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.     

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.     

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.     

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.     

Particulate matter and gaseous pollutants during a tropical storm and air pollution episode in Southern Taiwan

Gaseous pollutants and PM_2.5 aerosol particles were investigated during a tropical storm and an air pollution episode in southern Taiwan. Field sampling and chemical analysis of particulate matter and gaseous pollutants were conducted in Daliao and Tzouying in the Kaohsiung area, using a denuder-filter pack system during the period of 22 October to 3 November 2004. Sulfate, nitrate and ammonium were the major ionic species in the PM_2.5, accounting for 46 and 39% of the PM_2.5 for Daliao and Tzouying, respectively. Higher PM_2.5, Cl^?, NO₃^? and NH₄⁺, HNO₂ and NH₃ concentrations were found at night in both stations, whereas higher HNO₃ was found during the day. In general, higher PM_2.5, HCl, NH₃, SO₂, Cl^?, NO₃^?, SO₄^2? and NH₄⁺ concentrations were found in Daliao. The synoptic weather during the experiment was first influenced by Typhoon NOCK-TEN, which resulted in the pollutant concentrations decreasing by about two-thirds. After the tropical thunderstorm system passed, the ambient air quality returned to the previous condition in 12 to 24 h. When there was a strong subsidence accompanied by a high-pressure system, a more stable environment with lower wind speed and mixing height resulted in higher PM_2.5, as well as HNO₂, NH₃, SO₄^2?, Cl^?, NO₃^?, NH₄⁺ and K⁺ concentrations during the episode days. The rainfall is mainly a scavenger of air pollutants in this study, and the stable atmospheric system and the high emission loading are the major reasons for high air pollutant concentrations.     

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.

     

Measurements of gas and aerosol for two weeks in northern China during the winter–spring period of 2000, 2001 and 2002

Intensive measurements of gas and aerosol for 2 weeks were carried out at Qingdao (gas and aerosol in 2000, 2001 and 2002), Fenghuangshan (gas and aerosol in 2000 and 2001), and Dalian (aerosol in 2002) in the winter–spring period. High SO₂ episodes were observed on 18 January 2000 at both Qingdao and Fenghuangshan. According to back trajectory calculations and analysis of gaseous species, high SO₂ episodes were caused by local pollution and transport.Nitrate, sulfate and ammonium were the major species in PM_2.5. Mass fractions of NO₃⁻, nss-SO₄²⁻ and NH₄⁺ at Qingdao in 2002 were 10%, 12% and 5.5% for PM_2.5, respectively, which were higher than that of nss-Ca²⁺ (1%). Chemical compositions observed at Dalian and Fenghuangshan were similar to those at Qingdao. The mass ratio of nss-SO₄²⁻/SO₂ at Qingdao in winter was low (< 1.2), indicating that sulfate was probably produced by the slow oxidation of SO₂ in the gas phase and/or was transported from outside of Qingdao in winter. The equivalent ratio of NH₄⁺ to nss-SO₄²⁻ was 1.39, suggesting that ammonium sulfate was one of the major chemical compositions in PM_2.5. The NO₃⁻/SO₄²⁻ ratio at Qingdao was higher than that at remote places in East Asia. Gas and aerosol data obtained at Fenghuangshan were similar to data at Qingdao, suggesting that emissions from small cities may have a great influence on pollution in northern China.     

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.     

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.     

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.     

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.     

Intraurban variability of PM10 and PM2.5 in an Eastern Mediterranean city

The results of the first large scale chemical characterization of PM10 and PM2.5 at three different sites in the urban city of Beirut, Lebanon, are presented. Between May 2009 and April 2010 a total of 304 PM10 and PM2.5 samples were collected by sampling every sixth day at three different sites in Beirut. Observed mass concentrations varied between 19.7 and 521.2 μg m^? 3 for PM10 and between 8.4 and 72.2 μg m^? 3 for PM2.5, respectively. Inorganic concentrations accounted for 29.7–35.6 μg m^? 3 and 46.0–53.5 μg m^? 3 of the total mass of PM10 and PM2.5, respectively. Intra-city temporal and spatial variations were assessed based on the study of three factors: correlation coefficients (R) for PM and chemical components, coefficient of divergence (CODs), and source apportionment using positive matrix factorization (PMF). Based on R and COD of PM concentrations, the three sites appear homogeneous. However, when individual elements were compared, heterogeneity among sites was found. This latter was attributed to the variability in the percent contribution of biogenic and local anthropogenic source factors such as traffic related sources and dust resuspension. Other factors included the proximity to the Mediterranean sea, the population density and the topographical structure of the city. Hence, despite its small size (20.8 km²), one PM monitoring site does not reflect an accurate PM level in Beirut.     

Long-term measurements of atmospheric PM<Subscript>2.5</Subscript> and its chemical composition in rural Korea

Long-term measurements of ambient particulate matter less than 2.5 μm in diameter (PM_2.5) and its chemical compositions were performed at a rural site in Korea from December 2005 to August 2009. The average PM_2.5 concentration was 31 μg m⁻³ for the whole sampling period, and showed a slightly downward annual trend. The major components of PM_2.5 were organic carbon, SO₄²⁻, NO₃⁻, and NH₄⁺, which accounted for 55 % of total PM_2.5 mass on average. For the top 10 % of PM_2.5 samples, anionic constituents and trace elements clearly increased while carbonaceous constituents and NH₄⁺ remained relatively constant. Both Asian dust and fog events clearly increased PM_2.5 concentrations, but affected its chemical composition differently. While trace elements significantly increased during Asian dust events, NO₃⁻, NH₄⁺ and Cl were dramatically enhanced during fog events due to the formation of saturated or supersaturated salt solution. The back-trajectory based model, PSCF (Potential Source Contribution Function) identified the major industrial areas in Eastern China as the possible source areas for the high PM_2.5 concentrations at the sampling site. Using factor analysis, soil, combustion processes, non-metal manufacture, and secondary PM_2.5 sources accounted for 77 % of the total explained variance.     

Secondary aerosol formation and identification of regional source locations by PSCF analysis in the Indo-Gangetic region of India

Secondary aerosol formation was studied at Allahabad in the Indo-Gangetic region during a field campaign called Land Campaign-II in December 2004 (northern winter). Regional source locations of the ionic species in PM₁₀ were identified by using Potential Source Contribution Function (PSCF analysis). On an average, the concentration of water soluble inorganic ions (sum of anions and cations) was 63.2 μgm⁻³. Amongst the water soluble ions, average NO₃⁻ concentration was the highest (25.0 μgm⁻³) followed by SO₄²⁻ (15.8 μgm⁻³) and NH₄⁺ (13.8 μgm⁻³) concentrations. These species, contributed 87% of the total mass of water soluble species, indicating that most of the water soluble PM₁₀ was composed of NH₄NO₃ and (NH₄)₂SO₄/NH₄HSO₄ or (NH₄)₃H(SO₄)₂ particles. Further, the concentrations of SO₄²⁻, NO₃⁻, and NH4⁺ aerosols increased at high relative humidity levels up to the deliquescence point (∼63% RH) for salts of these species suggesting that high humidity levels favor the conversion and partitioning of gaseous SO₂, NO_x, and NH₃ to their aerosol phase. Additionally, lowering of ambient temperature as the winter progressed also resulted in an increase of NO₃⁻ and NH₄⁺ concentrations, probably due to the semi volatile nature of ammonium nitrate. PSCF analysis identified regions along the Indo-Gangetic Plain (IGP) including Northern and Central Uttar Pradesh, Punjab, Haryana, Northern Pakistan, and parts of Rajasthan as source regions of airborne nitrate. Similar source regions, along with Northeastern Madhya Pradesh were identified for sulfate.     

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.     

Mixing states of cloud interstitial particles between water-soluble and insoluble materials at Mt. Tateyama,Japan: Effects of meteorological conditions

Mixing states of cloud interstitial particles between water-soluble and insoluble materials apparently differ under various cloud-forming conditions. To study the mixing states of cloud interstitial particles, we made observations at Mt. Tateyama, Japan (2300 m a.s.l.) during June 2007 using fog (> 10 μm)-cut inlets. Number concentrations of dried particles (0.3–0.5 μm diameter) selected for less-grown (LG) particles (particles smaller than 0.56 μm diameter at 88% relative humidity) were used to quantify tendencies of the growth characteristics of cloud interstitial particles. Size-segregated soot mass concentrations (< 0.4 and < 1.1 μm) were also measured for cloud interstitial particles. Three samples of cloud interstitial LG particles at 88% RH were investigated for water-soluble and insoluble components using dialysis (extraction) of water-soluble materials with transmission electron microscopy (TEM). For one TEM sample with high fractions of the LG particles and high soot mass concentrations under high precipitation (2–6 mm/h), most particles (0.1–0.5 μm) were found to be water insoluble. More than half of the water-insoluble particles were considered to be soot particles showing chain aggregations of electron-opaque spherules. Regarding the other two TEM samples with low fractions of the LG particles under less intense precipitation (ca. 1 mm/h), most particles were partly water soluble. The scavenging process in the precipitating cloud can change the population of particles left behind, preferentially leaving insoluble particles according to cloud formation conditions.     

Characteristics of the chemical composition and source apportionment of PM2.5 for a one-year period in Wuhan,China

In this study, 123 PM_2.5 filter samples were collected in Wuhan, Hubei province from December 2014 to November 2015. Water- soluble inorganic ions (WSIIs), elemental carbon (EC), organic carbon (OC) and inorganic elements were measured. Source apportionment and back trajectory was investigated by the positive matrix factorization (PMF) model and the hybrid single particle lagrangian integrated trajectory (HYSPLIT) model, respectively. The annual PM_2.5 concentration was 80.5?±?38.2 μg/m³, with higher PM_2.5 in winter and lower in summer. WSIIs, OC, EC, as well as elements contributed 46.8%, 14.8%, 6.7% and 8% to PM_2.5 mass concentration, respectively. SO₄^2?, NO₃^? and NH₄⁺ were the dominant components, accounting for 40.2% of PM_2.5 concentrations. S, K, Cl, Ba, Fe, Ca and I were the main inorganic elements, and accounted for 65.2% of the elemental composition. The ratio of NO₃^?/SO₄^2? was 0.86?±?0.72, indicating that stationary sources play dominant role on PM_2.5 concentration. The ratio of OC/EC was 2.9?±?1.4, suggesting the existence of secondary organic carbon (SOC). Five sources were identified using PMF model, which included secondary inorganic aerosols (SIA), coal combustion, industry, vehicle emission, fugitive dust. SIA, coal combustion, as well as industry were the dominant contributors to PM_2.5 pollution, accounting for 34.7%, 20.5%, 19.6%, respectively.

     

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.

     

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.