Seasonal and annual trends of carbonaceous species of PM<Subscript>10</Subscript> over a megacity Delhi,India during 2010–2017

PM₁₀ samples were collected to characterize the seasonal and annual trends of carbonaceous content in PM₁₀ at an urban site of megacity Delhi, India from January 2010 to December 2017. Organic carbon (OC) and elemental carbon (EC) concentrations were quantified by thermal-optical transmission (TOT) method of PM₁₀ samples collected at Delhi. The average concentrations of PM₁₀, OC, EC and TCA (total carbonaceous aerosol) were 222?±?87 (range: 48.2–583.8 μg m^?3), 25.6?±?14.0 (range: 4.2–82.5 μg m^?3), 8.7?±?5.8 (range: 0.8–35.6 μg m^?3) and 54.7?±?30.6 μg m^?3 (range: 8.4–175.2 μg m^?3), respectively during entire sampling period. The average secondary organic carbon (SOC) concentration ranged from 2.5–9.1 μg m^?3 in PM₁₀, accounting from 14 to 28% of total OC mass concentration of PM₁₀. Significant seasonal variations were recorded in concentrations of PM₁₀, OC, EC and TCA with maxima during winter and minima during monsoon seasons. In the present study, the positive linear trend between OC and EC were recorded during winter (R²?=?0.53), summer (R²?=?0.59) and monsoon (R²?=?0.78) seasons. This behaviour suggests the contribution of similar sources and common atmospheric processes in both the fractions. OC/EC weight ratio suggested that vehicular emissions, fossil fuel combustion and biomass burning could be the major sources of carbonaceous aerosols of PM₁₀ at the megacity Delhi, India. Trajectory analysis indicates that the air mass approches to the sampling site is mainly from Indo Gangetic plain (IGP) region (Uttar Pradesh, Haryana and Punjab etc.), Thar desert, Afghanistan, Pakistan and surrounding areas.     

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.     

Biogenic hydrogen sulphide emissions and non-sea sulfate aerosols over the Indian Sundarban mangrove forest

Temporal variations in atmospheric hydrogen sulphide concentrations and its biosphere-atmosphere exchanges were studied in the World’s largest mangrove ecosystem, Sundarbans, India. The results were used to understand the possible contribution of H₂S fluxes in the formation of atmospheric aerosol of different size classes (e.g. accumulation, nucleation and coarse mode). The mixing ratio of hydrogen sulphide (H₂S) over the Sundarban mangrove atmosphere was found maximum during the post-monsoon season (October to January) with a mean value of 0.59?±?0.02 ppb and the minimum during pre-monsoon (February to May) with a mean value of 0.26?±?0.01 ppb. This forest acted as a perennial source of H₂S and the sediment-air emission flux ranged between 1213?±?276 μg S m^?2 d^?1(December) and 457?±?114 μg S m^?2 d^?1 (August) with an annual mean of 768?±?240 μg S m^?2d^?1. The total annual emissions of H₂S from the Indian Sundarban were estimated to be 1.2?±?0.6 Tg S. The accumulation mode of aerosols was found to be more enriched with non-sea salt sulfate with an average loading of 5.74 μg m^?3 followed by the coarse mode (5.18 μg m^?3) and nucleation mode (1.18 μg m^?3). However, the relative contribution of Non-sea salt sulfate aerosol to total sulfate aerosol was highest in the nucleation mode (83%) followed by the accumulation (73%) and coarse mode (58%). Significant positive relations between H₂S flux and different modes of NSS indicated the likely link between H₂S, a dominant precursor for the non-sea salt sulfate, and non-sea sulfate aerosol particles. An increase in H₂S emissions from the mangrove could result in an increase in enhanced NSS in aerosol and associated cloud albedo, and a decrease in the amount of incoming solar radiation reaching the Sundarban mangrove forest.     

A semi-continuous measurement of gaseous ammonia and particulate ammonium concentrations in PM<Subscript>2.5</Subscript> in the ambient atmosphere

Ammonia has a short residence time in the atmosphere and rapidly neutralizes acid gases that occur near its source, requiring a rapid measurement system for ammonia and particulate ammonium concentrations to better understand their sources, temporal variation of ammonia emissions, and the formation of secondary ammonium aerosols. A semi-continuous measurement system, consisting of a diffusion scrubber, a particle growth chamber, an air-liquid separator, and a fluorescent detector, was developed to determine both gaseous ammonia (NH₃) and particulate ammonium (NH ₄ ⁺ ) in PM_2.5 in the ambient atmosphere of Gwangju, South Korea, during the months of March, April, July, and September of 2007. During the sampling periods, the average concentrations of ammonia and ammonium were found to be 2.33?±?1.29 μg/m³ and 1.89?±?0.99 μg/m³, respectively. Although the average gaseous ammonia concentration was highest in March, the particulate ammonium concentration was higher during the warmer season, reaching 2.08?±?1.07 μg/m³ and 2.32?±?0.94 μg/m³ in April and July, respectively, while only 1.68?±?0.61 μg/m³ in March and 1.24?±?0.99 μg/m³ in September. It is proposed that the higher availability of acid species during the warmer months produced a significant amount of particulate ammonium sulfate. Diurnal fluctuation of ammonia and ammonium during the warmer months showed that their peak time occurred at approximately 10:00 am. Both ammonia and ammonium concentrations were better correlated during the warmer months than during the cooler months. Further, the data suggest that the ammonia and ammonium were measured under well dispersed conditions, and multiple sources contributed to the ammonia at the sampling site.     

Water-soluble inorganic ions of size-differentiated atmospheric particles from a suburban site of Mexico City

During the MILAGRO campaign, March 2006, eight-stage cut impactors were used to sample atmospheric particles at Tecámac (T1 supersite), towards the northeast edge of the Mexico City Metropolitan Area, collecting fresh local emissions and aged pollutants produced in Mexico City. Particle samples were analyzed to determine total mass concentrations of Ca²⁺, Mg²⁺, NH₄ ⁺, K⁺, Cl^?, SO₄ ^2?, and NO₃ ^?. Average concentrations were 22.1 ± 7.2 μg m^?3 for PM₁₀ and 18.3 ± 6.2 μg m^?3 for PM_1.8. A good correlation between PM₁₀ and PM_1.8, without influence from wind patterns, indicates that local emissions are more important than the city’s pollution transported to the site, despite the fact that Tecámac is just 40 km away from Mexico City. A lack of diurnal patterns in the PM_2.5/PM_1.8 ratio supports this conclusion. The inorganic composition of particles suggests that vehicles, soil resuspension, and industries are the main pollutant sources. Finally, the particles were found to be neutralized, in agreement with observations in the Mexico City Metropolitan Area.     

Assessment of PM<Subscript>2.5</Subscript> chemical compositions in Delhi: primary vs secondary emissions and contribution to light extinction coefficient and visibility degradation

Haze-fog conditions over northern India are associated with visibility degradation and severe attenuation of solar radiation by airborne particles with various chemical compositions. PM_2.5 samples have been collected in Delhi, India from December 2011 to November 2012 and analyzed for carbonaceous and inorganic species. PM₁₀ measurements were made simultaneously such that PM_10–2.5 could be estimated by difference. This study analyzes the temporal variation of PM_2.5 and carbonaceous particles (CP), focusing on identification of the primary and secondary aerosol emissions, estimations of light extinction coefficient (b_ext) and the contributions by the major PM_2.5 chemical components. The annual mean concentrations of PM_2.5, organic carbon (OC), elemental carbon (EC) and PM_10–2.5 were found to be 153.6 ± 59.8, 33.5 ± 15.9, 6.9 ± 3.9 and 91.1 ± 99.9 μg m^?3, respectively. Total CP, secondary organic aerosols and major anions (e.g., SO₄ ^2? and NO₃ ^?) maximize during the post-monsoon and winter due to fossil fuel combustion and biomass burning. PM_10–2.5 is more abundant during the pre-monsoon and post-monsoon. The OC/EC varies from 2.45 to 9.26 (mean of 5.18 ± 1.47), indicating the influence of multiple combustion sources. The b_ext exhibits highest values (910 ± 280 and 1221 ± 371 Mm^?1) in post-monsoon and winter and lowest in monsoon (363 ± 110 and 457 ± 133 Mm^?1) as estimated via the original and revised IMPROVE algorithms, respectively. Organic matter (OM =1.6 × OC) accounts for ~39 % and ~48 % of the b_ext, followed by (NH₄)₂SO₄ (~21 % and ~24 %) and EC (~13 % and ~10 %), according to the original and revised algorithms, respectively. The b_ext estimates via the two IMPROVE versions are highly correlated (R² = 0.95, root mean square error = 38 % and mean bias error = 28 %) and are strongly related to visibility impairment (r = ?0.72), mostly associated with anthropogenic rather than natural PM contributions. Therefore, reduction of CP and precursor gas emissions represents an urgent opportunity for air quality improvement across Delhi.     

Quantitative detection of mass concentration of sand-dust storms via wind-profiling radar and analysis of <Emphasis Type="Italic">Z</Emphasis>-<Emphasis Type="Italic">M</Emphasis> relationship

With the aim to achieve quantitative monitoring of sand-dust storms in real time, wind-profiling radar is applied to monitor and study the process of four sand-dust storms in the Tazhong area of the Taklimakan Desert. Through evaluation and analysis of the spatial-temporal distribution of reflectivity factor, it is found that reflectivity factor ranges from 2 to 18 dBz under sand-dust storm weather. Using echo power spectrum of radar vertical beams, sand-dust particle spectrum and sand-dust mass concentration at the altitude of 600 ～ 1500 m are retrieved. This study shows that sand-dust mass concentration reaches 700?μg/m³ under blowing sand weather, 2000?μg/m³ under sand-dust storm weather, and 400?μg/m³ under floating dust weather. The following equations are established to represent the relationship between the reflectivity factor and sand-dust mass concentration: Z?=?20713.5?M ^0.995 under floating dust weather, Z?=?22988.3?M ^1.006 under blowing sand weather, and Z?=?24584.2?M ^1.013 under sand-dust storm weather. The retrieval results from this paper are almost consistent with previous monitoring results achieved by former researchers; thus, it is implied that wind-profiling radar can be used as a new reference device to quantitatively monitor sand-dust storms.     

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.

     

Characterization of chemical properties of atmospheric aerosols over Anmyeon (South Korea), a super site under Global Atmosphere Watch

This paper reports aerosol chemical properties for the first time over a Korean Global Atmosphere Watch (GAW) supersite, Anmyeon (36°32′N; 126° 19′E), during 2003–2004 period. Total suspended Particulates (TSP) showed significant seasonal variation with consistent higher mass concentrations during spring season (average of up to 230?±?190 μg/m³). PM₁₀ also followed similar trend with higher concentrations during spring (average of up to 170?±?130 μg/m³) and showed reduced concentrations during summer. PM_2.5 showed a significant increase during summer (average of up to 60?±?25 μg/m³), which could be due to the influx of fine mode sea salt aerosols associated with the Changma front (summer monsoon). Chemical composition analysis showed enhanced presence of acidic fractions, majorly contributed by sulphates (SO ₄ ^2- ) and nitrates (NO ₃ ^- ) in TSP, PM₁₀ and PM_2.5 during different seasons. Enhanced presence of Calcium (Ca²⁺) was observed during sand storm days during spring. The high correlation obtained on matrix analysis between crustal ions and acidic ions suggests that the ionic compositions over the site are mainly contributed by terrestrial sources of similar origin. The neutralization factors has been estimated to find the extend of neutralization of acidicity by main basic components, and found to have higher value for Ammonium (up to 1.1) in different seasons, indicating significant neutralization of acidic components over the region by NH ₄ ⁺ . Back trajectory analysis has been performed during different seasons to constrain the possible sources of aerosol origin and the results are discussed in detail.     

Study on water-soluble ionic composition of PM10 and related trace gases over Bay of Bengal during W_ICARB campaign

Aerosol (PM₁₀) samples were collected and its precursor gases, i.e., NH₃, NO, NO₂, and SO₂ measured over Bay of Bengal (BoB) during winter months of December 2008 to January 2009 to understand the relationship between particular matter (PM) and precursor gases. The observations were done under the winter phase of Integrated Campaign on Aerosols, gases and Radiation Budget (W_ICARB). The distribution of water-soluble inorganic ionic composition (WSIC) and its interaction with precursor gases over BoB are reported in present case. Average atmospheric concentration of NH₃, NO, NO_2, and SO₂ were recorded as 4.78?±?1.68, 1.89?±?1.26, 0.31?±?0.14, and 0.80?±?0.30?μg?m^?3, whereas WSIC component of PM₁₀, i.e., NH₄ ⁺, SO₄ ^2?, NO₃ ^?, and Cl^? were recorded as 1.96?±?1.66, 8.68?±?3.75, 1.92?±?1.75, and 2.48?±?0.78?μg?m^?3, respectively. In the present case, abundance of nss-SO₄ ^2? in the particulate matter is recorded as 18?%. It suggests the possibility of long-range transport as well as marine biogenic origin. Higher SO₄ ^2?/(SO₂?+?SO₄ ^2?) equivalent molar ratio during the campaign indicates the gas-to-particle conversion with great efficiency over the study region.     

Carbonaceous and inorganic species in PM<Subscript>10</Subscript> during wintertime over Giridih,Jharkhand (India)

Ambient concentrations of organic carbon (OC), elemental carbon (EC) and water soluble inorganic ionic components (WSIC) of PM₁₀ were studied at Giridih, Jharkhand, a sub-urban site near the Indo Gangatic Plain (IGP) of India during two consecutive winter seasons (November 2011–February 2012 and November 2012–February 2013). The abundance of carbonaceous and water soluble inorganic species of PM₁₀ was recorded at the study site of Giridih. During winter 2011–12, the average concentrations of PM₁₀, OC, EC and WSIC were 180.2?±?46.4; 37.2?±?6.2; 15.2?±?5.4 and 18.0?±?5.1 μg m^?3, respectively. Similar concentrations of PM₁₀, OC, EC and WSIC were also recorded during winter 2012–13. In the present case, a positive linear trend is observed between OC and EC at sampling site of Giridih indicates the coal burning, as well as dispersed coal powder and vehicular emissions may be the source of carbonaceous aerosols. The principal components analysis (PCA) also identifies the contribution of coal burning? +?soil dust, vehicular emissions?+?biomass burning and seconday aerosol to PM₁₀ mass concentration at the study site. Backward trajectoy and potential source contributing function (PSCF) analysis indicated that the aerosols being transported to Giridih from upwind IGP (Punjab, Haryana, Uttar Pradesh and Bihar) and surrounding region.     

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.

     

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.

     

Analysis of chemical characteristics of PM<Subscript>2.5</Subscript> in Beijing over a 1-year period

Beijing is one of the largest and most densely populated cities in China. PM_2.5 (fine particulates with aerodynamic diameters less than 2.5 μm) pollution has been a serious problem in Beijing in recent years. To study the temporal and spatial variations in the chemical components of PM_2.5 and to discuss the formation mechanisms of secondary particles, SO₂, NO₂, PM_2.5, and chemical components of PM_2.5 were measured at four sites in Beijing, Dingling (DL), Chegongzhuang (CG), Fangshan (FS), and Yufa (YF), over four seasons from 2012 to 2013. Fifteen chemical components, including organic carbon (OC), elemental carbon (EC), K⁺, NH₄ ⁺, NO₃ ^?, SO₄ ^2?, Cl^?, Al, Ca, Fe, Mg, Na, Pb, Si, and Zn, were selected for analysis. Overall, OC, SO₄ ^2?, NO₃ ^?, and NH₄ ⁺ were dominant among 15 components, the annual average concentrations of which were 22.62 ± 21.86, 19.39 ± 21.06, 18.89 ± 19.82, and 13.20 ± 12.80 μg·m^?3, respectively. Compared with previous studies, the concentrations of NH₄ ⁺ were significantly higher in this study. In winter, the average concentrations of OC and EC were, respectively, 3 and 2.5 times higher than in summer, a result of coal combustion during winter. The average OC/EC ratios over the four sites were 4.9, 7.0, 8.1, and 8.4 in spring, summer, autumn, and winter, respectively. The annual average [NO₃ ^?]/[SO₄ ^2?] ratios in DL, CG, FS, and YF were 1.01, 1.25, 1.08, and 1.12, respectively, which were significantly higher than previous studies in Beijing, indicating that the contribution ratio of mobile source increased in recent years in Beijing. Analysis of correlations between temperature and relative humidity and between SOR ([SO₄ ^2?]/([SO₄ ^2?] + [SO₂])) and NOR ([NO₃ ^?]/([NO₃ ^?] + [NO₂])) indicated that gas-phase oxidation reactions were the major formation mechanism of SO₄ ^2? in spring and summer in urban Beijing, whereas slow gas-phase oxidation reactions and heterogeneous reactions both occurred in autumn and winter. NO₃ ^? was mainly formed through year-round heterogeneous reactions in urban Beijing.     

Parameterisation of incoming longwave radiation over glacier surfaces in the semiarid Andes of Chile

A good understanding of radiation fluxes is important for calculating energy, and hence, mass exchange at glacier surfaces. This study evaluates incoming longwave radiation measured at two nearby glacier stations in the high Andes of the Norte Chico region of Chile. These data are the first published records of atmospheric longwave radiation measurements in this region. Nine previously published optimised parameterisations for clear sky emissivity all produced results with a root mean square error (RMSE) ~20 W?m^?2 and bias within ±5 W m^?2, which is inline with findings from other regions. Six optimised parameterisations for incoming longwave in all sky conditions were trialled for application to this site, five of which performed comparably well with RMSE on daytime data <18 W?m^?2 and bias within ±6 W?m^?2 when applied to the optimisation site and RMSE <20 W?m^?2 and bias within ±10 W m^?2 when applied to the validation site. The parameterisation proposed by Mölg et al. (J Glaciol 55:292-302, 2009) was selected for use in this region. Incorporating the proposed elevation modification into the equation reduced the bias in the modelled incoming longwave radiation for the validation site. It was found that applying the parameterisation optimised in the original work at Kilimanjaro produced good results at both the primary and validation site in this study, suggesting that this formulation may be robust for different high mountain regions.     

Increasing trend of northeast monsoon rainfall over the equatorial Indian Ocean and peninsular India

Peninsular India and Sri Lanka receive major part of their annual rainfall during the northeast monsoon season (October–December). The long-term trend in the northeast monsoon rainfall over the Indian Ocean and peninsular India is examined in the vicinity of global warming scenario using the Global Precipitation Climatology Project (GPCP) dataset available for the period 1979–2010. The result shows a significant increasing trend in rainfall rate of about 0.5 mm day^?1 decade^?1 over a large region bounded by 10 °S–10 °N and 55 °E–100 °E. The interannual variability of seasonal rainfall rate over peninsular India using conventional rain gauge data is also investigated in conjunction to the Indian Ocean dipole. The homogeneous rain gauge data developed by Indian Institute of Tropical Meteorology over peninsular India also exhibit the considerable upward rainfall trend of about 0.4 mm day^?1 decade^?1 during this period. The associated outgoing longwave radiation shows coherent decrease in the order of 2 W?m^?2 decade^?1 over the rainfall increase region.     

Atmospheric abundance of HULIS during wintertime in Indo-Gangetic Plain: impact of biomass burning emissions

This study reports for the first-time the ambient concentrations of HULIS mass (HULIS-OM, Humic-like substances) and HULIS-C (carbon) in PM₁₀ (particulate matter with aerodynamic diameter?≤?10 μm) from the Indo-Gangetic Plain (IGP at Kanpur, wintertime). HULIS extraction followed by purification and isolation protocol with methanol: acetonitrile (1:1 v/v) on HLB (Hydrophilic-Lipophilic Balanced) cartridge has been established. Quantification of HULIS-C was achieved on a total organic carbon (TOC) analyser whereas HULIS-OM was determined gravimetrically. Consistently high recovery (> 90%) of HULIS-C based on analysis of Humic standard (sodium salt of Humic acid) suggested suitability of our established analytical protocol involving solvent extraction, purification and accurate quantification of HULIS. HULIS-OM varied from 17.3–38 μg m^?3 during daytime and from 19.8–40.6 μg m^?3 during night in this study. During daytime the HULIS-OM constituted 20–30% mass fraction of OM_Total and 10–15% of PM₁₀ mass. However, a relatively low contribution of HULIS-OM has been observed during the night. This observation has been attributed to higher concentrations of OM and PM₁₀ in night owing to nighttime chemical reactivity and condensation of organics in conjunction with shallower planetary boundary layer height. Strong correlation of HULIS-C with K⁺_BB (R²?>?0.80) and significant day-night variability of HULIS-C/WSOC ratio in conjunction with air-mass back trajectories (showing transport of pollutants from upwind IGP) suggest biomass burning emission and secondary transformations as important sources of HULIS over IGP. High-loading of atmospheric PM₁₀ (as high as 440 μg m^?3) with significant contribution of water-soluble organic aerosols (WSOC/OC: ~ 0.40–0.80) during wintertime highlights their plausible potential role in fog and haze formation and their impact on regional-scale atmospheric radiative forcing over the IGP.     

Particulate morphology and elemental characteristics: variability at middle Indo-Gangetic Plain

Airborne particulates were monitored at an urban location of middle Indo-Gangetic Plain (IGP) and subsequently analyzed for particulate diversity and mixing states. Exceptionally high particulate loadings were found both in case of coarser (PM₁₀: 157.5 ± 102.9 μgm^?3, n = 46) and finer particulates (PM_2.5: 92.5 ± 49.8 μgm^?3). Based on particulate morphology and elemental composition, five different clusters of particulates namely tarball, soot, sulphur-rich, aluminosilicate and mineral species were found to dominate. Soot particles (0.1–5 μm) were found to be partly coated, having voids filled by coating material without being completely engulfed. A specific type of amorphous, carbonaceous spherules was evident in wintertime fine particulates signifying emissions from biomass burning and wild fire. Traces of S, Na and Ca were found associated with carbonaceous agglomerates suggesting its metal scavenging behavior. Particle laden filters were further processed for metallic and water soluble ionic species to constitute aerosol composition. Coarser particulates were characterized with higher metallic species (9.2–17.8 %), mostly of crustal origin (Ca: 5.5 %; Fe: 1.6 %; Zn: 1.3 % and Na: 3.8 %) while PM_2.5 also revealed their association with metallic components (6.0–14.9 %) having Ca (4.6 %), Fe (0.9 %) and K (0.8 %) as principle constituents. Ca, Na and NH₄ ⁺ found to generate chloride and sulphate salts thus affecting particulate hygroscopicity. Elevated fractions of NO₃ ^? and K⁺ in PM_2.5 signified contribution of biomass burning while presence of Cl^? with carbonaceous aerosols having traces of Si and K denoted contribution of farming and burning practices. Black carbon aerosol exhibited significant seasonal variability (6.9?21.9 μgm^?3) which support larger association of carbonaceous aerosols in particle micrograph.     

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.     

Investigation on semi-direct and indirect climate effects of fossil fuel black carbon aerosol over China

A Regional Climate Chemistry Modeling System that employed empirical parameterizations of aerosol-cloud microphysics was applied to investigate the spatial distribution, radiative forcing (RF), and climate effects of black carbon (BC) over China. Results showed high levels of BC in Southwest, Central, and East China, with maximum surface concentrations, column burden, and optical depth (AOD) up to 14 μg?m^?3, 8 mg?m^?2, and 0.11, respectively. Black carbon was found to result in a positive RF at the top of the atmosphere (TOA) due to its direct effect while a negative RF due to its indirect effect. The regional-averaged direct and indirect RF of BC in China was about +0.81 and ?0.95 W?m^?2, respectively, leading to a net RF of ?0.15 W?m^?2 at the TOA. The BC indirect RF was larger than its direct RF in South China. Due to BC absorption of solar radiation, cloudiness was decreased by 1.33 %, further resulting in an increase of solar radiation and subsequently a surface warming over most parts of China, which was opposite to BC’s indirect effect. Further, the net effect of BC might cause a decrease of precipitation of ?7.39 % over China. Investigations also suggested large uncertainties and non-linearity in BC’s indirect effect on regional climate. Results suggested that: (a) changes in cloud cover might be more affected by BC’s direct effect, while changes in surface air temperature and precipitation might be influenced by BC’s indirect effect; and (b) BC second indirect effect might have more influence on cloud cover and water content compared to first indirect effect. This study highlighted a substantial role of BC on regional climate changes.