigation of groundwater contamination.     

Distribution of inorganic nitrogen-containing species in atmospheric particles from an island in the Yellow Sea

In this study, total suspended particles (TSP) and size-segregated atmospheric aerosol samples were measured on Qianliyan Island in the Yellow Sea in spring (April–May), summer (July–August) and fall (October–November) of 2006 and in water (January–February) of 2007. The mass concentration of the TSP varied from 75.6 to 132.0 μg/m³. The average concentration were 9.37 ± 7.56 μg/m³ and 5.32 ± 4.25 μg/m³ for nitrate and ammonium in the TSP, respectively. TSP concentration showed a significant correlation with those of nitrate (n = 27, r = 0.73) and ammonium (n = 27, r = 0.60). The mass-size distribution of atmospheric particles exhibited two modes with an accumulation mode at 0.43–1.1 μm and a coarse mode at 3.3–4.7 μm throughout the sampling months. A bi-modal size distribution of nitrate in concentration occurred in the April–May, October–November and January–February, but a uni-modal size distribution occurred in the August. The uni-modal size distribution of ammonium at 0.43–0.65 μm was observed throughout the sampling months. The average of inorganic nitrogen in mass concentration accounted for 4.0% of the total mass of aerosol particles while ammonium-N was the dominant fraction of TIN (Total Inorganic Nitrogen), contributing to 62–71% of the TIN.     

The origin of sub-surface source waters define the sea–air flux of methane in the Mauritanian Upwelling,NW Africa

Concentrations and flux densities of methane were determined during a Lagrangian study of an advective filament in the permanent upwelling region off western Mauritania. Newly upwelled waters were dominated by the presence of North Atlantic Central Water and surface CH₄ concentrations of 2.2 ± 0.3 nmol L⁻¹ were largely in equilibrium with atmospheric values, with surface saturations of 101.7 ± 14%. As the upwelling filament aged and was advected offshore, CH₄ enriched South Atlantic Central Water from intermediate depths of 100–350 m was entrained into the surface mixed layer of the filament following intense mixing associated with the shelf break. Surface saturations increased to 198.9 ± 15% and flux densities increased from a mean value over the shelf of 2.0 ± 1.1 μmol m⁻² d⁻¹ to a maximum of 22.6 μmol m⁻² d⁻¹. Annual CH₄ emissions for this persistent filament were estimated at 0.77 ± 0.64 Gg which equates to a maximum of 0.35% of the global oceanic budget. This raises the known outgassing intensity of this area and highlights the importance of advecting filaments from upwelling waters as efficient vehicles for air-sea exchange.     

An analysis on the concentration characteristics of PM2.5 in Seoul,Korea from 2005 to 2012

PM2.5 is a big issue as it is considerably more harmful than other sizes of particulate matter. World Health Organization (WHO) recommends 25 μg m^?3 as the daily average concentration, and 10 μg m^?3 per day as an annual average. To keep up with global trends, it is first necessary to understand the current status and characteristics of PM2.5 concentrations in Korea. Using the PM2.5 data measured by Seoul Metropolitan City from November 2005 to March 2012, the author analyzed its statistical characteristics and correlations with other air pollutants. For the time period from 2005 to 2012, the annual average concentration of PM2.5 was 27 μg m^?3, three times the WHO standard. Also, the daily average PM2.5 concentration of 215 days per year also exceeded the WHO standard. However, the number days exceeding the Korean daily average standard of 50 μg m^?3 to be enacted in 2014 was only three. PM2.5 concentration had a high correlation (r = 0.84) with PM10, and also showed high correlations with gaseous pollutants, such as SO₂, NO₂, and CO, but not O₃. This study suggests that the Korean government should strengthen their standard to match the criteria used by WHO.     

Evidence of high PM2.5 strong acidity in ammonia-rich atmosphere of Guangzhou,China: Transition in pathways of ambient ammonia to form aerosol ammonium at [NH4+]/[SO42–] = 1.5

In this study, 24-h PM_2.5 samples were collected using Harvard Honeycomb denuder/filter-pack system during different seasons in 2006 and 2007 at an urban site in Guangzhou, China. The particles collected in this study were generally acidic (average strong acidity ([H⁺]) ~ 70 nmol m^? 3). Interestingly, aerosol sulfate was not fully neutralized in the ammonia-rich atmosphere (NH₃ ~ 30 ppb) and even when NH₄⁺]/[SO₄^2?] was larger than 2. Consequently, strong acidity ([H⁺]) as high as 170 nmol m^? 3 was observed in these samples. The kinetic rate of neutralization of acidity (acidic sulfate) by ambient ammonia was significantly higher than the rate of formation of ammonium nitrate involving HNO₃ and NH₃ for [NH₄⁺]/[SO₄^2?] ≤ 1.5 and much lower for NH₄⁺]/[SO₄^2?] > 1.5. Therefore, higher nitrate principally formed via homogeneous gas phase reactions involving ammonia and nitric acid were observed for [NH₄⁺]/[SO₄^2?] > 1.5. However, little nitrate, probably formed via heterogeneous processes e.g. reaction of HNO₃ with sea salt or crustal species, was observed for [NH₄⁺]/[SO₄^2?] ≤ 1.5. These demonstrate a clear transition in the pathways of ambient ammonia to form aerosol ammonium at [NH₄⁺]/[SO₄^2?] = 1.5 and evidently explain the observed high acidity due to the unneutralized sulfate in the ammonium-rich aerosol (NH₄⁺]/[SO₄^2?] > 1.5). In fact, the measured acidity was almost similar to the excess acid defined as the acid that remains at [NH₄⁺]/[SO₄^2?] = 1.5 due to the un-neutralized fraction of sulfate ([H⁺] = 0.5[SO₄^2?]). The presence of high excess acid and ammonium nitrate significantly lowered the deliquescence relative humidity of ammonium sulfate (from 80% to 40%) in the ammonium-rich samples.     

Exploring the vertical extent of breaking internal wave turbulence above deep-sea topography

A mooring equipped with 200 high-resolution temperature sensors between 6 and 404 m above the bottom was moored in 1890 m water depth above a steep, about 10° slope of Mount Josephine, NE-Atlantic. The sensors have a precision of less than 0.5 mK. They are synchronized via induction every 4 h so that the 400 m range is measured to within 0.02 s, every 1 s. Thin cables and elliptical buoyancy assured vertical mooring motions to be smaller than 0.1 m under maximum 0.2 m s⁻¹ current speeds. The local bottom slope is supercritical for semidiurnal internal tides by a factor of two. Exploring a one-month record in detail, the observations show: 1/semidiurnal tidal dominance in variations of dissipation rate ε, eddy diffusivity K_z and temperature, but no significant correlation between the records of ε and total kinetic energy, 2/a variation with time over four orders of magnitude of 100-m vertically averaged ε, 3/a local minimum in density stratification between 50 and 100 m above the bottom, 4/a gradual decrease in daily or longer averaged ε and K_z by one order of magnitude over a vertical distance of 250 m, upwards from 150 m above the bottom, 5/monthly mean values of <[ε]> = 2 ± 0.5 × 10⁻⁷ m² s⁻³, <[K_z]> = 8 ± 3 × 10⁻³ m² s⁻¹ averaged over the lower 150 m above the bottom.     

One year measurements of aerosol optical properties over an urban coastal site: Effect on local direct radiative forcing

We present results of direct aerosol radiative forcing over a French Mediterranean coastal zone based on one year of continuous observations of aerosol optical properties during 2005–2006. Monthly-mean aerosol optical depth at 440 nm ranged between 0.1 and 0.34, with high Angstrom coefficient (α > 1.2). The single scattering albedo (at 525 nm) estimated at the surface ranged between 0.7 and 0.8, indicating significant absorption. The presence of aerosols over the Mediterranean zone during summer decreases the shortwave radiation reaching the surface by as much as 26 ± 3.9 W m^− 2, and increases the top of the atmosphere reflected radiation by as much as 5.2 ± 1.0 W m^− 2. The shortwave atmospheric absorption translates to an atmospheric heating of 2.5 to 4.6 K day^− 1. Concerted efforts are needed for investigating the possible impact of the increase in heating rate on the maintenance of heat-waves frequently occurring over this coastal region during summer time.     

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 gases and PM2.5-bound metal abundance over a tropical urban environment,South India

Pre and Post-Monsoon levels of ambient SO₂, NO₂, PM_2.5 and the trace metals Fe, Cu, etc. were measured at industrial and residential regions of the Kochi urban area in South India for a period of two years. The mean PM_2.5, SO₂ and NO₂ concentrations across all sites were 38.98?±?1.38 µg/m³, 2.78?±?0.85 µg/m³ and 11.90?±?4.68 µg/m³ respectively, which is lower than many other Indian cities. There was little difference in any on the measured species between the seasons. A few sites exceeded the NAAQS (define acronym and state standard) and most of the sites exceeded WHO (define acronym and state standard) standard for PM_2.5. The average trace metal concentrations (ng/m³) were found to be Fe (32.58)?>?Zn (31.93)?>?Ni (10.13)?>?Cr (5.48)?>?Pb (5.37)?>?Cu (3.24). The maximum concentration of trace metals except Pb were reported in industrial areas. The enrichment factor, of metals relative to crustal material, indicated anthropogenic dominance over natural sources for the trace metal concentration in Kochi’s atmosphere. This work demonstrates the importance of air quality monitoring in this area.

     

Chemical composition of rainwater and anthropogenic influences in Chengdu,Southwest China

A comprehensive study on the chemical compositions of rainwater was carried out from Jan. to Dec. in 2008 in Chengdu, a city located on the acid rain control zone of southwest China. All samples were analyzed for pH and major ions (F^–, Cl^?, NO₃^?, SO₄^2?, K⁺, Na⁺, Ca²⁺, Mg²⁺, and NH₄⁺). The pH increased due to the result of neutralization caused by the base ions. It was observed that Ca²⁺ was the most abundant cation with a VWM value of 196.6 μeq/L (17.3–1568.7 μeq/L), accounting for 49.7% (9.4%–79.2%) of the total cations. SO₄^2? was the most abundant anion with VWM value of 212.8 μeq/L (41.8–1227.6 μeq/L). SO₄^2? and NO₃^? were dominant among the anions, accounting for 90.4%–99.1% of the total measured anions.The concentrations of NO₃^? were higher than the most polluted cities abroad, which indicated Chengdu has been a severe polluted city over the world. The high fuel consumption from urbanization and the rapid increase of vehicles resulted in the high emission of SO₂ and NO_x, which were the precursor of the high concentration of acidic ions NO₃^? and SO₄^2?. It was the main reason of the severe acid rain in Chengdu.The high concentrations of alkaline ions (mainly Ca²⁺, NH₄⁺) in Chengdu city atmosphere have played an important role to neutralize the acidity of rainwater and the pH value has increased by 0.7 units since 1989. It is worth noting that the emission of NO_x from the automobile exhaust is increased and is becoming the important precursor of acid rain now.     

Atmospheric ionic species in PM2.5 and PM1 aerosols in the ambient air of eastern central India

This study elucidates the characteristics of ambient PM_2.5 (fine) and PM₁ (submicron) samples collected between July 2009 and June 2010 in Raipur, India, in terms of water soluble ions, i.e. Na⁺, NH ₄ ⁺ , K⁺, Mg²⁺, Ca²⁺, Cl^?, NO ₃ ^? and SO ₄ ^2? . The total number of PM_2.5 and PM₁ samples collected with eight stage cascade impactor was 120. Annual mean concentrations of PM_2.5 and PM₁ were 150.9?±?78.6 μg/m³ and 72.5?±?39.0 μg/m³, respectively. The higher particulate matter (PM) mass concentrations during the winter season are essentially due to the increase of biomass burning and temperature inversion. Out of above 8 ions, the most abundant ions were SO ₄ ^2? , NO ₃ ^? and NH ₄ ⁺ for both PM_2.5 and PM₁ aerosols; their average concentrations were 7.86?±?5.86 μg/m³, 3.12?±?2.63 μg/m³ and 1.94?±?1.28 μg/m³ for PM_2.5, and 5.61?±?3.79 μg/m³, 1.81?±?1.21 μg/m³ and 1.26?±?0.88 μg/m³ for PM₁, respectively. The major secondary species SO ₄ ^2? , NO ₃ ^? and NH ₄ ⁺ accounted for 5.81%, 1.88% and 1.40% of the total mass of PM_2.5 and 11.10%, 2.68%, and 2.48% of the total mass of PM₁, respectively. The source identification was conducted for the ionic species in PM_2.5 and PM₁ aerosols. The results are discussed by the way of correlations and principal component analysis. Spearman correlation indicated that Cl^? and K⁺ in PM_2.5 and PM₁ can be originated from similar type of sources. Principal component analysis reveals that there are two major sources (anthropogenic and natural such as soil derived particles) for PM_2.5 and PM₁ fractions.     

Size distributions and dry deposition fluxes of water-soluble inorganic nitrogen in atmospheric aerosols in Xiamen Bay,China

Size-segregated aerosol particles were collected using a high volume MOUDI sampler at a coastal urban site in Xiamen Bay, China, from March 2018 to June 2020 to examine the seasonal characteristics of aerosol and water-soluble inorganic ions (WSIIs) and the dry deposition of nitrogen species. During the study period, the annual average concentrations of PM₁, PM_2.5, PM₁₀, and TSP were 14.8?±?5.6, 21.1?±?9.0, 35.4?±?14.2 μg m^?3, and 45.2?±?21.3 μg m^?3, respectively. The seasonal variations of aerosol concentrations were impacted by the monsoon with the lowest value in summer and the higher values in other seasons. For WSIIs, the annual average concentrations were 6.3?±?3.3, 2.1?±?1.2, 3.3?±?1.5, and 1.6?±?0.8 μg m^?3 in PM₁, PM_1-2.5, PM_2.5–10, and PM_>10, respectively. In addition, pronounced seasonal variations of WSIIs in PM₁ and PM_1-2.5 were observed, with the highest concentration in spring-winter and the lowest in summer. The size distribution showed that SO₄^2?, NH₄⁺ and K⁺ were consistently present in the submicron particles while Ca²⁺, Mg²⁺, Na⁺ and Cl^? mainly accumulated in the size range of 2.5–10 μm, reflecting their different dominant sources. In spring, fall and winter, a bimodal distribution of NO₃^? was observed with one peak at 2.5–10 μm and another peak at 0.44–1 μm. In summer, however, the fine mode peak disappeared, likely due to the unfavorable conditions for the formation of NH₄NO₃. For NH₄⁺ and SO₄^2?, their dominant peak at 0.25–0.44 μm in summer and fall shifted to 0.44–1 μm in spring and winter. Although the concentration of NO₃–N was lower than NH₄–N, the dry deposition flux of NO₃–N (35.77?±?24.49 μmol N m^?2 d^?1) was much higher than that of NH₄–N (10.95?±?11.89 μmol N m^?2 d^?1), mainly due to the larger deposition velocities of NO₃–N. The contribution of sea-salt particles to the total particulate inorganic N deposition was estimated to be 23.9—52.8%. Dry deposition of particulate inorganic N accounted for 0.95% of other terrestrial N influxes. The annual total N deposition can create a new productivity of 3.55 mgC m^?2 d^?1, accounting for 1.3–4.7% of the primary productivity in Xiamen Bay. In light of these results, atmospheric N deposition could have a significant influence on biogeochemistry cycle of nutrients with respect to projected increase of anthropogenic emissions from mobile sources in coastal region.

     

Severe weather reports and proximity to deep convection over Northern Argentina

Conventional surface data and quantitative estimations of precipitation are used to document the occurrence and spatial distribution of severe weather phenomena associated with deep moist convection over southeastern South America.Data used in this paper are 24-hour rainfall, maximum hourly gusts and present weather reports from the surface station network for Argentina to the north of 40°S and cover the period 2000–2005. Hourly rainfall estimated with the CMORPH technique (CPC MORPHing technique, R. J. Joyce et al., 2004) is included in the analysis in order to increase the density of the precipitation database from January 2003 to December 2005. Extreme events are detected by means of a 95th-percentile analysis of the 24-hour rainfall and wind; values greater than 30 mm and 25 m s^?1 respectively are considered extreme in the study area. These results are related to the presence of deep convection by considering the 235 K and 218 K cloud shield evolution in Geostationary Operational Environmental Satellite-12 Infrared (GOES-IR) imagery evaluated by the Forecasting and Tracking of Cloud Cluster (FORTRACC) technique. Rainfall above 30 mm day^?1 and present convection-related weather events tend to occur in the northeast of the country.Finally, an analysis is made of the relationship between severe phenomena and the location and lifecycle of Mesoscale Convective Systems (MCSs) defined by the 218 K or 235 K levels. According to the reports, favorable locations for severe weather concentrate to the northeast of the cloud shield anvil centroid although most of the cases are found in the northwest. This feature can be seen in systems with anvil areas larger than 250,000 km² in association to the predominant mid-level wind shear direction from the northwest over the area. Moreover, systems with centers located north of 30°S present a more circular shape while those to the south are more elongated with a NW–SE main axis clearly related to the presence and interaction with frontal zones over the area. Most of the events occur previous to the moment when the systems reach their maximum extension, between 2 and 10 h after the initiation of the system depending on the size of the MCSs.