Atmospheric Environment (v.45, #35)
Editorial board (i).
Assessing temporally and spatially resolved PM2.5 exposures for epidemiological studies using satellite aerosol optical depth measurements by Itai Kloog; Petros Koutrakis; Brent A. Coull; Hyung Joo Lee; Joel Schwartz (6267-6275).
Land use regression (LUR) models provide good estimates of spatially resolved long-term exposures, but are poor at capturing short term exposures. Satellite-derived Aerosol Optical Depth (AOD) measurements have the potential to provide spatio-temporally resolved predictions of both long and short term exposures, but previous studies have generally showed relatively low predictive power. Our objective was to extend our previous work on day-specific calibrations of AOD data using ground PM2.5 measurements by incorporating commonly used LUR variables and meteorological variables, thus benefiting from both the spatial resolution from the LUR models and the spatio-temporal resolution from the satellite models. Later we use spatial smoothing to predict PM2.5 concentrations for day/locations with missing AOD measures. We used mixed models with random slopes for day to calibrate AOD data for 2000–2008 across New-England with monitored PM2.5 measurements. We then used a generalized additive mixed model with spatial smoothing to estimate PM2.5 in location–day pairs with missing AOD, using regional measured PM2.5, AOD values in neighboring cells, and land use. Finally, local (100 m) land use terms were used to model the difference between grid cell prediction and monitored value to capture very local traffic particles. Out-of-sample ten-fold cross-validation was used to quantify the accuracy of our predictions. For days with available AOD data we found high out-of-sample R 2 (mean out-of-sample R 2 = 0.830, year to year variation 0.725–0.904). For days without AOD values, our model performance was also excellent (mean out-of-sample R 2 = 0.810, year to year variation 0.692–0.887). Importantly, these R 2 are for daily, rather than monthly or yearly, values. Our model allows one to assess short term and long-term human exposures in order to investigate both the acute and chronic effects of ambient particles, respectively.► We found high out-of-sample R 2 (R 2 = 0.830). ► For days without AOD values, we also found high R 2 (R 2 = 0.810). ► Importantly, these R 2 are for daily, rather than monthly or yearly, values. ► Our model allows to assess both short- and long-term human exposures concurrently.
Keywords: Air pollution; Aerosol optical depth; Epidemiology; PM2.5; Exposure error;
A system for free-air ozone concentration elevation with rice and wheat: Control performance and ozone exposure regime by Haoye Tang; Gang Liu; Yong Han; Jianguo Zhu; Kazuhiko Kobayashi (6276-6282).
A system for free-air concentration enrichment with ozone (FACE-O3) was installed in a field in Jiangsu Province of China to grow wheat and rice plants in either ambient [O3] (A-O3) or elevated [O3] (E-O3) without any enclosures. Ozone generated from pure O2 and mixed with compressed air was released into the E-O3 plots from a 14 m diameter octagon. The gas release was controlled for each E-O3 plot with an algorithm based on wind direction, wind speed and [O3] at the center of the plot. With 1-min mean [O3], the achieved elevation was within ±20% of the target, which is 50% above A-O3, for 94% of time, and within ±10% of the target for 73% of time on average across 4 years from 2007 to 2010. Ozone fumigation ran on daytime, but was withheld when ambient [O3] was below 20 ppb or leaves were wet. The discontinuity in O3 release resulted in the daily mean 7 h [O3] (M7, 900–1600 h Chinese Standard Time) in E-O3 by only 24% higher than that in A-O3. The average effective increase in AOT40 (accumulated [O3] above the threshold of 40 ppb) was 115%. Ozone exposure regime in E-O3 as characterized by M7 and AOT40 was compared with that in a scaled-up [O3] (S-O3), which was obtained by scaling A-O3 by 1.24: the ratio of M7 in E-O3 to that in A-O3. For the same M7, E-O3 had higher AOT40 than S-O3, because E-O3 had more high [O3] peaks than S-O3. The shift in AOT40 is only modest, however, and the [O3] regime in E-O3 was consistent with that in open-top chamber experiments in the past. This FACE-O3 system can thus maintain elevated [O3] in open field with modest alteration to [O3] regime to an extent comparable to open-top chambers.► We examined control performance and O3 concentration regime in a FACE-ozone system. ► Control performance was comparable to or better than that in other systems. ► O3 concentration regime in FACE-ozone system was peakier than that in ambient air. ► The change in O3 regime could introduce small bias in crop yield loss estimation.
Keywords: Ozone; FACE; Rice; Wheat; Ozone dose metrics; Open-top chamber;
Long-term trends of total ozone column over the Iberian Peninsula for the period 1979–2008 by M. Antón; D. Bortoli; P.S. Kulkarni; M.J. Costa; A.F. Domingues; D. Loyola; A.M. Silva; L. Alados-Arboledas (6283-6290).
The objective of this work is to analyze the total ozone column (TOC) trends over the Iberian Peninsula during the last 30 years (1979–2008). This study is carried out using TOC data derived from the Multi Sensor Reanalysis (MSR), Total Ozone Mapping Spectrometer (TOMS) and Global Ozone Monitoring Experiment (GOME). The analysis of the long-term ozone trends is focused on two sub-periods (1979–1994 and 1995–2008) in order to detect changes in the ozone trend pattern. The results show that the ozone depletion was statistically significant at the 95% confidence level during the first sub-period (1979–1994) in the entire region of study (except in the Southerner locations), with linear trends from −4.5%/decade to −2.5%/decade. These linear trends present a clear dependence on latitude, being higher for the Northerner locations than for the Southerner. By contrast, the analysis of the second sub-period of study (1995–2008) shows positive ozone trends over the Iberian Peninsula, with the highest values (+2.5%/decade) in the Northeast of this region. This result indicates that the ozone layer may be responding as expected to the controls on ozone-depleting substances imposed by the Montreal Protocol. Additionally, a seasonal trend analysis is performed using the average of the deseasonalized monthly values for each season of the year. The seasonal analysis showed that the negative ozone trends during the first sub-period of study were statistically significant in the spring and winter, while that the seasonal ozone trends obtained during the second sub-period are positive but in general not significant at 95%.► The ozone depletion was significant for the periods 1979–1994 and 1979–2008. ► The period 1995–2008 showed a positive ozone trend. ► Ozone trends (1979–1994 and 1979–2008) showed clear dependence on latitude.
Keywords: Total ozone column; Trend; TOMS; GOME; Iberian Peninsula;
Evaporation in relation to CO2 concentration: Analysis of mass transfer coefficient by C.S.P. Ojha; Hiroshi Yasuda; Surampalli Rao; Mohamed A.M. Abd Elbasit; Manoj Kumar (6291-6298).
In this study, the potential of mass transfer approach in estimating evaporation changes under different CO2 levels are evaluated using data from controlled chamber experiments in which radiation and wind velocity were kept constant and temperature and relative humidity profiles were varied in different patterns along with CO2 concentration. Currently, FAO procedure lists three approaches to compute air vapour pressure based on temperature and relative humidity profiles. In this study, the impact of using different procedures of estimating air vapour pressure is examined to assess the use of mass transfer approach for estimating evaporation. To achieve this, a part of the data is used to calibrate mass transfer coefficient which is subsequently used to project evaporation for future states. Accordingly, strategies are ranked for their potential in estimating evaporation. The effect of evaporation rate is compared at 400 ppm and 600 ppm CO2 level. It has been observed that the evaporation rate is more pronounced at higher CO2 level.► The evaporation at 600 ppm CO2 concentration is higher than at 400 ppm. ► Mass transfer approach is a potential estimator of evaporation. ► Several strategies are evaluated to estimate the mass transfer coefficient. ► Best performing strategy is identified.
Keywords: Evaporation; Mass transfer; Vapour pressure; Relative humidity; Temperature; Carbon-di-oxide concentration;
Annual sulfur deposition through fog, wet and dry deposition in the Kinki Region of Japan by Hikari Shimadera; Akira Kondo; Kundan Lal Shrestha; Akikazu Kaga; Yoshio Inoue (6299-6308).
This study estimated annual sulfur (SO2 + SO4 2−) deposition through fog, wet and dry deposition in the Kinki Region of Japan from April 2004 to March 2005. The numerical models used in this study include the Weather Research and Forecasting model (WRF), the Community Multiscale Air Quality model (CMAQ), and a fog deposition model. WRF well predicted mountain fog at Mt. Rokko, the meteorology near the ground surface in the Kinki Region and the upper air meteorology in Japan during the simulation period. CMAQ well predicted the long-range atmospheric transport of aerosol SO4 2− from the Asian Continent to Japan. The mean SO4 2− concentration in fog water was approximately 6 times higher than that in precipitation in the Kinki Region. Ratios of fog water deposition to precipitation reached up to more than 10% in some mountainous areas in the Kinki Region. Consequently, the amount of sulfur deposition through fog water deposition was larger than that through dry deposition and comparable to that through wet deposition in some mountainous areas in the Kinki Region.► We estimated sulfur deposition through fog, wet and dry deposition in Kinki Region. ► WRF/CMAQ well simulated the meteorology and air quality. ► SO4 2− concentration in fog water was 6 times higher than that in precipitation. ► Fog water deposition was large in the mountainous areas with high fog frequency. ► Fog water deposition is important in some mountains in Kinki Region of Japan.
Keywords: Fog deposition; Acid deposition; Transboundary air pollution; WRF/CMAQ; Fog water deposition model;
Inorganic ion and nitrogen isotopic compositions of atmospheric aerosols at Yurihonjo, Japan: Implications for nitrogen sources by Hiroto Kawashima; Takahiro Kurahashi (6309-6316).
We studied the suspended particulate matter (SPM) collected in Akita Prefecture, Japan from April 2008 to January 2009 for inorganic ion composition and nitrogen isotopic ratio (δ 15N) of NH4 + and NO3 −. The results showed an average SPM concentration of 15.6 μg m−3. The seasonal trend for SPM was higher values in the spring, lower in the winter. The major cations were Na+, NH4 +, Ca2+ and major anions were SO4 2−, NO3 −, Cl−. The annual correlation coefficient of ions indicates a very high value with NH4 + and SO4 2− (R = 0.93), NO3 − and K+ (R = 0.65), NO3 − and Ca2+ (R = 0.62). The high springtime values are the apparent result of the dust stream from Asia. Average δ 15N–NH4 + and δ 15N–NO3 − were 16.1‰ and −0.69‰, respectively. δ 15N–NH4 + increased slightly in summer, and δ 15N–NO3 − increased considerably in winter. The trends indicated conversely. The heavy δ 15N–NH4 + in summer appears to be from agricultural sources such as animal waste and fertilizer. In addition, according to the difference in isotopes of NO x sources as the precursor of NO3 −, the dominant origin of heavy δ 15N–NO3 − in winter could be NO x emitted from fossil fuel combustion at low temperature. Moreover, the average δ 15N–NO3 − seemed to be made to baseline (approximately 0%) by vehicle emissions at high temperature. These results are considered to be very reasonable.► We investigated ammonium and nitrate source in aerosol to use nitrogen isotope. ► Stable nitrogen isotope ratio of ammonium and nitrate for long range were analyzed. ► Nitrate in winter seemed to be affected a long-range effect of coal combustion.
Keywords: Stable nitrogen isotope ratio; Suspended particulate matter; Nitrate; Ammonium ion;
Trends in aerosol optical properties over the Bohai Rim in Northeast China from 2004 to 2010 by Jinyuan Xin; LiLi Wang; Yuesi Wang; Zhanqing Li; Pucai Wang (6317-6325).
Strong seasonal variations in regional aerosol optical depth at 550 nm (AOD) and aerosol type were investigated over China’s Bohai Rim based upon six years’ worth of data from four sites. Aerosol loading was higher and particle sizes were larger in the spring and summer than in the autumn or winter in the region. The regional mean background AOD and Angstrom exponent (α) were 0.20 ± 0.03 and 0.74 ± 0.17, respectively, and these values decreased by roughly 0.01 and 0.40 over the past six years. The annual mean AOD and α were 0.50 ± 0.06 and 1.09 ± 0.23 at three typical observation stations in the Bohai Rim economic zone. AOD increased by 0.07 and α decreased by 0.18 over the past six years, presumably due to rapid economic growth in the special zone. The accuracy of the MODIS C051 AOD product was relatively low over this region, and 52% of MODIS AOD product was within the expected error. The averaged standard deviation between annual mean ground-based and MODIS retrievals of AOD was ±0.11, but the monthly mean and seasonal mean differences ranged from −0.34 to +0.45 and from −0.17 to +0.24, respectively, at the four sites studied. The calibrated MODIS AOD was adjusted by the seasonal liner regression functions between daily ground-observed AOD and raw MODIS AOD product. The averaged standard deviations of the calibrated MODIS AOD values were ±0.02 for the annual means and ±0.08 for the monthly means. The accuracy of the calibrated MODIS AOD was found to be reliable.► There was a “dimming” trend in AOD in the Bohai Rim, the third largest economic zone in China. ► There was a “slight brightening” trend in the regional background AOD over the past six years. ► Retrieval differences of MODIS AOD can be further propagated when deriving the monthly mean. ► Calibrated by the ground observation, the accuracy of MODIS AOD was reliable.
Keywords: Aerosol optical depth; Angstrom wavelength exponent; MODIS; Seasonal variation;
Organic-rich nanoparticles (diameter: 10–30 nm) in diesel exhaust: Fuel and oil contribution based on chemical composition by Akihiro Fushimi; Katsumi Saitoh; Yuji Fujitani; Shuichi Hasegawa; Katsuyuki Takahashi; Kiyoshi Tanabe; Shinji Kobayashi (6326-6336).
The size distribution of particle number concentrations and comprehensive chemical composition (elemental and organic carbon, elements, ions, and organic compounds) by particle size (diameter: 0.010–10 μm) were measured under no-load and transient conditions in the exhaust from an 8-L diesel engine with no exhaust after-treatment system and from a 3-L diesel vehicle equipped with an oxidation catalyst. High concentrations of nuclei-mode particles were emitted from the 8-L engine under no-load condition (8L-NoLoad), even when low-sulfur (8 ppm) fuel was used, but no nuclei-mode particles were emitted from the 3-L vehicle. Organic carbon accounted for a major part (79–80%) of the measured components of the nanoparticles (diameter: 10–32 nm) under 8L-NoLoad, but elemental carbon accounted for only 8–15%; elements and ions including sulfate accounted for only small percentages. The mass chromatogram (m/z 85) patterns obtained by gas chromatography–mass spectrometry of the nanoparticles were similar to those for lubricating oil, and the peak profiles for hopanes were equivalent to those in oil. The 17α(H),21β(H)-hopane concentrations per particle mass were higher in smaller particles. The elements concentrated in oil were also concentrated in the nanoparticles. These results suggest that not sulfate and fuel but organics derived from oil were the primary components of the nanoparticles under 8L-NoLoad. From the 17α(H),21β(H)-hopane concentrations, the oil contribution to the sum of measured components in the nanoparticles under 8L-NoLoad was estimated at 79–92%. Comparable oil contributions were estimated from Ca and Zn concentrations.► Comprehensive chemical composition of diesel exhaust nanoparticles was measured. ► Organics were dominant for the nanoparticles under nanoparticle-dominated condition. ► Oil contribution in the organic-rich nanoparticles was estimated at 79–92%.
Keywords: EC/OC; Organic compounds; Elements; Ions; Nuclei-mode particles;
Dependence of aerosol–cloud interactions in stratocumulus clouds on liquid-water path by S.S. Lee; J.E. Penner (6337-6346).
A recent study showed that aerosol-induced feedbacks between microphysics and dynamics predominantly determined the cloud-mass response to aerosols in thin clouds with liquid-water path (LWP) of ∼50 g m−2 or less; in this paper, cloud mass represents the time- and area-averaged LWP and LWP is the column-integrated cloud liquid content (LWC); LWC is the mass of cloud liquid per unit volume of air. This is contrary to studies which have shown that aerosol-induced inefficient conversion and sedimentation play an important role in the determination of the effect of aerosols on cloud mass. These studies are generally based on clouds with LWP >50 g m−2. Hence, it is important to understand whether the role of aerosol-induced feedbacks in the effect of aerosols on cloud mass depends on the level of LWP. Pairs of numerical experiments for high and low-aerosol cases are run for four cases of stratiform clouds with different LWPs. All of these cases show that the role of condensation or evaporation of cloud liquid in the cloud-mass response to aerosol is more important than that of conversion of cloud liquid to rain and sedimentation (or precipitation). This indicates that focusing only on parameterization of autoconversion and sedimentation to represent aerosol effects on cloud mass in climate models can be misleading. Also, this study finds that the effect of aerosol-induced sedimentation suppression on the cloud-mass response to aerosol becomes less important as LWP lowers. Instead, the effect of aerosol-induced changes in condensation or evaporation on the cloud-mass response becomes more important with the decreasing LWP. These changes in condensation (and associated changes in evaporation) are caused by interactions (or feedbacks) among aerosol, droplet surface area, supersaturation, and instability around cloud base.► Wide variation of role of sedimentation in aerosol effect on cloud mass with LWP. ► Important role of feedbacks between microphysics and dynamics in the variation. ► Consideration of the feedbacks for correct assessment of aerosol effect on cloud.
Keywords: Aerosol; Stratocumulus clouds; Condensation; Liquid-water path;
Verification of anthropogenic emissions of China by satellite and ground observations by Shuxiao Wang; Jia Xing; Satoru Chatani; Jiming Hao; Zbigniew Klimont; Janusz Cofala; Markus Amann (6347-6358).
An integrated emission inventory of China was validated through comparing the Community Multi-scale Air Quality (CMAQ) simulations with the NO2 and SO2 column retrieved from Ozone Monitoring Instrument (OMI), Aerosol Optical Depth (AOD) retrieved from Moderate Resolution Imaging Spectroradiometer (MODIS), and ground observations of SO2, NO2, PM10, PM2.5 and its components. The model simulations were performed for year 2005. The model generally reproduces both spatial distribution and seasonal variation of tropospheric NO2, SO2 column densities and AOD in China that have been observed by OMI and MODIS. The correlation coefficients between model simulated and satellite observed NO2 column densities, SO2 column densities and AOD over east China are 0.90, 0.85 and 0.79, and the normalized mean bias (NMBs) are −8%, 1%, and −8% respectively, which are comparable with the errors from satellite retrievals. The surface concentrations of NO2, SO2, and PM10 given by CMAQ model are also comparable with those observed in Beijing, Shanghai, and Guangzhou, with the NMBs ranging from 1% to 18%, −3% to −25%, and −12% to 18%, respectively. The results suggest that the anthropogenic emissions of SO2, NOx, and PM10 used in this study are in line with both the satellite and ground observations therefore are of acceptable accuracy. There is overestimation for SO2 and underestimation for PM10 in some industry-intensive areas because of the inaccuracy of spatial and temporal allocations. The CMAQ model also significantly underestimates the PM2.5 concentration in Beijhjing, mainly due to the limitation of secondary organic aerosol (SOA) formation mechanism used in the model and the underestimation of primary OC and EC emissions. Therefore more efforts shall be made to improve the primary emission estimates of OC and EC, as well as the temporal allocation factor of SO2 and PM10 emissions.► An integrated emission inventory was established for China in 2005. ► CMAQ model can reproduce spatial and seasonal variations of SO2, NO2 and PM. ► Emissions of organic carbon and elemental carbon emissions are underestimated. ► The temporal allocation factor of SO2 and PM10 emissions needs to be improved.
Keywords: Emission inventory; CMAQ simulation; Column density; Satellite; China;
Indoor and outdoor sources and infiltration processes of PM1 and black carbon in an urban environment by M. Viana; S. Díez; C. Reche (6359-6367).
Ambient air emissions of sub-micron particles infiltrate into indoor environments and play a major role in indoor air quality. Discriminating between particles of indoor vs. outdoor origin is therefore essential when assessing indoor air pollutant levels and characteristics. Outdoor/indoor relationships of traffic-derived nanoscaled particulates (PM1 and black carbon) were determined in a typical Mediterranean environment. Results evidenced the major impact of outdoor vehicular traffic emissions on indoor particulates: despite windows remaining closed at all times, 70% of indoor BC and 73% of indoor PM1 originated from outdoor emissions. This was probably due to due to inadequate insulation of the building. Outdoor/indoor penetration ratios were relatively constant for BC (1.29 ± 0.08) but not for PM1 (1.95 ± 0.38), suggesting it is advisable to monitor the variability of penetration factors over time. Particle infiltration seemed to depend not only on physical barriers (building envelope, ventilation systems, etc.), but also on the physico-chemical properties of the particulates. Printing and photocopying contributed with 25–30% (546 ng m−3) of total indoor BC. Dust re-suspension by worker passage was the main indoor source of PM1 (15–20%, 1.1 μg m−3).► We assess the impact of outdoor particle emissions on indoor air quality. ► We examine sub-micron particulates: PM1 and black carbon (BC). ► 70% of indoor BC and 73% of indoor PM1 originated from outdoor emissions. ► Outdoor/indoor penetration ratios vary with time and should be monitored. ► Printing/copying and dust re-suspension are the main indoor sources of BC and PM1.
Keywords: Exhaust; Infiltration; Penetration ratio; Barcelona; Spain; Shift analysis;
Global sand and dust storms in 2008: Observation and HYSPLIT model verification by Yaqiang Wang; Ariel F. Stein; Roland R. Draxler; Jesús D. de la Rosa; Xiaoye Zhang (6368-6381).
The HYSPLIT model has been applied to simulate the global dust distribution for 2008 using two different dust emission schemes. The first one assumes that emissions could occur from any land-use grid cell defined in the model as desert. The second emission approach uses an empirically derived algorithm based on satellite observations. To investigate the dust storm features and verify the model performance, a global dataset of Integrated Surface Hourly (ISH) observations has been analyzed to map the spatial distribution and seasonal variation of sand and dust storms. Furthermore, the PM10 concentration data at four stations in Northern China and two stations in Southern Spain, and the AOD data from a station located at the center of the Sahara Desert have been compared with the model results. The spatial distribution of observed dust storm frequency from ISH shows the known high frequency areas located in North Africa, the Middle East, Mongolia and Northwestern China. Some sand and dust storms have also been observed in Australia, Mexico, Argentina, and other sites in South America. Most of the dust events in East Asia occur in the spring, however this seasonal feature is not so evident in other dust source regions. In general, the model reproduces the dust storm frequency for most of the regions for the two emission approaches. Also, a good quantitative performance is achieved at the ground stations in Southern Spain and Western China when using the desert land-use based emissions, although HYSPLIT overestimates the dust concentration at downwind areas of East Asia and underestimates the column in the center of the Saharan Desert. On the other hand, the satellite based emission approach improves the dust forecast performance in the Sahara, but underestimates the dust concentrations in East Asia.► Two dust emission schemes are used in HYSPLIT to simulate the global dust distribution for 2008. ► A global dataset of surface and satellite data is analyzed and compared with the model. ► The model reproduces the dust storm frequency for most of the regions for the two emission approaches.
Keywords: Sand and dust storm; Observation; HYSPLIT model; Verification;
Mapping aerosol intrusion in Himalayan valleys using the Moderate Resolution Imaging Spectroradiometer (MODIS) and Cloud–Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) by Julien Brun; Prabhakar Shrestha; Ana P. Barros (6382-6392).
Mapping the spatial and temporal distribution of aerosols along mountain ranges is an important step toward elucidating orographic aerosol–cloud–rainfall interactions. This requires high spatial resolution aerosol observations over complex topography, which are not currently available either from ground-based observing systems or from remote-sensing products. Here, a novel approach is presented that relies on visible channels from MODIS Rapid Response data at 250 m spatial resolution to extract the daytime aerosol run-up (intrusion length and height) from the Indo-Gangetic Plains to the High Himalaya. Intrusion length and height are determined from the intersection of topography with the MODIS-derived aerosol plume using an adaptive object-classification algorithm. The methodology is demonstrated for a case study of the Arun River in eastern Nepal. Results of run-up extraction are examined along with the Total Attenuated Backscatter (Level 1B at 532 nm) from CALIPSO to investigate the regional variability of aerosol. During the pre-monsoon season, CALIPSO nighttime profiles show the presence of a slanted dust layer following the envelope topography. This is consistent with upper level transport of aerosol by north-westerly winds associated with high-frequency dust storms. In the winter, the signal is weaker, and the nighttime elevated aerosol layer is flat and remains below the envelope orography consistent with blocking conditions. For both seasons, the daytime aerosol layer detected from MODIS observations is always below the ridges. This suggests that in addition to seasonal variability governed by synoptic conditions, there is a distinct diurnal cycle in the North–South transport of aerosol between the Himalayas and the IGP.► High-resolution mapping of aerosol plumes in mountainous regions. ► Aerosol run-up (intrusion length and plume depth) in deep Himalayan valleys. ► Remote-sensing technique using MODIS RR and CALIPSO TBA data. ► Pre-monsoon nocturnal aerosol transport elevated above orography, blocked in winter. ► Diurnal cycle impacted by local sources, governed by mountain-valley circulations.
Keywords: Aerosol; Intrusion; River valley; High resolution; MODIS; CALIPSO; Nepal;
Thermal evolution of diffusive transport of atmospheric halocarbons through artificial sea–ice by M.D. Shaw; L.J. Carpenter; M.T. Baeza-Romero; A.V. Jackson (6393-6402).
Diffusion through brine channels in sea–ice is a potential pathway for trace gases produced under and within sea–ice to exchange with the overlying atmosphere. The effectiveness of this transport pathway is highly dependent on temperature and sea–ice thickness, both of which are changing in favour of increased gas diffusion through porous sea–ice. We conducted several experiments with artificial sea–ice in a cold chamber to assess the potential for dissolved gaseous halocarbons to percolate through brine channels within sea–ice to the overlying air. Physico-chemical properties of the hyper-saline brine, sea–ice and the under-lying seawater were measured to quantify the vertical transport of a comprehensive range of volatile organic iodinated compounds (VOICs), including CH3I, C2H5I, 2-C3H7I and 1-C3H7I, at air temperatures of −3 and −14 °C. We find that the vertical transport of VOICs through sea–ice provides a very small flux pathway for gas transport during periods of consolidated ice cover. The results suggest that VOIC gas transfer velocities from diffusion through the sea–ice alone are at least ∼60 times lower at −3 °C than gas exchange from leads and polynas during the winter (assuming a sea–ice fractional coverage of 0.1). Assuming 100% brine channel fractional connectivity and a diffusion coefficient (D) of 5 × 10−5 cm2 s−1 at −3 °C, the timescale of diffusion through 500 mm of first year sea–ice is ∼145 days. This has significant implications for in-situ VOIC losses within the brine from chlorination, hydrolysis and photolysis processes and it is unlikely that measurable concentrations of VOICs would survive vertical transport from the under-lying seawater to the surface sea–ice quasi-liquid layer.► Gas transfer velocities through sea–ice brine at −3 °C are <2% of those from leads. ► Organohalogen diffusion through 50 cm of first year sea–ice at −3 °C takes ∼145 days. ► Diffusive transport of gases through sea–ice brine offers a very small flux pathway.
Keywords: Halocarbons; Sea–ice; Brine channel; Vertical transport; Sea–ice–air flux;
Spatial distributions of ultrafine particles and their behavior and chemical composition in relation to roadside sources by Shinji Kudo; Kazuhiko Sekiguchi; Kyung Hwan Kim; Kazuhiko Sakamoto (6403-6413).
Vertical and horizontal distributions of the chemical components of ultrafine particles (UFP; <0.1 μm) in relation to roadside sources were investigated by using a newly developed PM0.1 collection system with a UFP impactor filter (50% cut-off, 0.1 μm; air flow rate, 40.0 L min−1). UFP were measured at a suburban roadside, at two background sites in Saitama (summer 2007 and winter 2008), and at two levels on a high-rise building in Tokyo (summer and winter 2005). The results from the high-rise building showed that ultrafine elemental carbon from vehicle exhaust can reach the upper atmosphere regardless of season because of the high diffusivity of UFP. The total concentrations of the carbonaceous and ionic components at all sites except the roadside site in summer were mostly within the same range. Therefore, UFP diffuse both vertically and horizontally, and its chemical components are distributed uniformly. The UFP composition in summer reflected not only the vehicle exhaust contribution but also photochemical formation, especially at the low-elevation sites, where the samplers were installed several meters above ground level. The results also showed that ionic components contributed to increases in the UFP levels.► Vertical distribution of chemical components of ultrafine particles at roadside. ► Total concentration of the carbonaceous and ionic components at non-roadside site. ► Possibility of the high diffusivity of UFP.
Keywords: Ultrafine particles; Chemical composition; Roadside; High-rise building; Spatial distribution; Photochemical formation;
Kinetics of the HO2 + NO2 Reaction: On the impact of new gas-phase kinetic data for the formation of HO2NO2 on HOx, NOx and HO2NO2 levels in the troposphere by A. Bacak; M.C. Cooke; M.W. Bardwell; M.R. McGillen; A.T. Archibald; L.G. Huey; D. Tanner; S.R. Utembe; M.E. Jenkin; R.G. Derwent; D.E. Shallcross; C.J. Percival (6414-6422).
The rate coefficient for the reaction HO2 + NO2 has been measured using a turbulent flow technique with high pressure chemical ionization mass spectrometry for the detection of reactants. The rate constant was measured between 75 and 700 Torr and at 298, 223 and 200 K. This work represents the first experimental evaluation of this rate coefficient at temperatures below 219 K. The kinetic data has been evaluated in both a global 3-dimensional atmospheric chemistry model of the troposphere and in a steady-state model. These new data improve the agreement between the steady-state model and field measurements but an unresolved discrepancy remains. Field measurements suggest that some pernitric acid may persist in the upper troposphere and if this background is taken into consideration together with these new kinetic data, good agreement between steady-state models and measurements emerge. Global model runs show that on average HO2NO2 levels are reduced by 30–40% in the upper troposphere and 20–30% in the free troposphere. This reduction in HO2NO2 leads to increases in HOx and NOx in the upper troposphere, most notably a rise of 1–12% in OH and around 5% in NOx.► In this study we measure the rate coefficient for the formation of perntiric acid in the atmosphere. ► The kinetic data has been evaluated in both a global 3-dimensional atmospheric chemistry model. ► These new data improve the agreement between the steady-state model and the field measurements. ► The data suggest that some pernitric acid may persist in the upper troposphere.
Keywords: Pernitric acid; HO2NO2; Troposphere; 3D global model; STOCHEM; CRI;
Black carbon aerosols over an urban area in south-eastern Spain: Changes detected after the 2008 economic crisis by H. Lyamani; F.J. Olmo; I. Foyo; L. Alados-Arboledas (6423-6432).
Continuous measurements of black carbon (BC) concentrations performed at Granada, an urban location in southeast Spain, using a Multi-Angle Absorption Photometer from December 2005 to November 2008, are analysed and discussed here. The daily mean BC concentrations showed considerable day-to-day variations and were found to vary from low values of 0.5 μg m−3 to high values of 8.6 μg m−3, with overall mean and standard deviation of 3.0 ± 1.5 μg m−3. The annual mean BC concentrations were similar during 2006 and 2007 (3.2 ± 1.4 μg m−3 and 3.1 ± 1.6 μg m−3, respectively), but decreased by about 16–18% to 2.6 ± 1.4 μg m−3 in 2008. This reduction is not only observed in the mean value, but also in the median, third and first quartiles. A Mann–Whitney test at 0.05 significance level confirms that the BC concentration difference between 2006 and 2007 is statistically no significant while the BC concentration in 2008 tends to be less than that in 2006–2007. Analysis of meteorological conditions suggested that although the day-to-day variations in BC concentrations were driven mostly by meteorology, the reduction in the use of fossil fuels due to economic slowdown contributed significantly to the observed decrease in BC concentrations in 2008. Under conditions dominated by local source emissions, the effect of the economic crisis on BC concentration was more pronounced. For the three analysed years, BC concentrations obtained during winter were higher than those measured during summer, probably due to increased emissions from domestic heating and less intense vertical mixing in winter season, which lead to the confinement of the BC particles near the surface. The monthly mean BC concentrations were lower in 2008 than in 2006–2007 for almost every month of the year. In all years BC concentrations exhibited a clear diurnal pattern, with two maxima and two minima within a day. There were no differences among the daily patterns for 2006, 2007 and 2008 except for a general reduction in BC concentrations on 2008, especially during morning and evening traffic hours. For every day of the week, BC concentrations were lower on 2008 than in 2006 and 2007 and this reduction was more pronounced on working days, when BC concentrations were high.► Seasonal, weekly and diurnal variation of BC in an urban area are analysed. ► BC showed high levels in winter and low levels in summer. ► Annual mean BC density decreased by 16–18% in 2008 compared to 2006–2007. ► This decrease seems to be associated to emission reductions due to economic crisis. ► BC densities showed clear diurnal and weekday cycles.
Keywords: Black carbon; Anthropogenic aerosol; Emission decline;
Measurements of atmospheric aerosols with diameters greater than 10 μm and their contribution to fixed nitrogen deposition in coastal urban environment by Kiyoshi Matsumoto; Sae Tominaga; Manabu Igawa (6433-6438).
Annual measurements of the number concentrations and chemical composition of the particles with diameters greater than 10 μm (PM>10) were conducted at a coastal urban site in Japan. The number concentrations of the PM>10 showed an annual mean of 2.14 × 103 m-3, and synchronously varied with those of the particles with diameters greater than 3 μm (PM>3). The PM>10 mainly consisted of sea-salt and soil particles. NO3 − and nss-SO4 2− were detected in the PM>10 at high concentrations. The chemical composition of the PM>10 was similar to that of the particles with diameters of 2–10 μm (PM2–10). The PM>10 would have similar sources and removal processes with the PM2–10.The dry deposition flux of the particle mass was mostly (approximately 67%) contributed by the PM>10. The PM>10 has a significant contribution to the dry deposition flux of the particulate substances. Approximately 42% of the dry deposition flux of particulate nitrate–nitrogen (NO3 −–N) was contributed by the PM>10, although only 9.5% of the NO3 −–N concentration was detected in the PM>10. During the summer period, especially, the contribution of the PM>10 to the dry deposition of the NO3 −–N increased to approximately 51%. The present study demonstrates that the PM>10 are significant carriers for NO3 −–N from the atmosphere to the earth’s surface.► The particles with d > 10 μm (PM>10) were measured in a coastal urban site. ► Annual mean number concentration of the PM>10 was 2.14 × 103 m−3. ► Contribution of the PM>10 to dry deposition flux of NO3 − was estimated to be 42 %. ► PM>10 are significant carriers for NO3 − from the atmosphere to the earth’s surface.
Keywords: Coarse particle; Number concentration; Nitrate; Fixed nitrogen; Dry deposition;
Impact of continuously varied SST on land-sea breezes and ozone concentration over south-western coast of Korea by Soon-Hwan Lee; Hwa-Woon Lee; Yoo-Keun Kim; Won-Bae Jeon; Hyun-Jung Choi; Dong-Hyuk Kim (6439-6450).
Several comparison studies including numerical experiments were carried out at the well urbanized Gwangyang Bay region, Korea, to clarify the relationship between the continuously varied SST distribution and meteorology and how that impacts the ozone concentration. The numerical models used in this study were Regional Atmospheric Modeling System (RAMS) and Comprehensive Air quality Model with eXtensions (CAMx) for meteorological and photochemical ozone fields, respectively.Based on buoy observations, the sea surface temperature (SST) had a noticeable influence on the near surface wind field and distribution of photochemical ozone because the mean SST near Gwangyang Bay changed by 2.8 °C over the five day period. Sea breeze with temporally varied SST was better represented than that estimated without the SST variation. Temporally changed SST distribution and its impact are more crucial factors for estimating the ozone concentration under weak synoptic conditions. And the accuracy of the estimated ozone concentration associated with the time varied SST tends to depend on the distance from the coastline. The acquisition of ocean conditions, including temporal variation in the SST, is indispensible for assessing and predicting the air quality, especially in well urbanized area near the coast.► We estimated the impact of continuously varied SST in coastal region. ► Sea breeze is strongly associated with continuously varied SST. ► Ozone transportation depends on the change the sea breeze behaviors. ► Influence of continuously varied SST is different for the site location.
Keywords: RAMS; CAMx; SST variation; Land-sea breezes; Ozone concentration; South-western coast of Korea;
The intrinsic fluorescence spectra of selected pollen and fungal spores by David J. O’Connor; Daniela Iacopino; David A. Healy; Daniel O’Sullivan; John R. Sodeau (6451-6458).
Primary Biological Aerosol Particles (PBAP) are ubiquitous in the atmosphere and recently the measurement of their fluorescence properties, in real-time, have been used to discriminate biological (particularly pollen and fungal spores) from non-biological particles in ambient environments. In the laboratory study reported here, the fluorescence spectra of several types of PBAP have been measured at 370 nm excitation. By this means, instructive spectroscopic signatures have been obtained for the various botanical families and orders studied here. All the spore emission spectra were shown to closely resemble each other: they display peaks at 415 nm and broad continua between 450 and 500 nm. In comparison the pollen gave discriminating spectra. For example, the Betulaceae exhibit three distinctive and virtually identical features at 420 nm, 465 nm and 560 nm. The conifers (Pinus sylvestris, Picea abies and Taxus baccata) pollen also display these features although with differing relative intensity ratios compared to the Betulaceae. Importantly, the grasses not only show the common pollen spectral features but also a sharp band at 675–680 nm: this observation demonstrates the presence of chlorophyll-a. The latter fluorescence signal could, in principle, be used in the real-time atmospheric identification of grass pollen, which are known carriers of aeroallergens. A PCA analysis was also conducted on the obtained spectra and demonstrated that grass pollen were separable from the other samples under investigation.► The fluorescence spectra of several types of PBAP have been measured. ► Spectroscopic signatures for selected botanical families/orders have been obtained. ► The pollen gave clearly discriminating emission spectra. ► The grasses show a sharp band at 675 nm demonstrating the likely presence of chlorophyll-a. ► This latter signal could be used in the real-time atmospheric identification of grass pollen.
Keywords: Fluorescence; Primary Biological Aerosol Particle;
Characterization of road dust collected in Traforo del San Bernardo highway tunnel: Fe and Mn speciation by Fabrizio Bardelli; Elti Cattaruzza; Francesco Gonella; Giancarlo Rampazzo; Gabrio Valotto (6459-6468).
X-ray Absorption Spectroscopy (XAS), X-Ray Diffraction (XRD), Thermo-Gravimetric Analysis (TGA) and Scanning Electron Microscopy–Energy Dispersive Spectroscopy (SEM–EDS) techniques were used to determine the composition and the speciation of Fe and Mn in road dust samples collected in the Traforo del San Bernardo highway tunnel. Principal Component Analysis and Least Square Fitting on the XANES region of the absorption spectra and structural refinements on the EXAFS part of the spectra were applied to obtain complementary information on the speciation, average oxidation state, and local structure of Fe and Mn. XRD indicated the presence of silica, calcite, gypsum, and of various phyllosilicates. TGA analysis confirmed the presence of phyllosilicates and also detected a significant amount of organic phases. These findings indicate the co-presence of particles of natural origin along with the organic phases related to vehicular gas exhausts emission. On the other hand, XAS analysis showed that iron is mainly present in the Fe3O4 and FeCl3 forms, which can be considered to have both anthropic origin, i.e., exhaust emission and salt used to prevent ice formation, respectively.► We use XAS, XRD, TGA, SEM–EDS techniques to probe road dust of S. Bernardo tunnel. ► Fe and Mn is found in oxide forms and/or bound to chlorine or sulfur by XAS. ► XRD reveal silica, gypsum, calcite, phyllosilicates containing Si, Mg, Na, K, Al. ► Fe and Mn oxides, sulfides, and chlorides phases are below the XRD detection limit. ► TGA reveal a significant organic component and confirm the phyllosilicate presence.
Keywords: Road dust; Fe; Mn; XAS; XRD; TGA; SEM–EDS;
Transport, vertical structure and radiative properties of dust events in southeast China determined from ground and space sensors by Jianjun Liu; Youfei Zheng; Zhanqing Li; Connor Flynn; E.J. Welton; Mareen Cribb (6469-6480).
Two dust events were detected over the Yangtze Delta region of China during March 14–17 and April 25–26 in 2009 where such dust events are uncommon. The transport behavior, spatio-temporal evolution, vertical structure, direct radiative effects, as well as induced heating rates, are investigated using a combination of ground-based and satellite-based measurements, a back-trajectory analysis, an aerosol model and a radiative transfer model. Back-trajectories, wind fields and aerosol model analyses show that the first dust originated in northern/northwestern China and the second generated in the Taklimakan desert in northwest China, and traveled across the Hexi corridor and Loess Plateau to the Yangtze Delta region (the so-called “dust corridor”). The mean lidar extinction-to-backscatter ratio (LR) during the two dust events was 38.7 ± 10.4 sr and 42.7 ± 15.2 sr, respectively. The mean aerosol depolarization ratio (δ a) for the first dust event was 0.16 ± 0.07, with a maximum value of 0.32. For the second, the mean δ a was around 0.19 ± 0.06, with a maximum value of 0.29. Aerosol extinction coefficient and δ a profiles for the two events were similar: two aerosol layers consisting of dust aerosols and a mixture of dust and anthropogenic pollution aerosols. The topmost aerosol layer is above 3.5 km. The maximum mean aerosol extinction coefficients were 0.5 km−1 and 0.54 km−1 at about 0.7 km and 1.1 km, respectively. Significant effects of cooling at the surface and heating in the atmosphere were found during these dust events. Diurnal mean shortwave radiative forcings (efficiencies) at the surface, the top-of-the-atmosphere and within the atmosphere were −36.8 (−80.0), −13.6 (−29.6) and 23.2 (50.4) W m−2, respectively, during the first dust event, and −48.2 (−70.9), −21.4 (−31.5) and 26.8 (39.4) W m−2, respectively, during the second dust event. Maximum heating rates occurred at 0.7 km during the first dust event and at 1.1 km during the second dust event, with a maximum value of 2.74 K day−1 for each case. This significant atmospheric heating induced by elevated dust aerosol layers can affect convection and stability in the lower troposphere.► Dust aerosol properties and radiative effects were assessed in southern China. ► Study help understand the mechanisms of Asian dust transportation. ► The existence of multiple and elevated dust layers. ► Significant shortwave radiative forcings and heating rate during two dust events.
Keywords: Dust; Transport; Vertical structure; Radiative properties; Southeast China;
Carbonate measurements in PM10 near the marble quarries of Carrara (Italy) by infrared spectroscopy (FT-IR) and source apportionment by positive matrix factorization (PMF) by E. Cuccia; A. Piazzalunga; V. Bernardoni; L. Brambilla; P. Fermo; D. Massabò; U. Molteni; P. Prati; G. Valli; R. Vecchi (6481-6487).
The concentration of carbonates in atmospheric Particulate Matter (PM) is usually quite low. The surroundings of marble quarries are peculiar sites where the impact of carbonates in PM levels can be significant. We present here the results of a PM10 sampling campaign performed in Carrara (Italy). The town lies between the famous marble quarries and the harbour: about 1000 trucks per day transport marble blocks and debris from the quarries to the harbour passing through the town centre. PM10 was collected on daily basis on PTFE filters analyzed by Energy-Dispersive X-Ray Fluorescence (ED-XRF) and Ion-Chromatography (IC). Carbonate concentration was measured by a non-destructive Infrared Spectroscopy analysis (FT-IR). Time series of elemental (Na–Pb by ED-XRF), ionic (SO4 2−, NH4 + by ion-chromatography) and carbonate (by FT-IR) concentration values were merged in a unique data set and a PMF analysis singled out the major PM10 sources in the area. Marble transportation turned out to be the major pollution source in the town accounting to PM10 for about 36%; this corresponded to a CaCO3 average level of about 8 μg m−3 during working days. The FT-IR analysis was a crucial part of the work and an ad-hoc analytical procedure was specifically set up, calibrated, and tested as described in the text.
Keywords: Carbonate; PM10; FT-IR; PMF;