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Atmospheric Environment (v.45, #12)
Development and evaluation of a method for hexavalent chromium in ambient air using IC-ICP-MS by Qingyu Meng; Zhihua (Tina) Fan; Brian Buckley; Lin Lin; Lihui Huang; Chang-Ho Yu; Robert Stiles; Linda Bonanno (pp. 2021-2027).
The challenge to quantify ambient airborne Cr(VI) comes from three interrelated issues: sensitivity, selectivity, and stability. In this study, we developed a sensitive and reliable method to measure Cr(VI) in ambient air by optimizing each step involved in measurement. The enriched isotope was employed to determine the recovery and inter-conversion between Cr species (valences) during sampling, sample storage and chemical analysis. Specifically, ambient particles were collected on a 47-mm mixed cellulose ester (MCE) filter that was pre-cleaned by HNO3 (10% v/v) and pre-treated with NaHCO3 (2 g L−1).53Cr(VI) and50Cr(III) isotopes (4 ng each) were spiked on the filter either before or after sampling. Samples were subsequently sonicated in 5 mL HNO3 (pH 4) solution at 60 °C for 40 min, and separated and analyzed for Cr(VI) and Cr(III) by IC-ICP-MS. The method detection limit was 0.08 ng m−3 and the percent difference was <25% for the collocated samples. The recovery of the spiked Cr(VI) and the conversions between Cr(III) and Cr(VI) varied with matrix (clean filter, NIST 1648 PM, and ambient PM), and lower recoveries and higher inter-conversions were found for Cr species spiked before sampling than the post-sampling spikes. These results showed the effects of sampling process and particle matrix on the stability of Cr species. The effects of co-existing PM elements on Cr(VI) recovery and conversion were also examined and discussed. The acid extraction method developed in this study was compared to the ERG carbonate buffer extraction method using53Cr(VI) isotope spiked NIST 1648 PM. The recoveries of53Cr(VI) were 90.9% ± 8.8% ( N = 11) for our acid extraction method and 89.8% ± 10% ( N = 10) for the ERG carbonate buffer extraction, respectively. The ambient Cr(VI) concentrations in an urban area in NJ measured with the developed method are also reported in the manuscript.► The work reports a sensitive and reliable method to measure ambient airborne Cr(VI). ► The method detection limit for Cr(VI) was 0.08 ng m−3. ► The recovery and conversion of Cr(VI) was affected by sampling and PM species. ► Airborne Cr(VI) were 0.44 ± 0.35 ng m−3 in Paterson and 0.40 ± 0.53 ng m−3 in Chester.
Keywords: Hexavalent chromium; Trivalent chromium; Inter-conversion; Stability; Particulate matter (PM); ICP-MS
Impact of Canadian wildfire smoke on air quality at two rural sites in NY State by Vincent A. Dutkiewicz; Liaquat Husain; Utpal K. Roychowdhury; Kenneth L. Demerjian (pp. 2028-2033).
We report high concentrations of black carbon aerosols (BC), present at two rural sites in New York during the last week in May 2010, that are linked to wildfire activity. At Mayville BC from wood smoke was recorded for a total of 20 h from three separate episodes, mean concentration was 1400 ng m−3. These three short events contributed 13% of the BC burden during the month of May. At Whiteface Mountain high concentrations of BC, carbon monoxide gas (CO), and fine particulate matter mass (PM2.5) are reported from a heavy smoke event that impacted the Adirondack region of the State on May 31, 2010. PM2.5 mass recorded at the Lodge site (600 m above mean sea level) was 150 μg m−3 at 8:30 am EST and the 24-h mean was almost twice the USEPA limits while CO concentration exceeded 1000 ppb and BC concentration reached 9600 ng m−3. The event was delayed several hours at the Summit site (1500 m above mean sea level) but at 5:45 pm BC concentration reached 1600 ng m−3 and CO was 317 ppbv. Detailed temporal profiles and correlations are presented.► We report wildfire smoke from Canada impacting Whiteface Mt., NY on 31 May 2010. ► At WFM lodge (0.6 km amsl) extremely high PM2.5 mass, (150 μg m−3) was recorded. ► The 24-h average PM2.5 mass was 68 μg m−3or higher than the fine PM standard. ► BC reached 9600 ng m−3 at the lodge and 1600 ng m−3 at the summit (1.5 km amsl). ► We estimate that OC concentration at the lodge must have peaked at 75–120 μg m−3.
Keywords: Black carbon; Wildfire smoke; Aerosols; Fine particulate matter; Carbon monoxide; Air quality
Short-term exposure to PM10, PM2.5, ultrafine particles and CO2 for passengers at an intercity bus terminal by Yu-Hsiang Cheng; Hsiao-Peng Chang; Cheng-Ju Hsieh (pp. 2034-2042).
The Taipei Bus Station is the main transportation hub for over 50 bus routes to eastern, central, and southern Taiwan. Daily traffic volume at this station is about 2500 vehicles, serving over 45,000 passengers daily. The station is a massive 24-story building housing a bus terminal, a business hotel, a shopping mall, several cinemas, offices, private residential suites, and over 900 parking spaces. However, air quality inside this bus terminal is a concern as over 2500 buses are scheduled to run daily. This study investigates the PM10, PM2.5, UFP and CO2 levels inside and outside the bus terminal. All measurements were taken between February and April 2010. Measurement results show that coarse PM inside the bus terminal was resuspended by the movement of large numbers of passengers. The fine and ultrafine PM in the station concourse were from outside vehicles. Moreover, fine and ultrafine PM at waiting areas were exhausted directly from buses in the building. The CO2 levels at waiting areas were likely elevated by bus exhaust and passengers exhaling. The PM10, PM2.5 and CO2 levels at the bus terminal were lower than Taiwan’s EPA suggested standards for indoor air quality. However, UFP levels at the bus terminal were significantly higher than those in the urban background by about 10 times. Therefore, the effects of UFPs on the health of passengers and workers must be addressed at this bus terminal since the levels of UFPs are higher than >1.0 × 105 particles cm−3.► Coarse PM inside the bus terminal was resuspended by the movement of large numbers of passengers. ► The CO2 levels at waiting areas were likely elevated by bus exhaust and passengers exhaling. ► UFP levels at the bus terminal were significantly higher than those in the urban background by about 10 times.
Keywords: PM; 10; PM; 2.5; Ultrafine particle; CO; 2; Bus terminal; Taipei
Water-soluble ions measured in fine particulate matter next to cement works by N. Galindo; E. Yubero; J.F. Nicolás; J. Crespo; C. Pastor; A. Carratalá; M. Santacatalina (pp. 2043-2049).
PM2.5 samples were collected for one year in a suburban area close to an industrial complex formed by two cement factories and some quarries in southeastern Spain. Samples were analyzed by ion chromatography to determine the concentrations of major inorganic ions: Cl−, NO3−, SO42−, Na+, NH4+, K+, Mg2+ and Ca2+. The average PM2.5 concentration (17.6 μg m−3) was within the interval reported for other Mediterranean suburban environments. Concentration peaks were registered during both winter and summer, concurrently with maxima levels of nitrate and sulfate, due to stagnation conditions and African dust episodes, respectively. Sulfate was found to be a main contributor to PM2.5 aerosol mass (4.2 μg m−3, 24%), followed by nitrate and ammonium (1.5 μg m−3, 9% each one). Correlation analyses demonstrated that fine sulfate was present as (NH4)2SO4, CaSO4 and Na2SO4 since ammonium concentrations were not high enough to neutralize both anions. The mean concentration of calcium (1.0 μg m−3), an element commonly found in the coarse fraction, was higher than those found in other locations of the Mediterranean basin. Additionally, the lowest levels were registered during summer, in contrast with previous findings. This was attributed to resuspension and transport of mineral dust from the neighboring quarries and cement plants during fall and winter, which was supported by the results of the CPF analysis. Atmospheric levels of potassium and chloride (0.28 and 0.51 μg m−3 annual average, respectively) also seemed to be affected by cement works, as suggested by correlation and CPF analyses. In the case of Cl−, a marked seasonality was observed, with mean winter concentrations considerably higher than summer ones, indicating a clear prevalence of anthropogenic sources over sea spray emissions.► The influence of cement works on PM2.5 and inorganic ions has been investigated. ► Correlation and CPF analyses provided information about sources of PM2.5 ions. ► An effect of these activities on fine Ca2+ levels and its seasonal cycle was found. ► Sulfate levels could have been affected by the cement works at a regional scale.
Keywords: PM2.5; Inorganic ions; Cement plants; Conditional probability function (CPF)
A novel, fuzzy-based air quality index (FAQI) for air quality assessment by Mohammad Hossein Sowlat; Hamed Gharibi; Masud Yunesian; Maryam Tayefeh Mahmoudi; Saeedeh Lotfi (pp. 2050-2059).
The ever increasing level of air pollution in most areas of the world has led to development of a variety of air quality indices for estimation of health effects of air pollution, though the indices have their own limitations such as high levels of subjectivity. Present study, therefore, aimed at developing a novel, fuzzy-based air quality index (FAQI11Fuzzy-based air quality index (FAQI).) to handle such limitations. The index developed by present study is based on fuzzy logic that is considered as one of the most common computational methods of artificial intelligence. In addition to criteria air pollutants (i.e. CO, SO2, PM10, O3, NO2), benzene, toluene, ethylbenzene, xylene, and 1,3-butadiene were also taken into account in the index proposed, because of their considerable health effects. Different weighting factors were then assigned to each pollutant according to its priority. Trapezoidal membership functions were employed for classifications and the final index consisted of 72 inference rules. To assess the performance of the index, a case study was carried out employing air quality data at five different sampling stations in Tehran, Iran, from January 2008 to December 2009, results of which were then compared to the results obtained from USEPA air quality index (AQI). According to the results from present study, fuzzy-based air quality index is a comprehensive tool for classification of air quality and tends to produce accurate results. Therefore, it can be considered useful, reliable, and suitable for consideration by local authorities in air quality assessment and management schemes.► FAQI minimizes subjectivity of conventional indices like USEPA AQI. ► The index can consider the interactions between parameters included. ► Both criteria air pollutants and hazardous pollutants like BTEX are included. ► More accurate results can be obtained using this index, compared to USEPA AQI.
Keywords: Air quality index; Fuzzy logic; Fuzzy inference system; Health effects; Air pollution
Ambient organic carbon to elemental carbon ratios: Influences of the measurement methods and implications by Yuan Cheng; Ke-bin He; Feng-kui Duan; Mei Zheng; Zhen-yu Du; Yong-liang Ma; Ji-hua Tan (pp. 2060-2066).
Ambient organic carbon (OC) to elemental carbon (EC) ratios include important information about the extent of secondary organic aerosol (SOA) production. Influences of the measurement methods on the OC to EC ratios were evaluated in Beijing. When analyzed by the IMPROVE-A temperature protocol, the presence of positive artifact would increase the OC to EC ratio by 14–36% based on the transmittance correction, whereas the ratio of the un-denuded filter was 1.12–1.31 times that of denuded filter when using the reflectance correction. The OC to EC ratios calculated by results from the transmittance correction showed more significant variation comparing with those based on the reflectance correction; and no correlation between them was found. SOA concentrations were predicted by the EC-tracer method to investigate effects of the charring correction methods. Estimated SOA based on the reflectance correction was found to be much lower comparing with that calculated by results from the transmittance correction. SOA based on the reflectance correction might be unreliable because it exhibited no correlation with water-soluble organic carbon (WSOC). On the other hand, WSOC and SOA based on the transmittance correction correlated well ( R2 = 0.77–0.94), indicating the secondary nature of WSOC in Beijing.Display Omitted► Positive artifact would increase the ambient OC to EC ratio by 14–36%. ► Charring correction method also has substantial influence on the OC to EC ratio. ► SOA predicted by the reflectance-defined OC and EC values seems unreliable.
Keywords: Positive artifact; Thermal–optical reflectance; Thermal–optical transmittance; Secondary organic aerosol; Water-soluble organic carbon
Global time trends in PAH emissions from motor vehicles by Huizhong Shen; Shu Tao; Rong Wang; Bin Wang; Guofeng Shen; Wei Li; Shenshen Su; Ye Huang; Xilong Wang; Wenxin Liu; Bengang Li; Kang Sun (pp. 2067-2073).
Emission from motor vehicles is the most important source of polycyclic aromatic hydrocarbons (PAHs) in urban areas. Emission factors of individual PAHs for motor vehicles reported in the literature varied 4 to 5 orders of magnitude, leading to high uncertainty in emission inventory. In this study, key factors affecting emission factors of PAHs (EFPAH) for motor vehicles were evaluated quantitatively based on thousands of EFPAH measured in 16 countries for over 50 years. The result was used to develop a global emission inventory of PAHs from motor vehicles. It was found that country and vehicle model year are the most important factors affecting EFPAH, which can be quantified using a monovariate regression model with per capita gross domestic production (purchasing power parity) as a sole independent variable. On average, 29% of variation in log-transformed EFPAH could be explained by the model, which was equivalent to 90% reduction in overall uncertainty on arithmetic scale. The model was used to predict EFPAH and subsequently PAH emissions from motor vehicles for various countries in the world during a period from 1971 to 2030. It was estimated that the global emission reached its peak value of approximate 101 Gg in 1978 and decreased afterwards due to emission control in developed countries. The annual emission picked up again since 1990 owing to accelerated energy consumption in China and other developing countries. With more and more rigid control measures taken in the developing world, global emission of PAHs is currently passing its second peak. It was predicted that the emission would decrease from 77 Gg in 2010 to 42 Gg in 2030.► Measured PAH emission factors for motor vehicles varied 3–4 orders of magnitude. ► A model was developed to predict PAH emission factors based on per capita GDP. ► Overall uncertainty of the emission factors were reduced by a order of magnitude. ► World motor vehicle PAH emissions from 1970 to 2030 were predicted.
Keywords: Polycyclic aromatic hydrocarbons (PAHs); Emission factor; Vehicle emission; Global inventory; Time trend
Experimental studies on the heterogeneous reaction of NO3 radicals with suspended carbaryl particles by Bo Yang; Junwang Meng; Yang Zhang; Changgeng Liu; Jie Gan; Jinian Shu (pp. 2074-2079).
Carbaryl, a widely used pesticide, can be released into atmosphere in the gas phase and condensed phase, but its atmospheric fate is not yet well understood. In this study, the reaction between suspended carbaryl particles and NO3 radicals is investigated, and the sequential nitration of carbaryl is observed in real time with a vacuum ultraviolet photoionization aerosol time-of-flight mass spectrometer (VUV-ATOFMS). Four nitro- and/or hydroxy-substituted products are detected, which are different from degradation products of carbaryl in aqueous environments. The apparent reaction rate of particulate carbaryl with NO3 radicals is measured by a relative rate method. The decays of carbaryl and the reference compound isoprene are synchronously monitored online with VUV-ATOFMS and an atmospheric gas analysis mass spectrometer. The apparent reaction rate of condensed-phase carbaryl with NO3 radicals under experimental conditions is 4.4 × 10−13 cm3 molecule−1 s−1, which corresponds to an approximate lifetime of 1.3 h in the atmosphere for the same particle surface area and carbaryl coating as used in the experiments.► Primary & secondary oxidations of carbaryl particles by NO3 radicals are observed. ► Four nitro- and/or hydroxy-substituted products are sequentially detected. ► Carbaryl particles and the reference gas are synchronously online monitored. ► Apparent reactive rate of carbaryl particles with NO3 radicals is obtained.
Keywords: Carbaryl; NO; 3; radical; Heterogeneous reaction; Aerosol mass spectrometry
Using continuous sampling to examine the distribution of traffic related air pollution in proximity to a major road by Kim McAdam; Peter Steer; Kim Perrotta (pp. 2080-2086).
A study to characterize the distribution of vehicle related air pollution in proximity to a major arterial road was undertaken to inform local land use planning and policy regarding separation distances that could help reduce exposure for new sensitive land use development. Measurements of criteria air contaminants were made at ground level, 10 m, 30 m, and 60 m from curb side, and at 9 m height, 10 m from curb side along a traffic corridor carrying over 34,000 vehicles per day. Pollutant decay with distance or height was not statistically significant for O3, CO, or SO2. No clear distance decay pattern emerged for PM2.5. Compared to concentrations at ground level 30 m from curb side, concentrations at 10 m, 60 m, and 10 m at 9 m height were 83%, 45% and 54% higher, respectively. For NO, NO2, and NO x, however, there was a statistically significant decline in concentrations with distance with the decay most apparent from 30 m to 60 m from the road. Concentrations at 10 m from curb side at 9 m height were equivalent to (all wind conditions) or less than (downwind conditions) those at 30 m and ground level. These findings suggest that for protection of public health in the near road environment, vertical distance is an important determinant of exposure to pollutants that are key indicators of traffic related air pollution. This has implications for sensitive land use development in proximity to high volume traffic corridors.► Near road pollution decay in vertical and horizontal directions was examined. ► Decay at distance or height was not statistically significant for O3, CO, or SO2. ► No clear distance or height decay pattern emerged for PM2.5. ► For N species there was a significant decline in concentrations with distance. ► For N species, concentrations at height were similar or lower than at ground level.
Keywords: Traffic corridor; Air pollution; Distance decay; Public health; Halton Region
Characterization of PM2.5 collected during broadcast and slash-pile prescribed burns of predominately ponderosa pine forests in northern Arizona by Marin S. Robinson; Min Zhao; Lindsay Zack; Christine Brindley; Lillian Portz; Matthew Quarterman; Xiufen Long; Pierre Herckes (pp. 2087-2094).
Prescribed burning, in combination with mechanical thinning, is a successful method for reducing heavy fuel loads from forest floors and thereby lowering the risk of catastrophic wildfire. However, an undesirable consequence of managed fire is the production of fine particulate matter or PM2.5 (particles ≤2.5 μm in aerodynamic diameter). Wood-smoke particulate data from 21 prescribed burns are described, including results from broadcast and slash-pile burns. All PM2.5 samples were collected in situ on day 1 (ignition) or day 2. Samples were analyzed for mass, polycyclic aromatic hydrocarbons (PAHs), inorganic elements, organic carbon (OC), and elemental carbon (EC). Results were characteristic of low-intensity, smoldering fires. PM2.5 concentrations varied from 523 to 8357 μg m−3 and were higher on day 1. PAH weight percents (19 PAHs) were higher in slash-pile burns (0.21 ± 0.08% OC) than broadcast burns (0.07 ± 0.03% OC). The major elements were K, Cl, S, and Si. OC and EC values averaged 66 ± 7 and 2.8 ± 1.4% PM2.5, respectively, for all burns studied, in good agreement with literature values for smoldering fires.► PM2.5 was collected during broadcast and slash-pile prescribed burns. ► Samples were collected in situ. ► 19 PAHs were detected with higher levels in slash-pile burns. ► Elemental carbon levels were low, consistent with low-intensity, smoldering fires.
Keywords: Elemental carbon; Fine particulate matter; Organic carbon; PM; 2.5; Polycyclic aromatic hydrocarbons; Prescribed burn; Wood-smoke particulate
Measurements of personal exposure to NO2 and modelling using ambient concentrations and activity data by William Physick; Jennifer Powell; Martin Cope; Kate Boast; Sunhee Lee (pp. 2095-2102).
This study was undertaken with the aim of estimating true personal exposures from data that are less costly and more easily obtained than in detailed measurement programs. We present an evaluation of simple methodologies for estimating true personal exposure to nitrogen dioxide (NO2) that take into account spatiotemporal variability in ambient concentrations across urban areas and which link the latter to personal exposure through indoor/outdoor (I/O) ratios determined from time-activity diaries. To allow us to both develop and evaluate the methods, we designed a measurement program involving volunteers across Melbourne wearing personal passive samplers. Three methods of estimating indoor–outdoor ratios and three approaches to calculating ambient exposure, including network monitors and the complex air quality model TAPM-CTM, were evaluated. All methods except one produced good agreement with the measured values. Importantly, the percentile statistics and standard deviations predicted by these spatial-variation techniques matched well the distribution seen in the measurements. For the best estimates of personal exposure to NO2, it is recommended that the I/O ratio be calculated using a mass balance method, requiring participants to record daily gas cooking periods and approximate house age. The recommended method for calculating the required ambient outdoor concentration is to use values from the network monitor nearest to a person’s microenvironment. Our research has identified a simple exposure methodology that could be widely applied for epidemiological cohort studies and population exposure estimates in urban areas with fixed monitoring networks, with only minimum information from respondents.► Simple exposure methodology that could be applied for epidemiological cohort studies. ► Model links personal exposure to ambient concentration via indoor/outdoor ratios. ► I/O ratio calculated using a mass balance method. ► Ambient concentrations from nearest monitor to home or work sites.
Keywords: Personal exposure; Nitrogen dioxide; Spatiotemporal variability; Exposure modelling; TAPM-CTM; Activity data
Predicting the frequency of occurrence of visible water vapour plumes at proposed industrial sites by Andrew Sturman; Peyman Zawar-Reza (pp. 2103-2109).
Although they may have no direct health impacts, visible water vapour plumes can be of concern to the local population in the vicinity of major industrial plant developments. In this paper, prediction of the occurrence of visible plumes at proposed industrial sites is assessed using the case study of a planned major cement plant in New Zealand. The aim of the investigation was to use a simple but robust approach to estimate the frequency of occurrence of visible water vapour plumes emitted by a proposed plant, as well as their likely dimensions. Input data consisted of information relating to the raw materials used in the production process, as well as stack design parameters. The atmospheric mesoscale model TAPM (The Air Pollution Model) was run for the whole of 2007 to predict ambient conditions in the vicinity of the site. A simple model was then applied to predict visible water vapour plume development under a range of emission rates for the whole year, as well as by season. Predictions were provided for the whole year, allowing for the fact that visible plumes would not be a problem at night and during rain. Model results showed that with three different emission rates (design, intermediate and worst-case) the occurrence of visible plumes at the proposed stack site is likely to be infrequent (less than 0.1% of hours per annum at 20 m from the stack under design conditions). When they do occur, the plumes are expected to be relatively small (a few tens of metres in length/diameter). Visible plume occurrence in winter is predicted to increase to almost 0.2% of the time under the design emission rate of 8.6 kg s−1. The main effect is expected to be on visible plume development within 50 m of the stack, while further away from the stack any visible plume development is expected to be negligible. The sensitivity of visible plume development to varying stack water discharge rates is investigated, along with the specific meteorological conditions under which visible plumes are predicted to develop.► New integrated approach predicts occurrence of visible water vapour plumes. ► TAPM used to predict 3-D ambient atmospheric conditions for visible plume predictions. ► Occurrence of visible plumes predicted for whole of 2007 at proposed industrial site. ► Visible plume occurrence negligible (<0.1% of hours) under design operating conditions. ► Seasonal/diurnal variation in visible plumes occurs under moderate to extreme conditions.
Keywords: Visible water vapour plumes; TAPM; Model application; Industrial stack
Black carbon transport to a remote mountaintop in the northeastern US and relationship with other pollutants by Vincent A. Dutkiewicz; Liaquat Husain; Utpal K. Roychowdhury; Kenneth L. Demerjian (pp. 2110-2119).
We report Aethalometer black carbon (BC) measurements carried out at 15-min intervals over 30 months at a mountaintop site in northeastern New York, along with co-located measurements of CO, O3, and SO2, and high time resolved measurements of PM2.5 mass and aerosol sulfate (SO4) concentrations acquired near the base of the mountain. The mean BC concentration at the site was 84 ng m−3 while monthly means varied from 25 to 144 ng m−3. Correcting for the impact of “mountain meteorology” yields an estimated surface equivalent annual mean concentration of 100 ng m−3. Periods of episodic high BC concentrations (>300 ng m−3), however, occurred throughout the year but were longer and more intense during the warmer months. We observed that the concentrations of O3, SO2, SO4, and PM2.5 mass, and to a lesser degree CO were often highly correlated with BC concentrations during the episodes, even when air trajectories indicated that the air masses reaching the site had passed through widely varied geographical regions. We report details of three specific BC episodes and examine the relationship between the co-measured species and air trajectories.► BC concentration at Whiteface Mt. summit averaged 84 ng m−3. ► Monthly means varied from 25 to 144 ng m−3 with the highest values during summer. ► Periods of episodic high BC (>300 ng m−3), however, occurred throughout the year. ► 3 BC episodes are reported including co-measured species and air mass directions. ► Concentrations of O3, SO2, SO4, PM2.5, and CO were often highly correlated with BC.
Keywords: Carbonaceous aerosols; Black carbon; Aethalometer; Carbon monoxide; PM; 2.5; mass
Seasonal variations in aerosol characteristics over an urban location and a remote site in western India by Sumita Kedia; S. Ramachandran (pp. 2120-2128).
Spatial and temporal variabilities in aerosol optical depth (AOD) and size distribution are investigated using ground based measurements over two different locations in western India, namely, Ahmedabad (urban industrialized location) and Gurushikhar (high altitude remote site) during 2006–2008. AODs over Ahmedabad are more than two times higher than Gurushikhar at all the wavelengths indicating higher aerosol loading over Ahmedabad throughout the study period. Ångström exponent ( α) is higher over Ahmedabad than Gurushikhar suggesting higher fine mode aerosol concentration over Ahmedabad. Different values of α are observed when calculated over different wavelength ranges indicating bimodal aerosol size distribution. Discrimination of aerosol size during different seasons is made using the coefficients of polynomial fit ( α1, α2) which showed the presence of changing dominant aerosol types as a function of season over both the locations. The α2 – α1 values are used to get confirmation on the dominant aerosol mode over both the locations during different seasons. About 87% and 78% of AOD spectra are found to be dominated by wide range of fine mode fractions or mixture of modes during winter over Ahmedabad and Gurushikhar respectively. During premonsoon ≥80% of AOD spectra are found to be dominated by coarse mode aerosols over both the locations. During monsoon ∼70% of AOD spectra are coarse mode dominant over Ahmedabad. In postmonsoon <40% of AOD spectra are dominated by coarse mode aerosols over both the locations. This characterization of aerosols is important in assessing the response of different aerosol types on radiative forcing and regional climate.► Aerosol optical depths (AODs) are measured over an urban and a high altitude remote location in western India. ► AODs, and Ångström parameters ( α and β) are higher over Ahmedabad than that over Gurushikhar. ► Aerosol size distribution is found to be multimodal over both the locations. ► AOD spectra are dominated by fine mode aerosols during winter and postmonsoon. ► Coarse mode aerosols dominate during premonsoon and monsoon over both the locations.
Keywords: Aerosol optical depth; Ångström parameters; Polynomial fit; Urban and remote environment
Seasonal variation of enhancement ratios of trace gases observed over 10 years in the western North Pacific by Akira Wada; Hidekazu Matsueda; Yousuke Sawa; Kazuhiro Tsuboi; Saki Okubo (pp. 2129-2137).
We analyzed seasonal and geographical variations of the enhancement ratios of trace gases of the Asian continental pollution (ACP) events observed over the western North Pacific region. The ACP events were identified by using continuous carbon monoxide (CO) measurements taken at three monitoring stations of Minamitorishima (MNM), Yonagunijima (YON), and Ryori (RYO) in Japan for more than 10 years. The frequency of ACP events at MNM and YON increased in the winter and early spring seasons, but not at RYO. The enhanced concentrations of CO (ΔCO) associated with the ACP events showed a clear seasonal variation at MNM and YON, but not at RYO. Other trace gases of methane (CH4), carbon dioxide (CO2), and ozone (O3) were simultaneously enhanced for many of the ACP events, and were highly correlated with ΔCO. The frequency distributions of the enhancement ratios of ΔCH4/ΔCO, ΔCO/ΔCO2, and ΔO3/ΔCO depended largely on the geographical locations of the stations. Distinct seasonal variations in the enhancement ratios showed a decrease in ΔCH4/ΔCO but an increase in ΔCO/ΔCO2 in the winter and early spring at all three stations, although their seasonal amplitudes were different each station. These results indicate that the chemical compositions associated with the ACP events were considerably influenced by the seasonal variations in the trace gas emission ratios of the Asian continental source regions, with increased fluxes of CH4 in summer and CO in winter. Contributions to the ΔCH4/ΔCO and ΔCO/ΔCO2 ratios from the photochemical evolution during atmospheric transport were estimated to be not significant, while the seasonal changes in the ΔO3/ΔCO ratio were controlled significantly by the photochemistry.► Enhancement ratios of trace gases in the Asian pollution events were examined. ► We found distinct seasonal variations of CO/CO2, CH4/CO and O3/CO ratios. ► They showed large influences of seasonal flux changes in the Asia source regions.
Keywords: Asian continental outflow; Carbon monoxide; Enhancement ratio; Long-range transport; Anthropogenic emission
Air pollution exposure indicator for Greece by C. Dimitroulopoulou; V. Plemmenos; T. Kyrios; I.C. Ziomas (pp. 2138-2144).
The European Environment Agency (EEA) calculates the air pollution exposure indicator (CSI 004) for Greece using data from only one monitoring station, which is located in Athens. The present work presents an alternative approach for calculating such an indicator. This new approach is based on data from several monitoring stations in the metropolitan areas of Athens and Thessaloniki and takes into account the population living within a particular monitoring district. The assessment focuses on particulate matter (PM10), nitrogen dioxide and ozone for the period from 2001–2008. Comparisons between exposures estimated by the current procedure and those estimated by the EEA methodology indicate that the latter procedure can produce large over-estimates of exposure.
Keywords: Exposure; Regulatory exceedance indicator; PM; 10; Nitrogen dioxide; Ozone