Average Light Extinction Research Articles

Impacts of PM2.5 Chemical Composition on Aerosol Light Extinction During the Xi’an International Horticultural Expo of China

In this study, we investigated the impacts of PM2.5 chemical composition on aerosol light extinction during the Xi’an International Horticultural Expo of China. The average mass concentration of PM2.5 was 118.1 ± 57.3 µg m-3 during the entire campaign with 23.1% and 40.7% contributed by carbonaceous aerosols and water-soluble inorganic ions. The average light extinction was 957.7 ± 643.5 Mm-1, of which >90% was contributed by the particle light scattering. The light extinction was 1.6 times larger during polluted period than the unpolluted period. The diurnal pattern of the measured light scattering was associated with the anthropogenic activities of daily life and the daily variation of boundary-layer height. Based on the IMPROVE equation, (NH4)2SO4 was the largest contributor to light extinction (35.3%) during the Xi’an International Horticultural Expo, followed by organic matter (33.7%), NH4NO3 (20.5%), EC (6.3%), and fine soil (4.0%). The light extinction produced by (NH4)2SO4, organic matter, and NH4NO3 were 1.8 – 2.5 times larger during polluted period than the unpolluted period. The results indicated that (NH4)2SO4 was the most important chemical composition in PM2.5 affecting the aerosol light extinction during the Xi’an International Horticultural Expo.

Performance evaluation of biomass sorghum in Hawaii and Texas

Although biomass sorghum [Sorghum bicolor (L.) Moench] has been identified as a high yielding bioenergy feedstock crop on the continental USA, there is however lack of conclusive data on its performance in Hawaii (HI). The objectives of this study were to (i) determine the adaptability and productivity of two biomass sorghum hybrids, and (ii) identify the associated crop parameter attributes and environmental factors for high biomass yields. Two comparative trials were conducted, one on Maui island, HI and the other at Temple, Texas (TX). At Temple, the biomass sorghum hybrids responded as expected, growing to heights in excess of 3m and producing average biomass yields of 37.4Mgha−1. The high leaf area indices (LAI, 7.8–9.8) intercepted over 90% incident photosynthetically active radiation (PAR) at LAI >4, while the computed average light extinction coefficient (k) was 0.48. An average plant growth rate (PGR) of 189kg dry biomass ha−1 day-1 was achieved, while the average radiation use efficiency (RUE) was 2.75gMJ−1. In sharp contrast to the results obtained at Temple, the two sorghum hybrids planted on Maui behaved like photoperiod insensitive short day grain sorghums; lower plant heights (<2.0m), LAI (average, 3.8) and PGR prior to heading (average, 41kgha−1 day-1), flowered early (∼90days after planting), and had aboveground biomass yields reduced by 76%. The study underscored the importance of not only choosing the right bioenergy crop species, but also the suitability of target environments, planting date and management practices. The crop parameters determined at Temple can be incorporated into crop and environmental simulation models such as ALMANAC, EPIC/APEX and SWAT to model various biomass sorghum cropping systems and their associated environmental impacts.

Characteristics of Aerosol Optical Properties and Their Chemical Apportionments during CAREBeijing 2006

Field campaigns monitoring the aerosol optical properties and chemical components of PM_(10) were carried out in Beijing in 2006 summer. The average light extinction coefficient b_(ext), dry aerosol scattering coefficient b_(sp) and aerosol absorption coefficient b_(ap) were 895.0 ± 820.8 Mm^(-1), 364.0 ± 324.3 Mm^(-1) and 57.8 ± 31.1 Mm^(-1), respectively. b_(ext), b_(sp) and bap had the similar increasing trend during the formation process of haze. Pronounced diurnal cycles were observed for ω_(550) (aerosol single scattering albedo at 550 nm), b_(sp), b_(ap) and b_(ext). The dry b_(sp) was elevated during the daytime with a maximum mean value of 475.8 Mm^(-1) (LST 06:00). b_(ext), PM_(2.5) mass concentration and PM_(2.5)/PM_(10) ratio increased at night due to continuous emissions of pollutants to the lower nocturnal boundary layer, and decreased during the daytime due to convective mixing. b_(ap) increased at night, and decreased during the daytime and reached the minimum (37 Mm^(-1)) at LST 16:00. The single scattering albedo reached its maximum (0.87) at LST 11:00. This trend was consistent with the SNA (sulfate, nitrate, and ammonium)/PM_(10) ratio and was contrary to the BC (black carbon)/PM_(10) ratio, which demonstrated that secondary pollution largely influenced the scattering ability of aerosols. Ammonium sulfate, ammonium nitrate, organic mass, elemental carbon and coarse mass contributed 26.5%, 15.2%, 21.8%, 16.1% and 20.4% to the total extinction coefficient during clean days, and 44.6%, 22.3%, 13.6%, 10.8% and 8.7% during hazy days. The fractional contributions of ammonium sulfate and ammonium nitrate were significantly higher during the hazy time than those during the clean days. While the fractional contributions of organic mass, elemental carbon and coarse mass were lower during the haze time than those during the clean days.

Chemical compositions and extinction coefficients of PM 2.5 in peri-urban of Xiamen, China, during June 2009–May 2010

The object of this study was to investigate the chemical compositions of PM 2.5 and its correlations with visibility and meteorological parameters in peri-urban of Xiamen, a southeast coastal city, China. PM 2.5 samples were collected monthly from June 2009 to May 2010. The major compositions of PM 2.5 such as water soluble inorganic ions (WSIIs) (F −, Cl −, NO 2 −, NO 3 −, SO 4 2 − , Na +, K +, NH 4 +, Mg 2 + , and Ca 2 + ) and carbonaceous fractions (organic carbon (OC) and elemental carbon (EC)) were determined to estimate their contribution to light extinction coefficients. The results showed that the annual average concentration of PM 2.5 was 86.16 μg/m 3, with monthly individual values ranging from 58.61 μg/m 3 to 109.39 μg/m 3. The correlation analysis showed that PM 2.5 had higher correlations with visibility ( r = − 0.89) and relative humidity ( r = − 0.75), while there was no apparent correlation between PM 2.5 and wind speed. Water soluble inorganic ions and carbonaceous fractions were the major compositions of PM 2.5 accounting for 28.7% and 20.7% of the total PM 2.5 mass, respectively. NO 3 −, SO 4 2 − , and NH 4 + were the major water soluble inorganic ions, accounting for 22.7%, 44.4%, and 17.7% of the total water soluble inorganic ions (TWSIIs), respectively. The average concentrations of secondary organic carbon (SOC) in summer, autumn, winter, and spring in Xiamen were 4.16, 6.48, 13.00 and 8.01 μg/m 3, which accounted for 43.4%, 45.5%, 54.6% and 58.8% of OC, respectively. The annual average light extinction coefficient of PM 2.5 (( b ext) fine particle) was 214.3 Mm − 1 , which was estimated by the IMPROVE algorithm. The average percentage contributions to ( b ext) fine particle were 39.5% for organic mass, 31.4% for ammonium sulfate, 15.3% ammonium nitrate, and 13.9% for elemental carbon.

High time resolution observation and statistical analysis of atmospheric light extinction properties and the chemical speciation of fine particulates

In recent years, the visibility deterioration caused by regional fine particulate pollution becomes one of the crucial air pollution problems in the urban areas of our country. The rapid variation of visibility and fine particulates make it difficult to estimate the relationship between them precisely and accurately unless high time resolution observation data can be accessed. This study aims to fill this gap in the field of atmospheric science by establishing a formula using multiple linear regressions. Excellent fitting goodness (R 2 = 0.913, n = 3167) was obtained using 10 min average of high-resolution real-time light scattering coefficients, light absorption coefficients, main chemical speciation concentration in PM1 and some meteorological parameters from 17 Jan to 16 Feb, 2009. It shows that the average light extinction coefficient during the observation in the winter of Shenzhen was measured to be 290 ± 183 Mm−1, consisting of 72% of light scattering and 21% of absorption. In terms of the percentage contribution of PM1 chemical species to the total light extinction, the organic matter was estimated to be most with an average of 45%, followed by ammonium sulfate with an average of 24%. The contributions of black carbon and ammonium nitrate were 17% and 12%, respectively. Besides, the diurnal variation of light extinction was investigated as well in this study.

국립공원 지역 시정장애 현상의 물리.화학적 특성

National parks provide recreation, health, and science to human being. The provision of beautiful landscape view of the national park improves an economic and social phase of a nation. However, visibility impairment frequently occurred in the national park area of Gyeongju. The purpose of this study is to investigate the physical and the chemical characteristics of visibility reduction observed at the national park area of Gyeongju. Optical, chemical, meteorological characteristics and scenic monitoring were performed at the visibility monitoring station of Gyeongju University located at the Seoak section of Gyeongju national park from April 28 to May 9, 2008. Light extinction, light scattering, and light absorption coefficients were continuously measured using a transmissometer, a nephelometer, and an aethalometer, respectively. In order to investigate the impact of aerosol chemistry on visibility impairment, size-resolved aerosols were collected at intervals of 2-hour (from 8 A.M. to 6 P.M.) and 14-hour (from 6 P.M. to 8 A.M.) interval each sampling day. The average light extinction coefficient and the average visual range were measured to be and during the intensive monitoring period, respectively. It was revealed that sulfate particle was the largest contributor to the light extinction under hazy condition. Organic mass accounted for about 26% of the average light extinction. The mass extinction efficiencies for , , and were estimated to be 9.0, 4.7, and under the consideration of water growth function of hygroscopic aerosols, respectively.

Semi-Continuous Aerosol Measurement for Visibility Variation Using an External Beam PIXE Method

This study introduces the application of a semi-continuous monitoring and analytic technique to examine the elemental composition for a visibility-impairing aerosol. Semi-continuous measurements of the chemical composition for visibility-impairing aerosol were made during the spring period of 19 30 May 2007 in the urban area of Seoul, Korea. These included measurements of the aerosol elemental composition by a proton induced X-ray emission (PIXE) method, of the aerosol ionic composition by ion chromatography (IC) method and of the aerosol carbonaceous composition by a thermal optical transmittance (TOT) method. Light extinction, scattering and absorption coe cients were measured simultaneously with a transmissometer, a nephelometer and an aethalometer, respectively. The average light extinction coe cient and visual range were measured to be 343 186 Mm 1 and 11.8 4.2 km, respectively, during the intensive monitoring period. The average mass concentrations of PM1:0, PM2:5 and PM10 were measured to be 24.0 13.4, 44.6 30.6 and 77.0 56.1 g m 3 and the correlation coe cient r2 of submicron and ne particles to bext were calculated to be relatively higher values of 0.7835 and 0.7824, respectively. However, the value of r2 for coarse particles was a low value of 0.1261. The results revealed that visibility impairment in the urban atmosphere of Seoul was a ected by ne particles, including submicron particles, rather than coarse particles. On a clear day and a hazy day, the mass concentration of mineral dust was not sensitive to variations in bext. On an Asian dust event day, visibility degradation was dominantly caused by increases in the SO2 4 and the NO 3 components between 12:00 and 14:00, during which time they combined with a large loading of mineral dust caused severely reduced visibility. The ability to observe rapid changes in the aerosol composition using semi-continuous aerosol measurements and the PIXE method was helpful in understanding the diurnal variation of visibility.

Influence of meteorological conditions and particulate matter on visual range impairment in Jinan, China

To understand the influence of aerosol particles and meteorological conditions on visual range in Jinan, the capital of Shandong Province, China, PM(2.5) and PM(10) samples were collected from November 2004 to September 2005. The mass concentrations of PM(2.5) and PM(10), concentrations of water-soluble ions in PM(2.5) and concentrations of black carbon (BC) in the atmosphere were analyzed. The decrease of visual range in Jinan results from the combined influence of PM(2.5), PM(10) and meteorological conditions. For the period studied, the average light extinction coefficient, b(ext), which was estimated from an equation developed by the IMPROVE network was 292 Mm(-1). Ammonium sulfate was the major contributor to visual range impairment, accounting for 41%, while ammonium nitrate, particulate organic matter (POM) and BC made comparable contributions accounting for 20%, 22% and 18%, respectively. This highlights the significance of secondary particles ((NH(4))(2)SO(4), NH(4)NO(3), POM) in visual range impairment in Jinan. The data from this study are also compared with the long-term variations of visual range in Jinan from 1961 to 2005.

Fine particulate matter characteristics and its impact on visibility impairment at two urban sites in Korea: Seoul and Incheon

In order to investigate the causes of visibility degradation in the metropolitan area of Seoul, extensive chemical and optical monitoring of aerosol was conducted at two urban sites; Junnong, Seoul and Yonghyun, Incheon during several seasonal intensive monitoring periods between August 2002 and August 2004. Light extinction, scattering, and absorption coefficients were measured simultaneously with a transmissometer, a nephelometer, and an aethalometer, respectively. Continuous aerosol chemical measurement was also made with Sunset elemental carbon/organic carbon (EC/OC) analyzers and on-line ion monitors. The mean light extinction budget for five major aerosol components; ammonium sulfate, ammonium nitrate, fine carbonaceous particles (EC and OC), fine soil, and coarse particle was estimated based on the measurement results. Investigation of the haze level revealed that PM 2.5 mass concentrations at Junnong and Yonghyun measured under the Worst20% condition were approximately twice those of the Best20% condition. The worst visibility condition was well correlated with increases in mass concentrations of sulfate and nitrate, and EC particles. The mass concentration of aerosol components for the Worst20% was measured to be approximately two- to four-fold higher than those for the Best20%. Degree of visibility degradation was also analyzed based on the air mass pathway information obtained using the HYSPLIT model. Average light extinction coefficients under continental air flow condition at the Junnong and Yonghyun sites were the highest values of 704±414 and 773±546 Mm −1, respectively due to increased loading of fine particles. Visibility was greatly improved at both sites when atmosphere was impacted by air mass originated from Pacific Ocean.

Variation in Crown Light Utilization Characteristics among Tropical Canopy Trees

Light extinction through crowns of canopy trees determines light availability at lower levels within forests. The goal of this paper is the exploration of foliage distribution and light extinction in crowns of five canopy tree species in relation to their shoot architecture, leaf traits (mean leaf angle, life span, photosynthetic characteristics) and successional status (from pioneers to persistent). Light extinction was examined at three hierarchical levels of foliage organization, the whole crown, the outermost canopy and the individual shoots, in a tropical moist forest with direct canopy access with a tower crane. Photon flux density and cumulative leaf area index (LAI) were measured at intervals of 0.25-1 m along multiple vertical transects through three to five mature tree crowns of each species to estimate light extinction coefficients (K). Cecropia longipes, a pioneer species with the shortest leaf life span, had crown LAI <0.5. Among the remaining four species, crown LAI ranged from 2 to 8, and species with orthotropic terminal shoots exhibited lower light extinction coefficients (0.35) than those with plagiotropic shoots (0.53-0.80). Within each type, later successional species exhibited greater maximum LAI and total light extinction. A dense layer of leaves at the outermost crown of a late successional species resulted in an average light extinction of 61% within 0.5 m from the surface. In late successional species, leaf position within individual shoots does not predict the light availability at the individual leaf surface, which may explain their slow decline of photosynthetic capacity with leaf age and weak differentiation of sun and shade leaves. Later-successional tree crowns, especially those with orthotropic branches, exhibit lower light extinction coefficients, but greater total LAI and total light extinction, which contribute to their efficient use of light and competitive dominance.

Influence of canopy structure assumptions on predictions from Beer's law. A comparison of deterministic and stochastic simulations

Since Monsi and Saeki introduced the use of Beer's law to describe light extinction in plant canopies, this law has experienced wide use. Many authors have proposed models for describing foliage distribution within the canopy, with many different crown distribution assumptions. This paper explores seven canopy models and the consequences of these canopy models on prediction of light extinction. These seven canopy models range from three-dimensional homogeneity of the entire canopy space to a three-dimensional crowns predicted for each tree. Light extinction predictions using both deterministic and stochastic methods allow examination of different sources of variation within the canopy. Average light extinction at the base of the canopy was found to be equivalent for all models and assumptions. The models varied markedly, however, in the pattern of the average light extinction within the canopy, as well as in the variation expressed at specific points within the canopy. Discussion of the implications of these simulations, given the various assumptions and objectives, provide some suggestion as to the appropriate use of Beer's law.

The Seasonal Dynamics and Composition of Photosynthetic Picoplankton Communities in Temperate Lakes in Ontario, Canada

AbstractThe seasonal abundance and composition of photosynthetic picoplankton (0.2‐2 μm) was compared among five oligotrophic to mesotrophic lakes in Ontario. Epilimnetic picocyanobacteria abundance followed a similar pattern in all lakes; maximum abundance (2‐4 × 105 cells · ml−1) occurred in late summer following a period of rapid, often exponential increase after epilimnetic temperatures reached 20 °C. In half of the lakes picocyanobacteria abundance was significantly correlated with temperature, while in other lakes the presence of a small spring peak resulted in a poor correlation with temperature. In all lakes there was a significant correlation between epilimnetic abundance and day of the year. Correlations with water chemistry parameters (soluble reactive phosphorus, total phosphorus, particulate C: P and C: N) were generally weaker or insignificant. However, in the three lakes with the highest spring nitrate concentrations, a significant negative correlation with nitrate was observed. During summer stratification, picocyanobacteria abundance reached a maximum within the metalimnion and at or above the euphotic zone (1% of incident light) in all lakes. These peaks were not related to nutrient gradients.The average total phytoplankton biomass ranged from 0.5 g m−3 (wet weight) in the most oligotrophic lake to 1.4 g m−3 for the most mesotrophic with picoplankton biomass ranging from 0.01 g m−3 to 0.3 g m−3. Picocyanobacteria biomass comprised 1 to 9 % of total phytoplankton biomass in late summer, but in one year for one lake represented a maximum of 56%. Other photosynthetic picoplankton (unidentified eukaryotes, Chlorella spp. Nannochloris spp.), although less abundant (103 cells · ml−1) than picocyanobacteria, represented biomass equal or greater than that of the picocyanobacteria in spring and early summer. On average, half of the photosynthetic picoplankton biomass was eukaryotic in the more coloured lakes, while in the clear lakes less than 20% was eukaryotic. Among the lakes there was a significant positive correlation between the average light extinction coefficient and the proportion of eukaryotic biomass of the picoplankton.In mesotrophic Jack's Lake, the contribution of picoplankton to the maximum photosynthetic rate ranged from 10 to 47% with the highest values in the spring (47%) and late summer (33%), as a result of eukaryotic picoplankton and picocyanobacteria respectively. Picocyanobacteria cell specific growth rates were high during July (0.6‐0.8 day−1) and losses were close to 80% of the growth rate. Thus, despite low biomass, photosynthetic picoplankton populations appeared to turn over rapidly and potentially contributed significantly to planktonic food webs in early spring and late summer.