Atmospheric Environment (v.109, #C)
Editorial board (i).
Ten years of mercury measurement at urban and industrial air quality monitoring stations in the UK by Richard J.C. Brown; Sharon L. Goddard; David M. Butterfield; Andrew S. Brown; Chris Robins; Chantal L. Mustoe; Elizabeth A. McGhee (1-8).
Concentrations and trends from a decade of measurements of total gaseous mercury and particulate phase mercury at a number of monitoring stations across the UK are presented. Both emissions and ambient concentrations of mercury in the UK have continued to fall slightly during the measurement period despite already being at historically low levels. The median UK concentration of total gaseous mercury recorded in recent years was around 2.0 ng/m3. Small urban increments of about 0.4 ng/m3 above background concentrations were noted, with larger increments above the background only observed close to industrial point sources. The total gaseous mercury to particulate phase mercury ratio was large across the UK – indicating the dominance of the gaseous mercury in the atmosphere – and was observed to be larger at background and urban locations than at industrial sites, as a result of higher relative particulate phase mercury concentrations close to primary emissions point sources.Display Omitted
Keywords: Air quality; Emissions; Particulate matter; Mercury vapour; Long term trends;
Polycyclic aromatic hydrocarbons (PAH) and their genotoxicity in exhaust emissions from a diesel engine during extended low-load operation on diesel and biodiesel fuels by Michal Vojtisek-Lom; Martin Pechout; Luboš Dittrich; Vít Beránek; Martin Kotek; Jaroslav Schwarz; Petr Vodička; Alena Milcová; Andrea Rossnerová; Antonín Ambrož; Jan Topinka (9-18).
This paper investigates the effects of emissions including carcinogenic polycyclic aromatic hydrocarbons (cPAH) of a conventional diesel engine without a particle filter. Experiments were carried on during extended idle and during a loaded operation immediately following the extended idle. Extended low-load operation of diesel engines due to idling and creep at border crossings, loading areas and in severe congestion has been known to deteriorate the combustion and catalytic device performance and to increase the emissions of particulate matter (PM). A conventional diesel engine was coupled to a dynamometer and operated on diesel fuel and neat biodiesel alternately at idle speed and 2% of rated power and at 30% and 100% load at intermediate speed. Exhaust was sampled on fiber filters, from which the content of elemental and organic carbon and polycyclic aromatic hydrocarbons (PAH), including cPAH and benzo[a]pyrene (B[a]P) have been determined. The emissions of cPAH and B[a]P have increased 4–6 times on diesel fuel and by 4–21% on biodiesel during extended idling relative to a short idle and 8–12 times on diesel fuel and 2–20 times on biodiesel during subsequent operation at full load relative to stabilized operation at full load. The total “excess” cPAH emissions after the transition to full load were on the same order of magnitude as the total “excess” cPAH during extended idling. The absolute levels of PAH, cPAH and B[a]P emissions under all operating conditions were lower on biodiesel compared to diesel fuel. Genotoxicity of organic extracts of particles was analysed by acellular assay with calf thymus DNA (CT-DNA) and was consistently higher for diesel than for biodiesel. The exhaust generated during extended idle and subsequent full load exhibited the highest genotoxicity for both fuels. These two regimes are characterized by significant formation of cPAH as well as other DNA reactive compounds substantially contributing to the total genotoxicity. Oxidative DNA damage by all tested extracts was negligible.Display Omitted
Keywords: Biodiesel; Diesel particulate matter; DNA adducts; Emissions; Idling; Creep; DNA oxidative damage; Polycyclic aromatic hydrocarbons; Toxicity of emissions;
Aspect ratio as a function of particle radius: Inversion of extinction and scattering data by Miroslav Kocifaj; František Kundracik (19-22).
The sun and sky photometry made concurrently or, alternatively, simultaneous measurements of extinction and scattering data both represent a valuable tool for gathering the information on aerosol particles. Most typically the size distribution and/or refractive index of aerosol particles can be inferred from multispectral and/or multiangle optical data. Extraction of size-dependent aspect ratio of aerosol particles from optical data is a highly non-trivial task since the kernel of the particular integral equation is a non-linear function of the sought solution. The iterative solution to this problem is introduced and demonstrated on synthetically generated data. It is shown that retrieval of size-dependent aspect ratio is possible even for complex morphologies, most typically for irregularly shaped dust particles.
Keywords: Nonspherical particles; Aspect ratio; Light scattering; Multispectral extinction data;
Long-range transport of air pollutants originating in China: A possible major cause of multi-day high-PM10 episodes during cold season in Seoul, Korea by Hye-Ryun Oh; Chang-Hoi Ho; Jinwon Kim; Deliang Chen; Seungmin Lee; Yong-Sang Choi; Lim-Seok Chang; Chang-Keun Song (23-30).
Massive air pollutants originating in China and their trans-boundary transports are an international concern in East Asia. Despite its importance, details in the trans-boundary transport of air pollutants over East Asia and its impact on regional air quality remain to be clarified. This study presents an evidence which strong support that aerosols emitting in China play a major role in the occurrence of multi-day (≥4 days) severe air pollution episodes in cold seasons (October through March) for 2001–2013 in Seoul, Korea, where the concentration of PM10 (particulates with diameters ≤ 10 μm) exceeds 100 μg m−3. Observations show that these multi-day severe air pollution episodes occur when a strong high-pressure system resides over the eastern China–Korea region. In such weather conditions, air pollutants emitted in eastern China/southwestern Manchuria are trapped within the atmospheric boundary layer, and gradually spread into neighboring countries by weak lower tropospheric westerlies. Understanding of trans-boundary transports of air pollutants will advance the predictability of local air quality, and will encourage the development of international measures to improve air quality.
Keywords: PM10 episode; Long-lasting; Trans-boundary transport; Seoul; China;
Seasonal variation of organochlorine pesticides in the gaseous phase and aerosols over the East China Sea by Tianyi Ji; Tian Lin; Fengwen Wang; Yuanyuan Li; Zhigang Guo (31-41).
Eighty paired gaseous phase and PM2.5 (particulate matter < 2.5 μm in diameter) samples, covering four seasons from October 2011 to August 2012 were collected simultaneously from a remote island in the East China Sea (ECS). The samples were analyzed for organochlorine pesticides (OCPs) to determine their seasonal variation and potential sources over the coastal marine environment. The concentrations of individual OCPs in the PM2.5 samples were higher in winter and lower in summer, and the reverse trend was observed for the measured OCP compounds (except hexachlorocyclohexanes, HCHs) in the gaseous phase. Principal component analysis revealed one trend that contributed 40% to PM2.5-bound OCPs characterized by β-HCH, α-HCH, p,p′-dichlorodiphenyldichloroethane (p,p′-DDD), p,p′-dichlorodiphenyldichloroethylene (p,p′-DDE), and chlordanes; whereas two seasonal trends, represented by dichlorodiphenyltrichloroethanes (DDTs) or chlordanes and HCHs, were responsible for 38% and 23% of the gaseous OCPs, respectively. Continental outflow driven by the East Asian monsoon brought large quantities of particulate OCPs to the ECS, especially in winter. Possible fresh sources or net volatilization from the Yangtze River induced by both higher ambient temperature and higher discharge rates caused the higher gaseous DDT and chlordane levels observed in summer. However, the lower concentrations of gaseous HCHs observed in summer suggested that net volatilization had a relatively limited impact on gaseous HCHs due to the long-term prohibition of their use and their low residual levels in the catchment, whereas the elevated concentrations of gaseous HCHs in winter controlled by gas–particle partitioning, resulted from increased particulate HCHs producing a partial shift to gaseous HCHs over ECS.
Keywords: OCP; Gaseous phase; Aerosols; Seasonal variation; Source; East China Sea;
Heterogeneity of passenger exposure to air pollutants in public transport microenvironments by Fenhuan Yang; Daya Kaul; Ka Chun Wong; Dane Westerdahl; Li Sun; Kin-fai Ho; Linwei Tian; Peter Brimblecombe; Zhi Ning (42-51).
Epidemiologic studies have linked human exposure to pollutants with adverse health effects. Passenger exposure in public transport systems contributes an important fraction of daily burden of air pollutants. While there is extensive literature reporting the concentrations of pollutants in public transport systems in different cities, there are few studies systematically addressing the heterogeneity of passenger exposure in different transit microenvironments, in cabins of different transit vehicles and in areas with different characteristics. The present study investigated PM2.5 (particulate matter with aerodynamic diameters smaller than 2.5 μm), black carbon (BC), ultrafine particles (UFP) and carbon monoxide (CO) pollutant concentrations in various public road transport systems in highly urbanized city of Hong Kong. Using a trolley case housing numerous portable air monitors, we conducted a total of 119 trips during the campaign. Transit microenvironments, classified as 1). busy and secondary roadside bus stops; 2). open and enclosed termini; 3). above- and under-ground Motor Rail Transport (MTR) platforms, were investigated and compared to identify the factors that may affect passenger exposures. The pollutants inside bus and MTR cabins were also investigated together with a comparison of time integrated exposure between the transit modes. Busy roadside and enclosed termini demonstrated the highest average particle concentrations while the lowest was found on the MTR platforms. Traffic-related pollutants BC, UFP and CO showed larger variations than PM2.5 across different microenvironments and areas confirming their heterogeneity in urban environments. In-cabin pollutant concentrations showed distinct patterns with BC and UFP high in diesel bus cabins and CO high in LPG bus cabins, suggesting possible self-pollution issues and/or penetration of on-road pollutants inside cabins during bus transit. The total passenger exposure along selected routes, showed bus trips had the potential for higher integrated passenger exposure compared to MTR trips. The present study may provide useful information to better characterize the distribution of passenger exposure pattern in health assessment studies and the results also highlight the need to formulate exposure reduction based air policies in large cities.
Keywords: Black carbon; CO; Bus cabins; Roadside bus stop; Bus terminal; PM2.5; Subway platform; Ultrafine particles;
Impact of lake breezes on ozone and nitrogen oxides in the Greater Toronto Area by G.R. Wentworth; J.G. Murphy; D.M.L. Sills (52-60).
Meteorological and air quality datasets from summertime (May to September, 2010–2012) were analysed in order to assess the influence of lake-breeze circulations on pollutant levels in the Greater Toronto Area (GTA). While previous estimates of the frequency of summer days experiencing lake breezes range between 25 and 32 % for the GTA, a simple algorithm using surface meteorological observations suggested Lake Ontario breezes occurred on 56% of summer days, whereas a more reliable multiplatform approach yielded a frequency of 74%. Data from five air quality stations across the GTA were used to compare air quality on days during which a lake-breeze circulation formed (“lake breeze days”) versus days when one did not (“non-lake breeze days”). Average daytime O3 maxima were 13.6–14.8 ppb higher on lake breeze days relative to non-lake breeze days. Furthermore, the Ontario Ambient Air Quality Criteria (AAQC) for 1-h average O3 (80 ppb) and 8-h average O3 (65 ppb) were exceeded only on lake breeze days and occurred on a total of 30 and 54 days throughout the study period, respectively. A causal link between lake-breeze circulations and enhanced O3 was identified by examining several days in which only some of the air quality sites were inside the lake-breeze circulation. O3 mixing ratios at sites located within the circulation were at least 30 ppb higher than sites outside the circulation, despite similar temperatures, cloud conditions and synoptic regimes across the region. Rapid O3 increases were concurrent with the arrival of the lake-breeze front, suggesting O3-rich air from over the lake is being advected inland throughout the day. Lake-breeze circulations were found to have less impact on nitrogen oxide (NOx) levels. Morning NOx was greater on lake breeze days, probably due to the stagnant conditions favourable for lake breeze formation. During the late afternoon, only inland sites experience increased NOx on lake breeze days, likely as a result of being downwind from near-shore city centres.
Keywords: Lake breeze; Ozone; Greater Toronto Area; Nitrogen oxides;
Aldehydes in relation to air pollution sources: A case study around the Beijing Olympics by Brent Altemose; Jicheng Gong; Tong Zhu; Min Hu; Liwen Zhang; Hong Cheng; Lin Zhang; Jian Tong; Howard M. Kipen; Pamela Ohman-Strickland; Qingyu Meng; Mark G. Robson; Junfeng Zhang (61-69).
This study was carried out to characterize three aldehydes of health concern (formaldehyde, acetaldehyde, and acrolein) at a central Beijing site in the summer and early fall of 2008 (from June to October). Aldehydes in polluted atmospheres come from both primary and secondary sources, which limits the control strategies for these reactive compounds. Measurements were made before, during, and after the Beijing Olympics to examine whether the dramatic air pollution control measures implemented during the Olympics had an impact on concentrations of the three aldehydes and their underlying primary and secondary sources. Average concentrations of formaldehyde, acetaldehyde and acrolein were 29.3 ± 15.1 μg/m3, 27.1 ± 15.7 μg/m3 and 2.3 ± 1.0 μg/m3, respectively, for the entire period of measurements, all being at the high end of concentration ranges measured in cities around the world in photochemical smog seasons. Formaldehyde and acrolein increased during the pollution control period compared to the pre-Olympic Games, followed the changing pattern of temperature, and were significantly correlated with ozone and with a secondary formation factor identified by principal component analysis (PCA). In contrast, acetaldehyde had a reduction in mean concentration during the Olympic air pollution control period compared to the pre-Olympic period and was significantly correlated with several pollutants emitted from local emission sources (e.g., NO2, CO, and PM2.5). Acetaldehyde was also more strongly associated with primary emission sources including vegetative burning and oil combustion factors identified through the PCA. All three aldehydes were lower during the post-Olympic sampling period compared to the before and during Olympic periods, likely due to seasonal and regional effects. Our findings point to the complexity of source control strategies for secondary pollutants.
Keywords: Aldehydes; Air pollution; Acrolein; Pollutant sources; Principal component analysis; Olympics;
Use of isotopic compositions of nitrate in TSP to identify sources and chemistry in South China Sea by Hong-Wei Xiao; Lu-Hua Xie; Ai-Min Long; Feng Ye; Yue-Peng Pan; Da-Ning Li; Zhen-Hua Long; Lin Chen; Hua-Yun Xiao; Cong-Qiang Liu (70-78).
NO3 − concentration, nitrogen and oxygen isotopic compositions (δ15N and δ18O) of NO3 − were measured in total suspended particulates (TSP) at Yongxing Island in the South China Sea (SCS) between Feb. 2013 and Jan. 2014, as well as on two cruises in the northern South China Sea (NSCS). Measurements aimed to identify NO3 − sources, and possible chemical formation processes of NO3 −. The δ15N and δ18O of NO3 − in TSP at Yongxing Island ranged from −2.5 to +4.9‰, and +48.1 to +99.0‰, with annual weighted averages of +1.5‰ and +83.2‰, respectively. Both δ15N and δ18O had higher values in cool months, indicating that NO x sources and oxidants were different between seasons. In cool months, NO x was mainly from anthropogenic sources, particularly from coal combustion in South China, resulting in high nitrogen deposition that was oxidized by O3 to NO3 −. In warm months, natural emissions were an important source of NO x . TSP samples in the NSCS had higher NO3 − concentrations, higher δ15N and lower δ18O values than samples from Yongxing Island over the same period. This suggests that atmospheric processes caused a decrease in NO3 − concentrations and δ15N but increase in δ18O from coast to remote marine. Assuming to oxygen atoms were derived from O3 during transport in cool months, the mean ratio of NO3 − formed by NO x to total NO3 − was calculated to be 47.9%. This suggests the mean loss ratio of NO x was 89% while the loss ratio of NO3 − was 87% during transport between Chinese coastal areas and Yongxing Island in Nov., 2013.
Keywords: Nitrogen isotope; Oxygen isotope; South China Sea; Nitrate; Atmospheric chemical process; Isotopic fractionation;
Theoretical model for the evaporation loss of PM2.5 during filter sampling by Chun-Nan Liu; Sih-Fan Lin; Chuen-Jinn Tsai; Yueh-Chuen Wu; Chung-Fang Chen (79-86).
The evaporation losses of PM2.5 particles in eight different size ranges corresponding to the 4th–10th stages and after filter of the MOUDI were calculated theoretically and then integrated to obtain the total PM2.5 evaporation loss. Results show that when PM2.5 particles are nearly neutral with pH in the range of 7–8, the evaporated concentrations predicted by the present model agree well with the experimental data with an average absolute difference of 20.2 ± 11.1%. When PM2.5 aerosols are acidic with pH less than 3.5, additional loss of nitrate and chloride can occur due to chemical interactions between collected particles and strong acids which are not considered in the present model. Under pH neutral conditions, the theoretical model was then used to examine the effect of PM2.5 concentration, gas-to-particle ratio, ambient temperature and relative humidity on the extent of evaporation loss. Results show that evaporated PM2.5 concentration increases with increasing temperature and decreasing relative humidity, PM2.5 concentration and gas-to-particle ratio.Display Omitted
Keywords: PM2.5; Evaporation loss; Filter-based sampler; Theory for predicting PM2.5 loss;
Identification and monitoring of Saharan dust: An inventory representative for south Germany since 1997 by H. Flentje; B. Briel; C. Beck; M. Collaud Coen; M. Fricke; J. Cyrys; J. Gu; M. Pitz; W. Thomas (87-96).
An inventory of Sahara dust (SD) events at the Hohenpeiβenberg Global Atmosphere Watch station (Germany) is presented for the period 1997–2013. Based on daily in-situ measurements, high Ca2+-ion concentrations and large particle volume concentrations at diameters d p ≈ 0.5–7 μm are inferred as indicators for days influenced by SD. The resulting SD catalogue agrees with SD time series from Schneefernerhaus, Augsburg and Jungfraujoch stations. On average, SD occurs in 5–15 SD events (SDE) per year covering about 10–60 days/yr in the mixing layer. SDE exhibit a clear seasonality with spring and early autumn maxima, and typically last for 1–3 days. SDE are equally frequent but more significant at Alpine levels due to lower background. Wet deposition of Ca2+ at the surface is little correlated (R2 = 0.14) with particle Ca2+ on a daily basis and yields an average annual Ca2+ immission of 0.22 ± 0.04 g/m2 yr, about 40% of which is due to SD. The majority of outstanding weekly Fe and Al depositions are associated with SDE. SD contributes about 0.5 ± 0.1 μg/m3 to the total particle mass with a decreasing trend from 6% to 4% (−0.1%/yr) in the 1997–2013 period. Except from one, all threshold exceedances according to European legislation (daily PM10 > 50 μg/m3) at Hohenpeiβenberg are due to SD. Implications are discussed with respect to SD-related circulation patterns, SD-induced temperature anomalies in weather forecast models and the capability of aerosol models to capture SDE.
Keywords: Saharan dust; PM10; Trend; Climatology;
Co-variability of smoke and fire in the Amazon basin by Amit Kumar Mishra; Yoav Lehahn; Yinon Rudich; Ilan Koren (97-104).
The Amazon basin is a hot spot of anthropogenically-driven biomass burning, accounting for approximately 15% of total global fire emissions. It is essential to accurately measure these fires for robust regional and global modeling of key environmental processes. Here we have explored the link between spatio-temporal variability patterns in the Amazon basin's fires and the resulting smoke loading using 11 years (2002–2012) of data from the Moderate Resolution Imaging Spectroradiometer (MODIS) and the Aerosol Robotic Network (AERONET) observations. Focusing on the peak burning season (July–October), our analysis shows strong inter-annual correlation between aerosol optical depth (AOD) and two MODIS fire products: fire radiative power (FRP) and fire pixel counts (FC). Among these two fire products, the FC better indicates the amount of smoke in the basin, as represented in remotely sensed AOD data. This fire product is significantly correlated both with regional AOD retrievals from MODIS and with point AOD measurements from the AERONET stations, pointing to spatial homogenization of the smoke over the basin on a seasonal time scale. However, MODIS AODs are found better than AERONET AODs observation for linking between smoke and fire. Furthermore, MODIS AOD measurements are strongly correlated with number of fires ∼10–20 to the east, most likely due to westward advection of smoke by the wind. These results can be rationalized by the regional topography and the wind regimes. Our analysis can improve data assimilation of satellite and ground-based observations into regional and global model studies, thus improving the assessment of the environmental and climatic impacts of frequency and distribution variability of the Amazon basin's fires. We also provide the optimal spatial and temporal scales for ground-based observations, which could be used for such applications.
Keywords: Smoke; Fire; AOD; MODIS; AERONET;
Characterization of airborne ice-nucleation-active bacteria and bacterial fragments by Tina Šantl-Temkiv; Maher Sahyoun; Kai Finster; Susan Hartmann; Stefanie Augustin-Bauditz; Frank Stratmann; Heike Wex; Tina Clauss; Niels Woetmann Nielsen; Jens Havskov Sørensen; Ulrik Smith Korsholm; Lukas Y. Wick; Ulrich Gosewinkel Karlson (105-117).
Some bacteria have the unique capacity of synthesising ice-nucleation-active (INA) proteins and exposing them at their outer membrane surface. As INA bacteria enter the atmosphere, they may impact the formation of clouds and precipitation. We studied members of airborne bacterial communities for their capacity to catalyse ice formation and we report on the excretion of INA proteins by airborne Pseudomonas sp. We also observed for the first time that INA biological fragments <220 nm were present in precipitation samples (199 and 482 INA fragments per L of precipitation), which confirms the presence of submicron INA biological fragments in the atmosphere. During 14 precipitation events, strains affiliated with the genus Pseudomonas, which are known to carry ina genes, were dominant. A screening for INA properties revealed that ∼12% of the cultivable bacteria caused ice formation at ≤−7 °C. They had likely been emitted to the atmosphere from terrestrial surfaces, e.g. by convective transport. We tested the ability of isolated INA strains to produce outer membrane vesicles and found that two isolates could do so. However, only very few INA vesicles were released per INA cell. Thus, the source of the submicron INA proteinaceous particles that we detected in the atmosphere remains to be elucidated.
Keywords: INA bacteria; Ice nucleation; Airborne bacteria; Aeromicrobiology; Bioprecipitation; Outer membrane vesicles;
Inhibition of the WNT/β-catenin pathway by fine particulate matter in haze: Roles of metals and polycyclic aromatic hydrocarbons by Kang-Yun Lee; Jun-Ji Cao; Chii-Hong Lee; Ta-Chih Hsiao; Chi-Tai Yeh; Thanh-Tuan Huynh; Yong-Ming Han; Xiang-Dong Li; Kai-Jen Chuang; Linwei Tian; Kin-Fai Ho; Hsiao-Chi Chuang (118-129).
Air pollution might have a great impact on pulmonary health, but biological evidence in response to particulate matter less than 2.5 μm in size (PM2.5) has been lacking. Physicochemical characterization of haze PM2.5 collected from Beijing, Xian and Hong Kong was performed. Biological pathways were identified by proteomic profiling in mouse lungs, suggesting that WNT/β-catenin is important in the response to haze PM2.5. Suppression of β-catenin levels, activation of caspase-3 and alveolar destruction, as well as IL-6, TNF-α and IFN-γ production, were observed in the lungs. The inhibition of β-catenin, TCF4 and cyclin D1 was observed in vitro in response to haze PM2.5. The inhibition of WNT/β-catenin signaling, apoptosis-related results (caspase-3 and alveolar destruction), and inflammation, particularly including caspase-3 and alveolar destruction, were more highly associated with polycyclic aromatic hydrocarbons in haze PM2.5. In conclusion, decreased WNT/β-catenin expression modulated by haze PM2.5 could be involved in alveolar destruction and inflammation during haze episodes.
Keywords: Air pollution; Apoptosis; β-catenin; Metal; Particulate matter; Polycyclic aromatic hydrocarbons;
Biases in greenhouse gases static chambers measurements in stabilization ponds: Comparison of flux estimation using linear and non-linear models by Juan P. Silva; Ana Lasso; Henk J. Lubberding; Miguel R. Peña; Hubert J. Gijzen (130-138).
The closed static chamber technique is widely used to quantify greenhouse gases (GHG) i.e. CH4, CO2 and N2O from aquatic and wastewater treatment systems. However, chamber-measured fluxes over air–water interfaces appear to be subject to considerable uncertainty, depending on the chamber design, lack of air mixing in the chamber, concentration gradient changes during the deployment, and irregular eruptions of gas accumulated in the sediment. In this study, the closed static chamber technique was tested in an anaerobic pond operating under tropical conditions. The closed static chambers were found to be reliable to measure GHG, but an intrinsic limitation of using closed static chambers is that not all the data for gas concentrations measured within a chamber headspace can be used to estimate the flux due to gradient concentration curves with non-plausible and physical explanations. Based on the total data set, the percentage of curves accepted was 93.6, 87.2, and 73% for CH4, CO2 and N2O, respectively. The statistical analyses demonstrated that only considering linear regression was inappropriate (i.e. approximately 40% of the data for CH4, CO2 and N2O were best fitted to a non-linear regression) for the determination of GHG flux from stabilization ponds by the closed static chamber technique. In this work, it is clear that when R2 adj-non-lin > R2 adj-lin, the application of linear regression models is not recommended, as it leads to an underestimation of GHG fluxes by 10–50%. This suggests that adopting only or mostly linear regression models will affect the GHG inventories obtained by using closed static chambers. According to our results, the misuse of the usual R2 parameter and only the linear regression model to estimate the fluxes will lead to reporting erroneous information on the real contribution of GHG emissions from wastewater. Therefore, the R2 adj and non-linear regression model analysis should be used to reduce the biases in flux estimation by the inappropriate application of only linear regression models.
Keywords: Greenhouse gas emission; Closed static chambers; Stabilization ponds; Anaerobic ponds;
Assessment and determinants of airborne bacterial and fungal concentrations in different indoor environments: Homes, child day-care centres, primary schools and elderly care centres by Joana Madureira; Inês Paciência; João Cavaleiro Rufo; Cristiana Pereira; João Paulo Teixeira; Eduardo de Oliveira Fernandes (139-146).
Until now the influence of risk factors resulting from exposure to biological agents in indoor air has been far less studied than outdoor pollution; therefore the uncertainty of health risks, and how to effectively prevent these, remains.This study aimed (i) to quantify airborne cultivable bacterial and fungal concentrations in four different types of indoor environment as well as to identify the recovered fungi; (ii) to assess the impact of outdoor bacterial and fungal concentrations on indoor air; (iii) to investigate the influence of carbon dioxide (CO2), temperature and relative humidity on bacterial and fungal concentrations; and (iv) to estimate bacterial and fungal dose rate for children (3–5 years old and 8–10 years old) in comparison with the elderly.Air samples were collected in 68 homes, 9 child day-care centres, 20 primary schools and 22 elderly care centres, in a total of 264 rooms with a microbiological air sampler and using tryptic soy agar and malt extract agar culture media for bacteria and fungi growth, respectively. For each building, one outdoor representative location were identified and simultaneously studied.The results showed that child day-care centres were the indoor microenvironment with the highest median bacterial and fungal concentrations (3870 CFU/m3 and 415 CFU/m3, respectively), whereas the lowest median concentrations were observed in elderly care centres (222 CFU/m3 and 180 CFU/m3, respectively). Indoor bacterial concentrations were significantly higher than outdoor concentrations (p < 0.05); whereas the indoor/outdoor ratios for the obtained fungal concentrations were approximately around the unit. Indoor CO2 levels were associated with the bacterial concentration, probably due to occupancy and insufficient ventilation. Penicillium and Cladosporium were the most frequently occurring fungi. Children's had two times higher dose rate to biological pollutants when compared to adult individuals. Thus, due to children's susceptibility, special attention should be given to educational settings in order to guarantee their healthy future development.
Keywords: Indoor air; Bacteria; Fungal genera; Children; Elderly; Dose rate;
Modeling inorganic nitrogen deposition in Guangdong province, China by Zhijiong Huang; Shuisheng Wang; Junyu Zheng; Zibing Yuan; Siqi Ye; Daiwen Kang (147-160).
Atmospheric nitrogen deposition is an essential component of acid deposition and serves as one of main sources of nitrogen of the ecosystem. Along with rapidly developed economy, it is expected that the nitrogen deposition in Guangdong province is considerably large, due to substantial anthropogenic reactive nitrogen lost to the Pearl River Delta (PRD) region, one of the most developed region in China. However, characterization of chemical compositions of inorganic nitrogen (IN) deposition and quantification of nitrogen deposition fluxes in time and space in Guangdong province were seldom conducted, especially using a numerical modeling approach. In this study, we established a WRF/SMOKE-PRD/CMAQ model system and expanded 2006-based PRD regional emission inventories to Guangdong provincial ones, including SO2, NOx, VOC, PM10, PM2.5, and NH3 emissions for modeling nitrogen deposition in Guangdong province. Observations, including meteorological observed data, rainfall data, ground-level criteria pollutant measurements, satellite-derived data, and nitrogen deposition fluxes from field measurements were employed in the evaluation of model performance. Results showed that annual nitrogen deposition fluxes in the PRD region and Guangdong province were 31.01 kg N hm−1 a−1 and 26.03 kg N hm−1 a−1, dominated by NHx (including NH3 and NH 4 + ), with a percentage of 63% and 71% of the total deposition flux of IN, respectively. The ratio of dry deposition to wet deposition was approximately 2:1 in the PRD region and about 3:2 in the whole Guangdong province. IN deposition was mainly distributed in the PRD region, Chaozhou, and Maoming, which was similar to the spatial distributions of NOx and NH3 emissions. The spatial distributions of chemical compositions of IN deposition implied that NH3–N and NOx-N tended to deposit in places close to emission sources, while spatial distributions of aerosol NH 4 + − N and NO 3 − − N usually exhibited broader deposition areas, along with long-range transport of fine particles. Distinct temporal trends were found in IN components, especially for wet depositions, with peak values in August.
Keywords: Emission inventory; Nitrogen deposition modeling; CMAQ; Guangdong province;
A study of aerosol optical depth variations over the Indian region using thirteen years (2001–2013) of MODIS and MISR Level 3 data by Manu Mehta (161-170).
Aerosols affect the earth's climate system both on a regional as well as on a global scale. Several studies have identified India (the second most populous country) as one of the regional hot spots of aerosols due its increasing anthropogenic activities. The paper presents a temporal (annual and seasonal) study of aerosol optical depth (AOD) in the country using satellite data for thirteen year period (2001–2013). The Indian region is divided into four sub regions i.e., north, west, east and south. The analysis is carried out using Level 3 data from two satellite sensors, namely, MODIS (1° × 1°) and MISR (0.5° × 0.5°), onboard NASA's Terra platform. Annual and seasonal mean AOD variation has been studied. It is found that annual aerosol loading remains highest in Indo-Gangetic Plains (IGP) in all the years. In winter season, the overall loading is lowest for the entire country while it reaches maximum in the monsoon season. This could be attributed to the relative humidity, wind and associated rainfall patterns in the country. Also, the aerosol tendencies have been computed using the first and last six year period change in aerosol optical depth. Further, annual and seasonal trends in AOD have been calculated using weighted least square regression approach and the results have been compared. Statistically significant trends are reported at 95% confidence level. Weights are assigned corresponding to the expected errors associated with the satellite data. There is a good agreement in the seasonal tendencies and trends computed from both the sensors for winter, monsoon and post-monsoon seasons. Significantly increasing trends are found in winter and post-monsoon seasons which could be due to increase in anthropogenic activities. All the observations are separately reported for ten most populous cities of India. Delhi and Kolkata are amongst the most polluted cities in India.
Keywords: Aerosol optical depth; MODIS; MISR; India; Trends; Tendencies;
On the source inversion of fugitive surface layer releases. Part I. Model formulation and application to simple sources by V. Sanfélix; A. Escrig; A. López-Lilao; I. Celades; E. Monfort (171-177).
Source inversion by dispersion modelling of fugitive particulate matter (PM) emissions entails considerable difficulty. Fugitive PM sources are rarely steady or point sources. They occur near the ground, where there are high vertical gradients of wind velocity and potential temperature. To resolve the source from the background concentrations, measurements need to be conducted very close to the source. In this study, a dispersion model was developed that consists of numerically solving the pollutant transport equation, while incorporating the Monin–Obukhov similarity theory. By using this numerical approach, in contrast to Gaussian dispersion models, wind shear effects and plume meandering were accounted for directly. A series of controlled experiments were conducted, in which the fugitive PM sources were parameterized as much as possible. The developed model was used to obtain operation-specific PM10 emission factors (EFs). This is the first of two articles describing the model and the field campaigns in which it was applied to determine the EFs. Part I describes the mathematical model and its application to two relatively simple sources.
Keywords: Dispersion modelling; Emission factor; Fugitive emissions; Particulate matter; Atmospheric surface layer;
Characterization of ambient PM2.5 at a pollution hotspot in New Delhi, India and inference of sources by Pallavi Pant; Anuradha Shukla; Steven D. Kohl; Judith C. Chow; John G. Watson; Roy M. Harrison (178-189).
Ambient PM2.5 samples were collected at a high-traffic location (summer and winter 2013) and characterized for a large suite of elemental and organic markers. Concentrations were found to exceed the Indian PM2.5 air quality standard on several occasions, especially in the winter. Winter concentrations of several individual tracer species were several fold higher compared to summer, particularly for some PAHs and trace metals. Enrichment factors relative to crustal material showed significant enrichment for elements such as Ti, Sb, Pb and As, although Ba, often used as a marker for non-exhaust emissions from traffic was not found to be enriched appreciably. Crustal material was found to be an important contributor in the summer (14.3%), while wood burning (23.3%), nitrates (12.4%) and chlorides (12.3%) were found to be major contributors in winter. The contribution of road traffic exhaust emissions was estimated to be 18.7% in summer and 16.2% in winter. Other combustion sources (wood and other biomass/waste/coal) were found to be a significant source in winter, and contribute to the higher concentrations. Secondary sulphates, nitrates and chloride (the latter two in winter) and organic matter also contribute substantially to PM2.5 mass.
Keywords: Molecular markers; Traffic; India; Mass closure; Particulate matter;
Measurements of emission factors of PM2.5, OC, EC, and BC for household stoves of coal combustion in China by Yingjun Chen; Chongguo Tian; Yanli Feng; Guorui Zhi; Jun Li; Gan Zhang (190-196).
As follow-up efforts for measurements on emission factors (EFs) of fine particulate matter (PM2.5) and its carbonaceous fractions for China's household coal stoves, a large-sized dilution sampling system was designed to test a total of 20 coal/stove combinations, which involve five coals with wide-ranged geological maturities and three stoves. Coal smoke was simultaneously collected onto quartz filter for organic carbon (OC) and elemental carbon (EC) analyses by thermal-optical reflectance (TOR) protocol and monitored online for optical black carbon (BC) by Aethalometer. The mean EFs based on burned fuel weight of PM2.5, OC, EC, and BC are 4.25 ± 2.45, 1.11 ± 0.72, 1.43 ± 1.17, and 0.60 ± 0.42 g/kg for bituminous coal, and 1.44 ± 0.67, 0.05 ± 0.02, 0.04 ± 0.02, and 0.01 ± 0.01 g/kg for anthracite, respectively. Significant differences are observed among the EFs for various coal/stove combinations, which are attributable to the differences of coal maturity, burning style and stove efficiency. Although the EFs of BC and EC are closely correlated (r = 0.97), the average BC/EC ratio is only 0.39, indicating a significant gap between the two methods; and the optical attenuation cross-section (σ) for fresh coal smoke can be deduced as 6.47 m2/g, much lower than the manufacturer's preset value of 16.6 m2/g for Aethalometer.
Keywords: Emission factor; Experimental measurement; Fine particle; Black carbon; Elemental carbon; Residential coal combustion;
Effects of a high-fibre diet on ammonia and greenhouse gas emissions from gestating sows and fattening pigs by François-Xavier Philippe; Martine Laitat; José Wavreille; Baudouin Nicks; Jean-François Cabaraux (197-204).
This study aims to measure under barn conditions the emissions of NH3, N2O, CH4 and CO2 associated with gestating sows (trial 1) and fattening pigs (trial 2) fed either a control diet (CTD) based on cereals or a high-fibre diet (HFD) based on sugar beet pulp (SBP). Three successive batches of 10 Belgian Landrace gestating sows were used for trial 1. Two successive batches of 24 Piétrain × Belgian Landrace fattening pigs were used for trial 2. Animals were kept on slatted floor. The gas emissions were measured by infrared photoacoustic detection and expressed per day and per livestock unit, equals to 500 kg body weight. Similar trends were observed for both animal types. With HFD, the NH3 emissions were reduced (27.2 vs. 36.5 g for the gestating sows, P < 0.001; 23.2 vs. 45.0 g for the fattening pigs, P < 0.001) but the CH4 emissions were increased (41.5 vs. 21.0 g for gestating sows, P < 0.001; 37.9 vs. 27.2 g for fattening pigs, P < 0.001). The fibre content of the diet had not significant impact on N2O emissions (around 1.4 g for gestating sows and 2.1 g for fattening pigs, P > 0.05), and on CO2 emissions (around 6.0 kg for gestating sows and 9.1 kg for fattening pigs, P > 0.05). Most of manure parameters did not statistically differ regarding the treatment. Reproductive performance and body condition of the sows were not affected by the diet. However, growth performance and carcass traits of the HFD-fed fattening pigs were deteriorated compared to CTD.
Keywords: Ammonia; Carbon dioxide; Methane; Nitrous oxide; Sugar beet pulp; Swine production;
Multicriteria approach to interpret the variability of the levels of particulate matter and gaseous pollutants in the Madrid metropolitan area, during the 1999–2012 period by P. Salvador; B. Artíñano; M.M. Viana; A. Alastuey; X. Querol (205-216).
The evolution of the mean levels of particulate matter (PM) and gaseous pollutants recorded in the Madrid metropolitan area from 1999 to 2012, were investigated focussing on the impact of mitigation strategies and economic scenarios. Temporal trends have shown that SO2, CO, NO, PM10 and NO2 levels at Madrid kerbside and urban-background sites have been decreasing over the 1999-2012 period, with statistical significance. A small contribution to the annual decreasing rates of SO2, NO and NO2 obtained at these sites could be attributed to the reduction in the regional background levels. The reduction in the emissions of atmospheric pollutants from specific sources of the urban agglomeration, explained most of the annual decreasing rates obtained at the kerbside and urban-background sites. From 1999 to 2007 a reduction of the emissions from road traffic and residential heating was produced, as a consequence of the implementation of a number of management strategies promoted and adopted by European and national public administrations. In contrast, from 2008 to 2012 a deep decrease in fuel consumption and a reduction of construction-demolition and roadwork activities took place in the Madrid metropolitan area, as a consequence of the economic recession. The expected overcoming of the economic crisis within the next few years, will presumably give rise to similar levels of PM and gaseous pollutants as those existing previously to the crisis period. The introduction of new Euro 6/VI vehicles which emit considerably less NOx than previous generation diesel vehicles, as well as the implementation of strategies aimed at reducing resuspended mineral dust from road traffic and construction-demolition activities are thus encouraged.
Keywords: Urban air pollution; Trend analysis; PM10; PM2.5; Gaseous pollutants; Air quality policy;
Time-resolved inorganic chemical composition of fine aerosol and associated precursor gases over an urban environment in western India: Gas-aerosol equilibrium characteristics by A.K. Sudheer; R. Rengarajan (217-227).
Inorganic ionic constituents (Na+, NH4 +, K+, Mg2+, Ca2+, Cl−, NO3 − and SO4 2−) of PM2.5 and associated trace gases (NH3, HNO3 and HCl) were measured simultaneously by Ambient Ion Monitor – Ion Chromatograph (AIM-IC) system with a time resolution of one hour at an urban location in semi-arid region of western India during summer and winter. The average NH3, HNO3 and HCl concentrations were 11.6 ± 5.0, 2.9 ± 0.8 and 0.15 μg m−3, respectively, during winter. During summer, NH3 and HNO3 concentrations were of similar magnitude, whereas HCl concentration was less than ∼0.03 μg m−3. NH3 concentration exhibited a distinct diurnal variation during both seasons. However, HNO3 did not show a specific diurnal trend during the observation period in both seasons. The data obtained were used to study gas-aerosol equilibrium characteristics using a thermodynamic equilibrium model, ISORROPIA II. The results suggest that NH3 exists in equilibrium between measured fine-mode particle and gas phase with a systematic bias of ∼14%, whereas HCl and HNO3 deviate significantly from the modelled data. These observations have implications on thermodynamic equilibrium assumptions used for estimating various aerosol parameters such as liquid water content, pH, etc., thus causing significant bias in chemical transport model results over the study region.
Keywords: Aerosol composition; Thermodynamic equilibrium; Trace gases;
Past, present, and future emissions of HCFC-141b in China by Ziyuan Wang; Huanghuang Yan; Xuekun Fang; Lingyun Gao; Zihan Zhai; Jianxin Hu; Boya Zhang; Jianbo Zhang (228-233).
According to the Montreal Protocol, China is required to phase-out hydrochlorofluorocarbons (HCFCs) by 2030. Compound 1,1-dichloro-1-fluoroethane (CH3CCl2F, HCFC-141b) has an ozone depleting potential (ODP, 0.11) and global warming potential (GWP, 782), and is widely used in the polyurethane foam and solvent sectors in China. This study compiles a comprehensive emission inventory of HCFC-141b during 2000–2013 and makes a projection to 2050. Our results showed that HCFC-141b emissions in China increased from 0.8 Gg/yr (0.6 CO2-eq Tg/yr) in 2000 to 15.8 Gg/yr (12.4 CO2-eq Tg/yr) in 2013 with an accelerated growth rate. The provincial emission distribution showed that Shandong, Jiangsu, and Guangdong are key emission areas in China. A large amount of stock was retained in installed equipment, which may have an impact in the future. For future phasing-out, it was estimated that under the Montreal Planned Phase-out scenario (MPP), the accumulative reduction of HCFC-141b emissions during 2014–2050 would be 3071.0 Gg (2401.5 CO2-eq Tg) compared to that under the Business-as-usual (BAU) scenario. This study reviewed and predicted HCFC-141b emissions and their environmental impacts in China.
Keywords: HCFC-141b; National emission inventory; Provincial distribution; Phase-out scenario;
Spring and summer night-time high ozone episodes in the upper Brahmaputra valley of North East India and their association with lightning by Chandrakala Bharali; Binita Pathak; Pradip Kumar Bhuyan (234-250).
Simultaneous and round the clock measurement during thunderstorm and lightning has been used to study the impact of lightning generated NOx (LNOx) on O3 mixing ratio within the boundary layer during night-time. Lightning flash rate obtained from Lightning Image Sensor (LIS) on board TRMM over the Brahmaputra valley centred around Dibrugarh has been used to identify the events in which NOx was elevated with simultaneous dip in O3 for a short duration followed by subsequent elevation of O3 in spring and summer of 2012–2014. Seasonally averaged O3 attains higher values at night on thunderstorm days as compared to that on clear and cloudy days both in spring and summer i.e. as against a minimum night-time (1700–0500 h) values of ∼3 ppb on clear days, the mean night-time level on thunderstorm days is ∼18 ppb in spring and ∼12 ppb in summer. The estimated steady state O3 concentration is well correlated with the NO2/NO ratio and found to be ∼33% of the measured O3. One day isentropic concentration weighted trajectory (CWT) analysis carried out for the spring and summer seasons reveal that part of GWB and Bangladesh are the potential additional source of O3 in both the seasons. LNOx is found to contribute to ∼33% of the measured O3 during the study period. Enhancement of O3 is well correlated with the lightning radiance indicating direct photodissociation of O3 due to lightning. ΔO3 is independent of the location of the flash rather depends on flash intensity.
Keywords: LNOx; LO3; Lightning; CWT; Trace gas; LIS;
Atmospheric particulate mercury in the megacity Beijing: Spatio-temporal variations and source apportionment by N.J. Schleicher; J. Schäfer; G. Blanc; Y. Chen; F. Chai; K. Cen; S. Norra (251-261).
Particulate mercury (HgP) concentrations in weekly aerosol samples (PM2.5 and TSP) from Beijing, China, were measured for a complete year. In addition, spatial differences were measured for a shorter time period at four different sites and potential source materials were analyzed. Average HgP concentrations in PM2.5 samples were 0.26 ng/m3 for day-time PM2.5, 0.28 ng/m3 for night-time PM2.5, and 0.57 ng/m3 for TSP samples, respectively. Coal combustion was identified as the major source of HgP in Beijing. Other sources included industrial activities as well as red color on historical buildings as a minor contribution. Spatial differences were pronounced with highest concentrations in the inner city (inside the 3rd ring road). The results further showed a strong seasonality with highest concentrations in winter and lowest in summer due to local meteorological conditions (precipitation in summer and stagnant conditions and low mixing layer height in winter) as well as seasonal sources, such as coal combustion for heating purposes. Day–night differences also showed a seasonal pattern with higher night-time concentrations during summer and higher day-time concentrations during winter. Compared to other cities worldwide, the HgP concentrations in Beijing were alarmingly high, suggesting that airborne particulate Hg should be the focus of future monitoring activities and mitigation measures.
Keywords: Mercury (Hg); Particle-bound mercury (HgP); Urban aerosols; Air pollution;
The near-source impacts of diesel backup generators in urban environments by Zheming Tong; K. Max Zhang (262-271).
Distributed power generation, located close to consumers, plays an important role in the current and future power systems. However, its near-source impacts in complex urban environments are not well understood. In this paper, we focused on diesel backup generators that participate in demand response (DR) programs. We first improved the micro-environmental air quality simulations by employing a meteorology processor, AERMET, to generate site-specific boundary layer parameters for the Large Eddy Simulation (LES) modeling. The modeling structure was then incorporated into the CTAG model to evaluate the environmental impacts of diesel backup generators in near-source microenvironments. We found that the presence of either tall upwind or downwind building can deteriorate the air quality in the near-stack street canyons, largely due to the recirculation zones generated by the tall buildings, reducing the near-stack dispersion. Decreasing exhaust momentum ratio (stack exit velocity/ambient wind velocity) draws more exhaust into the recirculation zone, and reduces the effective stack height, which results in elevated near-ground concentrations inside downwind street canyons. The near-ground PM2.5 concentration for the worst scenarios could well exceed 100 μg m−3, posing potential health risk to people living and working nearby. In general, older diesel backup generators (i.e., Tier 1, 2 or older) without the up-to-date emission control may significantly increase the pollutant concentration in the near-source street canyons if participating in DR programs. Even generators that comply with Tier-4 standards could lead to PM hotspots if their stacks are next to tall buildings. Our study implies that the siting of diesel backup generators stacks should consider not only the interactions of fresh air intake and exhaust outlet for the building housing the backup generators, but also the dispersion of exhaust plumes in the surrounding environment.
Keywords: Distributed generation; Emergency generator; Plume dispersion; Micrometeorology; Atmospheric stability; CFD;
Kinetics of the gas-phase reaction between ozone and three unsaturated oxygenated compounds: Ethyl 3,3-dimethyl acrylate, 2-methyl-2-pentenal and 6-methyl-5-hepten-2-one at atmospheric pressure by Elizabeth Gaona Colmán; María B. Blanco; Ian Barnes; Mariano A. Teruel (272-278).
Rate coefficients for the gas-phase reactions of O3 molecules with three unsaturated oxygenated compounds have been determined using the relative kinetic technique in an environmental chamber with FTIR detection of the reactants at (298 ± 2) K in 760 Torr total pressure of synthetic air. The following rate coefficients (in units of 10−17 cm3 molecule−1 s−1) were determined: ethyl 3,3-dimethyl acrylate (0.82 ± 0.19), 2-methyl-2-pentenal (0.71 ± 0.16) and 6-methyl-5-hepten-2-one (26 ± 7).The different reactivity of the unsaturated oxygenated compounds toward O3 is discussed in terms of their chemical structure. In addition, a correlation between the reactivity of structurally different unsaturated compounds (alkenes and unsaturated oxygenated VOCs, such as ethers, esters, aldehydes, ketones and alcohols) toward O3 molecules and the HOMO (Highest Occupied Molecular Orbital) of the compounds is presented.Using the kinetic parameters determined in this work, residence times of these unsaturated compounds in the atmosphere with respect to reaction with O3 have been calculated. In urban and rural areas the main sink of 6-methyl-5-hepten-2-one is reaction with O3 molecules with a residence time in the order of few minutes.Display Omitted
Keywords: Unsaturated oxygenated compounds; Ozonolysis; Relative kinetic method; Rate coefficients; Tropospheric chemistry;
Introduction to the special issue on observations and source attribution of ozone in rural regions of the western United States by Allen S. Lefohn; Owen R. Cooper (279-281).
Comparison of background ozone estimates over the western United States based on two separate model methodologies by Pat Dolwick; Farhan Akhtar; Kirk R. Baker; Norm Possiel; Heather Simon; Gail Tonnesen (282-296).
Two separate air quality model methodologies for estimating background ozone levels over the western U.S. are compared in this analysis. The first approach is a direct sensitivity modeling approach that considers the ozone levels that would remain after certain emissions are entirely removed (i.e., zero-out modeling). The second approach is based on an instrumented air quality model which tracks the formation of ozone within the simulation and assigns the source of that ozone to pre-identified categories (i.e., source apportionment modeling). This analysis focuses on a definition of background referred to as U.S. background (USB) which is designed to represent the influence of all sources other than U.S. anthropogenic emissions. Two separate modeling simulations were completed for an April–October 2007 period, both focused on isolating the influence of sources other than domestic manmade emissions. The zero-out modeling was conducted with the Community Multiscale Air Quality (CMAQ) model and the source apportionment modeling was completed with the Comprehensive Air Quality Model with Extensions (CAMx). Our analysis shows that the zero-out and source apportionment techniques provide relatively similar estimates of the magnitude of seasonal mean daily 8-h maximum U.S. background ozone at locations in the western U.S. when base case model ozone biases are considered. The largest differences between the two sets of USB estimates occur in urban areas where interactions with local NOx emissions can be important, especially when ozone levels are relatively low. Both methodologies conclude that seasonal mean daily 8-h maximum U.S. background ozone levels can be as high as 40–45 ppb over rural portions of the western U.S. Background fractions tend to decrease as modeled total ozone concentrations increase, with typical fractions of 75–100 percent on the lowest ozone days (<25 ppb) and typical fractions between 30 and 50% on days with ozone above 75 ppb. The finding that estimates of background ozone are not strongly dependent on the technique applied lends credibility to this and earlier modeling work.
Keywords: Ozone; Background ozone; U.S. background; Zero-out modeling; Source apportionment; CMAQ; CAMx;
Ozone enhancement in western US wildfire plumes at the Mt. Bachelor Observatory: The role of NO x by P. Baylon; D.A. Jaffe; N.L. Wigder; H. Gao; J. Hee (297-304).
We looked at 19 wildfire events that were observed in the summers of 2012 and 2013 at the Mt. Bachelor Observatory (MBO, 2.7 km a.s.l.), a mountaintop site located in central Oregon. We identified wildfire plumes using enhancement ratios (ΔY/ΔX), which we calculated for each plume by taking the Reduced Major Axis linear regression slope of various species. We reported the calculated enhancement ratios and explored their relationship with ozone production. We observed a negative correlation between ΔO3/ΔCO and ΔNO x /ΔNO y (r = −0.72). This showed that the degree of NO x oxidation is a key predictor of ozone production. The highest ΔNO x /ΔNO y (0.57 pptv/pptv) was associated with ozone loss (ozone titration). Low ΔNO x /ΔNO y values (ranging from 0.049 to 0.15 pptv/pptv) are generally associated with ozone enhancement. We also found that even if ΔO3/ΔCO is low, ΔO3 may still be significant if CO enhancements are large. We then explored events that are not associated with any O3 enhancement/loss. Out of 19 fire events, 3 belong to this category. We discovered that these events are either BL-influenced (O3 deposition), associated with low ΔNO y /ΔCO ratios, and/or associated with minimal photochemistry (due to nighttime transport). Absolute ozone enhancements ranged from 3.8 to 32 ppbv, while ozone production efficiencies (OPEs) ranged from 2.1 to 17. However, because PAN comprises most of the reactive nitrogen in fire plumes, the calculated OPEs underestimated the true ozone mixing ratios. OPEs may therefore be misleading indicators of ozone production in wildfires. Finally, we segregated the data into plume/non-plume time periods. From this we found that the average O3 mixing ratio was significantly higher in fire plumes compared to non-plume time periods, and the noontime NO/NO2 ratios were also higher. This later result gives insight into the photochemical environment in the fire plumes.
Keywords: Ozone production; Wildfire; Enhancement ratio; Western U.S;
An overview of the 2013 Las Vegas Ozone Study (LVOS): Impact of stratospheric intrusions and long-range transport on surface air quality by A.O. Langford; C.J. Senff; R.J. Alvarez; J. Brioude; O.R. Cooper; J.S. Holloway; M.Y. Lin; R.D. Marchbanks; R.B. Pierce; S.P. Sandberg; A.M. Weickmann; E.J. Williams (305-322).
The 2013 Las Vegas Ozone Study (LVOS) was conducted in the late spring and early summer of 2013 to assess the seasonal contribution of stratosphere-to-troposphere transport (STT) and long-range transport to surface ozone in Clark County, Nevada and determine if these processes directly contribute to exceedances of the National Ambient Air Quality Standard (NAAQS) in this area. Secondary goals included the characterization of local ozone production, regional transport from the Los Angeles Basin, and impacts from wildfires. The LVOS measurement campaign took place at a former U.S. Air Force radar station ∼45 km northwest of Las Vegas on Angel Peak (∼2.7 km above mean sea level, asl) in the Spring Mountains. The study consisted of two extended periods (May 19–June 4 and June 22–28, 2013) with near daily 5-min averaged lidar measurements of ozone and backscatter profiles from the surface to ∼2.5 km above ground level (∼5.2 km asl), and continuous in situ measurements (May 20–June 28) of O3, CO, (1-min) and meteorological parameters (5-min) at the surface. These activities were guided by forecasts and analyses from the FLEXPART (FLEXible PARTticle) dispersion model and the Real Time Air Quality Modeling System (RAQMS), and the NOAA Geophysical Research Laboratory (NOAA GFDL) AM3 chemistry-climate model. In this paper, we describe the LVOS measurements and present an overview of the results. The combined measurements and model analyses show that STT directly contributed to each of the three O3 exceedances that occurred in Clark County during LVOS, with contributions to 8-h surface concentrations in excess of 30 ppbv on each of these days. The analyses show that long-range transport from Asia made smaller contributions (<10 ppbv) to surface O3 during two of those exceedances. The contribution of regional wildfires to surface O3 during the three LVOS exceedance events was found to be negligible, but wildfires were found to be a major factor during exceedance events that occurred before and after the LVOS campaign. Our analyses also shows that ozone exceedances would have occurred on more than 50% of the days during the six-week LVOS campaign if the 8-h ozone NAAQS had been 65 ppbv instead of 75 ppbv.
Keywords: Background ozone; Stratosphere-to-troposphere transport; Long range transport; Asian pollution; Surface ozone; NAAQS; Exceedances;
Causes of increasing ozone and decreasing carbon monoxide in springtime at the Mt. Bachelor Observatory from 2004 to 2013 by L.E. Gratz; D.A. Jaffe; J.R. Hee (323-330).
We report trends in springtime ozone (O3) and carbon monoxide (CO) at the Mt. Bachelor Observatory (MBO) in central Oregon, U.S.A. from 2004 to 2013. Over the 10-year period the median and 95th percentile springtime O3 increased by 0.76 ± 0.61 ppbv yr−1 (1.7 ± 1.4% yr−1) and 0.87 ± 0.73 ppbv yr−1 (1.5 ± 1.2% yr−1), respectively. These trends are consistent with reported positive trends in springtime O3 in the western U.S. In contrast, median CO decreased by −3.1 ± 2.4 ppbv yr−1 (−1.9 ± 1.4% yr−1), which is highly similar to springtime North Pacific surface flask measurements from 2004 to 2012. While a 10-year record is relatively short to evaluate long-term variability, we incorporate transport model analysis and contextualize our measurements with reported northern mid-latitude trends over similar time frames to investigate the causes of increasing O3 and decreasing CO at MBO. We performed cluster analysis of 10-day HYSPLIT back-trajectories from MBO and examined O3 and CO trends within each cluster. Significant positive O3 trends were associated with high-altitude, rapid transport from East Asia. Significant negative CO trends were most associated with transport from the North Pacific and Siberia, as well as from East Asia. The rise in springtime O3 is likely associated with increasing O3 precursor emissions in Asia and long-range transport to the western U.S. The decline in springtime CO appears linked to decreasing Northern Hemisphere background CO, largely due to anthropogenic emissions reductions in Europe and North America, and also to a recently reported decline in total CO output from China caused by more efficient combustion. These springtime O3 and CO trends suggest that hydroxyl radical (OH) mixing ratios in the North Pacific may have increased over the study period.
Keywords: Ozone; Carbon monoxide; Western U.S.; Long-term trends; Trajectory cluster analysis; Asian long-range transport;
Transport aloft drives peak ozone in the Mojave Desert by Richard VanCuren (331-341).
Transport of anthropogenic pollution eastward out of the Los Angeles megacity region in California has been periodically observed to reach the Colorado River and the Colorado Plateau region beyond. In the 1980s, anthropogenic halocarbon tracers measured in and near the Las Angeles urban area and at a mountain-top site near the Colorado River, 400 km downwind, were shown to have a correlated seven-day cycle explainable by transport from the urban area with a time lag of 1–2 days. Recent short term springtime intensive studies using aircraft observations and regional modeling of long range transport of ozone from the Southern California megacity region showed frequent and persistent ozone impacts at surface sites across the Colorado Plateau and Southern Rocky Mountain region, at distances up to 1500 km, also with time lags of 1–2 days. However, the timing of ozone peaks at low altitude monitoring sites within the Mojave Desert, at distances from 100 to 400 km from the South Coast and San Joaquin Valley ozone source regions, does not show the expected time-lag behavior seen in the larger transport studies. This discrepancy is explained by recognizing ozone transport across the Mojave Desert to occur in a persistent layer of polluted air in the lower free troposphere with a base level at approximately 1 km MSL. This layer impacts elevated downwind sites directly, but only influences low altitude surface ozone maxima through deep afternoon mixing. Pollutants in this elevated layer derive from California source regions (the Los Angeles megacity region and the intensive agricultural region of the San Joaquin Valley), from long-range transport from Asia, and stratospheric down-mixing. Recognition of the role of afternoon mixing during spring and summer over the Mojave explains and expands the significance of previously published reports of ozone and other pollutants observed in and over the Mojave Desert, and resolves an apparent paradox in the timing of ozone peaks due to short-range and long-range transport from the upwind basins.
Keywords: Ozone transport; California; SOCAB; SJVAB; MDAB; Mojave Desert; Las Vegas; Non-attainment;
Characterizing the impacts of vertical transport and photochemical ozone production on an exceedance area by Emma L. Yates; Laura T. Iraci; David Austerberry; R. Bradley Pierce; Matthew C. Roby; Jovan M. Tadić; Max Loewenstein; Warren Gore (342-350).
Offshore and inland vertical profiles of ozone (O3) were measured from an aircraft during 16 flights from January 2012 to January 2013 over the northern San Joaquin Valley (SJV) and over the Pacific Ocean. Analysis of in situ measurements presents an assessment of the seasonality and magnitude of net O3 production and transport within the lower troposphere above the SJV. During the high O3 season (May–October), the Dobson Unit sum of O3 in the 0–2 km above sea level (km.a.s.l.) layer above the SJV exceeds that above the offshore profile by up to 20.5%, implying net O3 production over the SJV or vertical transport from above. During extreme events (e.g. Stratosphere-to-troposphere transport) vertical features (areas of enhanced or depleted O3 or water vapor) are observed in the offshore and SJV profiles at different altitudes, demonstrating the scale of vertical mixing during transport. Correlation analysis between offshore O3 profiles and O3 surface sites in the SJV lends further support the hypothesis of vertical mixing. Correlation analysis indicates that O3 mixing ratios at surface sites in the northern and middle SJV show significant correlations to the 1.5–2 km.a.s.l. offshore altitude range. Southern SJV O3 surface sites show a shift towards maximum correlations at increased time-offsets, and O3 surface sites at elevated altitudes show significant correlations with higher offshore altitudes (2.5–4 km.a.s.l.).
Keywords: Tropospheric ozone; Air quality; San Joaquin Valley;
Surface ozone in the Lake Tahoe Basin by Joel D. Burley; Sandra Theiss; Andrzej Bytnerowicz; Alan Gertler; Susan Schilling; Barbara Zielinska (351-369).
Surface ozone (O3) concentrations were measured in and around the Lake Tahoe Basin using both active monitors (2010) and passive samplers (2002, 2010). The 2010 data from active monitors indicate average summertime diurnal maxima of approximately 50–55 ppb. Some site-to-site variability is observed within the Basin during the well-mixed hours of 10:00 to 17:00 PST, but large differences between different sites are observed in the late evening and pre-dawn hours. The observed trends correlate most strongly with elevation, topography, and surface vegetation. High elevation sites with steeply sloped topography and drier ground cover experience elevated O3 concentrations throughout the night because they maintain good access to downward mixing of O3-rich air from aloft with smaller losses due to dry deposition. Low elevation sites with flat topography and more dense surface vegetation experience low O3 concentrations in the pre-dawn hours because of greatly reduced downward mixing coupled with enhanced O3 removal via efficient dry deposition. Additionally, very high average O3 concentrations were measured with passive samplers in the middle of the Lake in 2010. This latter result likely reflects diminished dry deposition to the surface of the Lake. High elevation Tahoe Basin sites with exposure to nocturnal O3-rich air from aloft experience daily maxima of 8-h average O3 concentrations that are frequently higher than concurrent maxima from the polluted upwind comparison sites of Sacramento, Folsom, and Placerville. Wind rose analyses of archived NAM 12 km meteorological data for the summer of 2010 suggest that some of the sampling sites situated near the shoreline may have experienced on-shore “lake breezes” during daytime hours and/or off-shore “land breezes” during the night. Back-trajectory analysis with the HYSPLIT model suggests that much of the ozone measured at Lake Tahoe results from the transport of “polluted background” air into the Basin from upwind pollution source regions. Calculation of ozone exposure indices indicates that the two most polluted sites sampled by active monitors in 2010 – the highest Genoa Peak site, located on the eastern side of the Lake at an elevation of 2734 m above sea level, and Angora Lookout, located to the south–southwest (SSW) of the Lake at an elevation of 2218 m above sea level – likely experienced some phytotoxic impacts, while the other Tahoe Basin locations received lower ozone exposures.
Keywords: Lake Tahoe; Portable ozone monitor; Passive samplers; Spatial interpolation; Ozone exposure indices; HYSPLIT;