Atmospheric Environment (v.45, #7)

A review of major chlorofluorocarbons and their halocarbon alternatives in the air by Ki-Hyun Kim; Zang-Ho Shon; Hang Thi Nguyen; Eui-Chan Jeon (1369-1382).
To establish a proper regulation strategy on the emissions of major halocarbons including chlorofluorocarbons (CFCs), carbon tetrachloride (CCl4), hydrochlorofluorocarbons (HCFCs) and hydrofluorocarbons (HFCs), it is essential to assess their environmental behavior in relation to social and technological changes for their control. The production and release of CFCs and CCl4 increased rapidly to peak between the 1970s and 1980s and then decreased dramatically from the end of the 1980s in good accordance with the phase out schedules set by the Montreal Protocol. Both HCFCs (e.g., HCFC-124, HCFC-141b, and HCFC-142b) and HFCs (e.g., HFC-134a) have been introduced as CFCs alternatives between the late 1980s and early 1990s. However, these alternatives have already been or will be scheduled to be phased out because of their involvement in ozone destruction and global warming. In light of all the complexities associated with the global chemistry of CFCs and their alternatives, this paper provides an overview of their production and emission trends, their relationship with the ozone depletion phenomenon, the chemistry regulating their removal processes, and their distribution patterns with diverse temporal and spatial scales.► To regulate the emissions of halocarbons, their environmental behavior needs to be assessed. ► We discuss an overview of their production and emission trends along with the ozone depletion. ► We also cover the chemistry regulating their removal processes and their distribution patterns. ► We also attempted to elucidate the basic factors underlying interim replacement compounds. ► The problems associated with these alternatives are evaluated for their roles in global chemistry.
Keywords: Chlorofluorocarbons (CFCs); Carbon tetrachloride (CCl4); Hydrochlorofluorocarbons (HCFCs); Hydrofluorocarbons (HFCs); Montreal protocol;

We have developed a framework for a three-dimensional regional air quality simulation that is applicable to various air quality studies over Japan. The framework consists of the following simulation model systems: the Weather Research and Forecasting (WRF) model to simulate meteorological fields; the Community Multi-scale Air Quality (CMAQ) modeling system to simulate pollutant concentrations; emissions estimate models; and emission databases. Motor vehicle emissions in Japan are estimated using the Japan Auto-Oil Program (JATOP) vehicle emissions estimate model; anthropogenic emissions from sources other than motor vehicles in Japan are estimated using the Georeference-Based Emission Activity Modeling System (G-BEAMS); and biogenic emissions are estimated using the Model of Emissions of Gases and Aerosols from Nature (MEGAN). The Regional Emission inventory in Asia (REAS) is used for emissions in Asian countries except for Japan. The most prominent feature of our framework is its ability to simulate multi-scale air quality. The framework allows for the simulation of emissions and the dynamic transport of pollutants in heavily polluted urban areas with a maximum resolution of 1 × 1 km, and the long-range transport of pollutants is also taken into account. This framework is used to analyze the impact of future emissions from anthropogenic sources on air quality over the Tokyo metropolitan area. NOx, NMVOC and primary PM2.5 emissions over the Tokyo metropolitan area are estimated to be reduced by 44.5%, 18.1% and 41.7%, respectively, from 2005 to 2020. The simulation predicts that concentrations of NO2 and PM2.5 over the Tokyo metropolitan area will decrease by approximately 30–40% and 15–20%, respectively, during the above period. O3 concentrations significantly increase in winter due to decreased titration by NO, whereas no significant variations are observed in spring and summer. In addition, we analyzed the impact of future long-range transport projected under three emission scenarios provided by REAS. The simulation indicates that future long-range transport will affect concentrations of O3 and PM2.5 over the Tokyo metropolitan area; however, its impact is small compared with that of future anthropogenic emissions in Japan.► A framework for a high resolution, 3-D air quality simulation was developed. ► The performance of the simulation is well over Tokyo. ► The air quality over Tokyo will be improved further by existing regulations. ► Domestic emissions are important over Tokyo as well as the long-range transport.
Keywords: Three-dimensional regional air quality simulation; High resolution; Tokyo metropolitan area; Future prediction; Long-range transport;

Carbonaceous aerosol at a forested and an urban background sites in Southern Finland by M. Aurela; S. Saarikoski; H. Timonen; P. Aalto; P. Keronen; K. Saarnio; K. Teinilä; M. Kulmala; R. Hillamo (1394-1401).
Submicrometer organic carbon (OC) and elemental carbon (EC) concentrations were studied for one year (2007–2008) in Finland at an urban background site (Helsinki) and a forested site (Hyytiälä). Particles were collected on quartz filters that were analyzed by a thermal-optical carbon analyzer in the laboratory. Results were calculated by taking into account the positive sampling artefact and the optical correction for the pyrolysis during the analysis. Typically OC and EC concentrations were higher in Helsinki than in Hyytiälä. OC was highly correlated between the sites, whereas EC had much weaker correlation. There were no clear seasonal variations for OC either in Hyytiälä or in Helsinki, whereas both sites had the lowest EC concentrations in summer. There was a clear summer maximum in OC to EC ratios in Hyytiälä reflecting that biogenic emissions had a considerable influence to OC in summer. Same phenomena could not be seen in Helsinki as there were other major sources (e.g. traffic), which had no seasonal dependency. Traffic had a clear contribution to EC concentrations in Helsinki but in winter there were also other major sources, like residential wood combustion, that affected EC concentrations. Three cases with the high OC concentrations and one case with the low OC concentration in Hyytiälä were studied in detail.► OC was highly correlated between Helsinki and Hyytiälä sites. ► A clear summer maximum in OC to EC ratios in Hyytiälä. ► Local traffic had clear contribution to EC concentrations in Helsinki. ► Also other than traffic sources (e.g. biomass burning) in winter in Helsinki.
Keywords: Carbonaceous aerosol; Organic carbon; Elemental carbon;

Effect of exogenous phosphorus addition on soil respiration in Calamagrostis angustifolia freshwater marshes of Northeast China by Changchun Song; Deyan Liu; Yanyu Song; Guisheng Yang; Zhongmei Wan; Yingchen Li; Xiaofeng Xu (1402-1406).
Anthropogenic activities have increased phosphorus (P) inputs to wetland ecosystems. However, little is known about the effect of P enrichment on soil respiration in these ecosystems. To understand the effect of P enrichment on soil respiration, we conducted a field experiment in Calamagrostis angustifolia-dominated freshwater marshes, the Sanjiang Plain, Northeast China. We investigated soil respiration in the first growing season after P addition at four rates (0, 1.2, 4.8 and 9.6 g P m−2 year−1). In addition, we also examined aboveground biomass, soil labile C fractions (dissolved organic C, DOC; microbial biomass C, MBC; easily oxidizable C, EOC) and enzyme activities (invertase, urease and acid phosphatase activities) following one year of P addition. P addition decreased soil respiration during the growing season. Dissolved organic C in soil pore water increased after P addition at both 5 and 15 cm depths. Moreover, increased P input generally inhibited soil MBC and enzyme activities, and had no effects on aboveground biomass and soil EOC. Our results suggest that, in the short-term, soil respiration declines under P enrichment in C. angustifolia-dominated freshwater marshes of Northeast China, and its extent varies with P addition levels.► In the short-term, soil respiration declined under P enrichment in Calamagrostis angustifolia-dominated freshwater marshes of Northeast China, and its extent varied with P addition levels. ► Dissolved organic C in soil pore water increased after P addition at both 5 and 15 cm depths. ► Increased P input generally inhibited soil microbial biomass C and enzyme activities, and had no effects on aboveground biomass and soil EOC.
Keywords: Aboveground biomass; Dissolved organic C; Microbial biomass C; The Sanjiang Plain; Soil enzyme activities;

Impacts of aerosols on regional meteorology due to Siberian forest fires in May 2003 by Daeok Youn; Rokjin J. Park; Jaein I. Jeong; Byung-Kwon Moon; Sang-Wook Yeh; Young Ho Kim; Jung-Hun Woo; Eul Gyu Im; Jee-Hoon Jeong; Suk-Jo Lee; Chang-Keun Song (1407-1412).
We examine the impacts of aerosols on regional meteorology due to intense Siberian forest fires occurred in May 2003 using both reanalysis data and global model simulations. Our analysis of the NCEP-DOE reanalysis data shows 99% statistical significant changes in meteorological variables over East Asia in May 2003 relative to the 30 years climatology. In particular a significant surface cooling was observed up to −3.5 K over Siberia and extended to the North Pacific region with the surface pressure increases up to 5.6 hPa. Whereas, smoke aerosols affected the large-scale circulations and resulted in the increases in rainfall rates of 2.9 mm day−1 averaged over the NW Pacific (10–35°N, 130–170°E). We use the climate model simulations with and without biomass burning emissions over Siberia to examine the effects of smoke aerosols on the regional meteorology. The simulated results show consistent changes in meteorological variables including surface temperature, surface pressure and precipitation rates with the observations over East Asia and the NW Pacific, which support that the observed changes are likely due to smoke aerosols from the Siberian forest fires. The implication is that smoke aerosols from the forest fires should be properly considered to correctly simulate both regional climate and synoptic scale weather patterns.► Impacts of aerosols from forest fires on regional meteorology were examined in May 2003. ► Direct effects of fire aerosols were found to cause a significant change in regional meteorology. ► Fires affected circulations with implications for regional climate and synoptic weathers.
Keywords: Forest fire aerosols; Regional meteorology; Climate model; Chemistry-transport model;

Vehicle emissions are major precursors for the formation of tropospheric ozone that can have adverse effect on human health, buildings and vegetation. The aim of this study is to investigate the impact of altitude on emission rates of ozone precursors (e.g., CO, NOx and VOCs) from gasoline-driven light–duty commercial vehicles (LDCVs) in three Indian cities (i.e. Delhi, Dehradun, and Mussoorie). Basic equations of the International Vehicle Emission (IVE) model are applied to estimate emission rates from the LDCVs. Topography (altitude) and meteorology (temperature) specific parameters of the IVE model were modified to Indian conditions for estimating emission rates. Unlike NOx, emission rates of CO and VOCs have increased with altitude. For example, CO emission rate has considerably increased from 36.5 g km−1 in Delhi to 51.3 g km−1 (i.e. by ∼41%) in Mussoorie, whereas VOCs emission rate marginally increased from 3.2 g km−1 to 3.6 g km−1. Findings and their implications are important from human health perspective, especially for the people residing in high altitude cities where a peculiar combination of lower oxygen levels and high concentrations of CO and VOCs can adversely affect the public health. Also, increased levels of CO and VOCs at high altitudes may conspicuously influence the chemistry of tropospheric ozone.► Impact of altitude on emission rates of ozone precursors from LDCVs is investigated. ► Altitude dominantly influences CO, VOCs and NOx emissions from LDCVs in hilly areas. ► Unlike NOx, emissions of CO and VOCs increase with increase in altitude. ► Emissions of CO and VOCs were found to be increasing at high ambient temperature. ► Altitude and meteorology should be considered in vehicular emission estimations.
Keywords: Air pollution; Vehicle emission rates; IVE model; Altitude; Temperature; Ozone;

Short-term CO2(g) exchange between a shallow karstic cavity and the external atmosphere during summer: Role of the surface soil layer by S. Cuezva; A. Fernandez-Cortes; D. Benavente; P. Serrano-Ortiz; A.S. Kowalski; S. Sanchez-Moral (1418-1427).
This study tests the hypothesis that the degree of moisture in the soil pore system determines gas exchange processes (ventilation/charge) between the outer atmosphere and the karst-epikarst during the warm, dry period (summer). These processes explain “anomalous” CO2 fluxes measured over this and other ecosystems. Emission of CO2 by ventilation of cavities requires an open double membrane system (host rock and soil) through which air movement can take place (H2Ovapour, CO2, 222Rn, etc.). An experimental study on the behavior of the soil and host rock porous system under changing air humidity conditions, coupled with a broad analytical approach addressing CO2 fluxes using the eddy-covariance technique and monitoring of the cave microclimate serves to define the suitable environmental conditions favoring air transfer between the cave atmosphere and exterior. This study shows the correlation between evapotranspiration, CO2 emissions, and cave ventilation processes due to the daytime opening of the soil membrane. Thus, the role of the soil as a membrane/interface or transfer medium can be observed, and it is directly dependent on weather conditions (temperature, humidity, wind).► Daily episodes of ventilation in caves represent net CO2 emissions to the exterior. ► Emission of CO2 of caves requires an open double membrane system (host rock–soil). ► The soil acts as a barrier limiting gas exchange depending on weather conditions. ► The soil porous system determines the daily cyclic operation of the membrane.
Keywords: Epikarst; Ventilation; Eddy covariance; Soil porosity; Evapotranspiration; Global carbon cycle;

Biomonitoring of PAHs by using Quercus ilex leaves: Source diagnostic and toxicity assessment by Flavia De Nicola; Lancellotti Claudia; Prati MariaVittoria; Maisto Giulia; Alfani Anna (1428-1433).
Quercus ilex L. leaves were sampled at nineteen urban sites and two remote sites in order to evaluate PAH contamination degree. One-, two- and three-year-old leaves were collected and leaf lipid content was measured to investigate the influence of leaf age and lipids in PAH accumulation. Some PAH diagnostic ratios, such as Ant/Ant + Phen, Flt/Flt + Pyr, B[a]A/B[a]A + Crys and IP/IP + B[g,h,i]P, were calculated. The results suggest that Q. ilex leaves are effective biomonitors of PAH air contamination: in fact, a great PAH accumulation in leaves from the urban areas, until 30-time higher compared to those from the remote sites, has been observed. At each site, the similar total PAH concentrations in leaves of different age, probably due to a canopy effect, indicate an ability of all leaf age classes to monitor local PAH concentrations in air, remarking practical implications for air biomonitoring. The findings suggest that PAH adsorption in Q. ilex leaves does not result limited by leaf lipid content. Moreover, this study demonstrates the source-diagnostic potential of Q. ilex leaves, because, in particular, the Flt/Flt + Pyr and IP/IP + B[g,h,i]P ratios indicate vehicular traffic as the main source of PAHs in the urban areas and wood combustion in the remote areas. Moreover, to distinguish biomass combustion source, a promising tracer PAH as DB[a,h]A could be used. The high contribution of DB[a,h]A to total PAH concentrations at the remote sites determines a high carcinogenic potential in this area, similar to that calculated for the urban area where the carcinogenic PAH concentrations in absolute values are often higher.► Spatial distribution of Quercus ilex leaf PAHs as indicative of the contamination degree. ► Assignment of PAH emission sources and assessment of carcinogenic potency. ► Spatial variability of leaf PAH content indicates the feasibility of Q. ilex as biomonitor of PAH contamination. ► The research findings highlight the source-diagnostic potential of Q. ilex leaves. ► In natural areas the toxicity, high as in urban areas, is driven by DB[a,h]A, due to biomass combustion.
Keywords: Leaf age; Leaf lipid; Leaf dry weight; Carcinogenic PAH; PAH diagnostic ratio; Toxic equivalent factor;

Exposure to particle concentrations in urban areas was evaluated in several studies since airborne particles are considered to bring about adverse health effects. Transportation modes and urban microenvironments account for the highest contributions to the overall daily particle exposure concentration.In the present study an evaluation of the influential parameters affecting particle exposure of pedestrian in urban areas is reported. Street geometry, traffic mode, wind speed and direction effects were analyzed through an experimental campaign performed in different streets of an Italian town. To this purpose a high-resolution time measurement apparatus was used in order to capture the dynamic of the freshly emitted particles.Number, surface area and mass concentrations and distributions were measured continuously along both the sides of street canyons and avenue canyons during 10-minutes walking routes. The combined effect of street geometry and wind direction may contribute strongly to dilute the fresh particles emitted by vehicles. In particular, street canyons are characterized by lower ventilation phenomena which lead to similar concentration values on both the side of the street. Higher wind speed was found to decrease concentrations in the canyon. Traffic mode also seems to influence exposure concentrations. In particular, submicrometer particle mass concentration was higher as the traffic is more congested; otherwise, coarse fraction dominates mass exposure concentration along street characterized by a more fluent traffic, showing a typical resuspension modality.► High-resolution time characterization of urban aerosol. ► Evaluation of each influence parameter on pedestrian exposure. ► High peak number concentrations in street canyons with traffic jam. ► Higher mass concentration (resuspension) in streets with fluent traffic conditions. ► Influence of the pedestrian distance (kerb- or building-side) to the traffic emission.
Keywords: Pedestrian exposure; Ultrafine particles; Fast mobility particle sizer; Urban exposure; Street canyon;

Aerosol particles generated by diesel-powered school buses at urban schools as a source of children’s exposure by Heather A. Hochstetler; Mikhail Yermakov; Tiina Reponen; Patrick H. Ryan; Sergey A. Grinshpun (1444-1453).
Various heath effects in children have been associated with exposure to traffic-related particulate matter (PM), including emissions from school buses. In this study, the indoor and outdoor aerosol at four urban elementary schools serviced by diesel-powered school buses was characterized with respect to the particle number concentrations and size distributions as well as the PM2.5 mass concentrations and elemental compositions. It was determined that the presence of school buses significantly affected the outdoor particle size distribution, specifically in the ultrafine fraction. The time-weighted average of the total number concentration measured outside the schools was significantly associated with the bus and the car counts. The concentration increase was consistently observed during the morning drop-off hours and in most of the days during the afternoon pick-up period (although at a lower degree). Outdoor PM2.5 mass concentrations measured at schools ranged from 3.8 to 27.6 μg m−3. The school with the highest number of operating buses exhibited the highest average PM2.5 mass concentration. The outdoor mass concentrations of elemental carbon (EC) and organic carbon (OC) were also highest at the school with the greatest number of buses. Most (47/55) correlations between traffic-related elements identified in the outdoor PM2.5 were significant with elements identified in the indoor PM2.5. Significant associations were observed between indoor and outdoor aerosols for EC, EC/OC, and the total particle number concentration. Day-to-day and school-to-school variations in Indoor/Outdoor (I/O) ratios were related to the observed differences in opening windows and doors, which enhanced the particle penetration, as well as indoor activities at schools. Overall, the results on I/O ratio obtained in this study reflect the sizes of particles emitted by diesel-powered school bus engines (primarily, an ultrafine fraction capable of penetrating indoors).► In this study, the indoor and outdoor aerosol at four urban elementary schools serviced by diesel-powered school buses was characterized with respect to the particle number concentrations and size distributions as well as the PM2.5 mass concentrations and elemental compositions. ► The presence of school buses significantly affected the outdoor particle size distribution, specifically in the ultrafine fraction. ► Significant associations were observed between indoor and outdoor aerosols for EC, EC/OC, and the total particle number concentration.
Keywords: Traffic aerosol; PM2.5; Diesel; School bus; Outdoor; Indoor;

A detailed inventory framework was developed to estimate nitrous oxide (N2O) and methane (CH4) emissions from UK agriculture using the IPCC approach. The inventory framework model was illustrated by combining relevant emission factors with agricultural census data for England, Wales, Scotland and Northern Ireland for the year 2000 to derive country-specific emission estimates which were summed to derive the UK total. The framework enables simple assessment to be made of the impact on national emissions of using different emission factors (EFs) (e.g. site- or local-specific compared with IPCC default factors). The framework was used to calculate the average annual emissions of nitrous oxide (N2O) and methane (CH4) for specific livestock and crops, and amounts lost through volatilisation, leaching and runoff for each country in the UK. The framework provides a simple, realistic and transparent approach to estimating national emissions and can easily be updated.► A detailed inventory to estimate GHGs with much improvement of animal and crop categories. ► Flexible to use either the IPCC default, local-specific or more complex EFs from process-based models. ► Simple, realistic, transparent and global coverage. ► Illustrated using four country data but easy to be extended to higher resolution without any structural change. ► Easy to update and to integrate with GIS for spatial variation and map emissions pattern.
Keywords: Methane; Inventory; Greenhouse gas emissions; Nitrous oxide;

Temporal and spatial variations of nitrous oxide fluxes from the littoral zones of three alga-rich lakes in coastal Antarctica by Yashu Liu; Renbin Zhu; Dawei Ma; Hua Xu; Yuhan Luo; Tao Huang; Liguang Sun (1464-1475).
Nitrous oxide (N2O) fluxes across air–water interface were investigated in the littoral zones of three alga-rich lakes (Lake Mochou, Lake Tuanjie and Lake Daming) in east Antarctica during the summers of 2007/2008 and 2008/2009. In the littoral zones of these three lakes, the mean N2O fluxes were 3.1 ± 6.7 μgN2O–N m−2 h−1, 2.5 ± 2.8 μgN2O–N m−2 h−1 and 7.2 ± 6.9 μgN2O–N m−2 h−1, respectively. The fluxes showed a large temporal and spatial variation in lake littoral zones. On the whole, lake littoral zones were the emission sources for atmospheric N2O although negative fluxes occurred on most of the observation sites. The mean flux significantly correlated with NO3 –N concentration in the sediments at each site, suggesting that spatial variations of N2O fluxes have a connection with NO3 –N concentration. The seasonal pattern of the flux was positively related to daily radiation and air temperature and negatively to water depth, indicating that these factors and alga activity had an important effect on N2O emissions. The summertime N2O budget across air–water interface was estimated to be 6.7 mg N2O–N m−2, 5.4 mg N2O–N m−2 and 15.6 mg N2O–N m−2 from the littoral zones of Lake Mochou, Lake Tuanjie and Lake Daming, respectively. Our results indicated that lake littoral N2O emissions could have a regional importance in coastal Antarctica.► N2O fluxes were investigated in littoral zones of three lakes, east Antarctica. ► N2O fluxes showed a large temporal and spatial variation in lake littoral zones. ► On the whole lake littoral zones were the emission sources for atmospheric N2O. ► Lake littoral N2O emissions could have a regional importance in coastal Antarctica.
Keywords: Nitrous oxide; Lake; Antarctica; Flux; Littoral zone;

This paper presents the simulation and field evaluation results for two mathematical algorithms applied in the horizontal radial plume mapping (HRPM) technique with optical remote sensing instruments. In the simulation study, 450 test maps with skewed distributions (i.e., bivariate lognormal distribution) were generated in a two-dimensional domain. The HRPM techniques with the smooth basis function minimization (SBFM) algorithm and non-negative least square (NNLS) algorithm were then applied to reconstruct the plumes, assuming a nine-beam scanning beam geometry. The SBFM algorithm was able to identify the peak locations better than the NNLS algorithm when the plumes were near the origin. On the other hand, the NNLS performed better when the plumes were away from the origin. In the field validation study, four experiments were conducted in an open space with the same nine-beam geometry. In each experiment, two tracer gases were released simultaneously at two different locations, and an OP-FTIR was set up to collect the IR spectra. The collected path-integrated concentration data were then used to reconstruct the source locations. The results confirm the conclusions obtained in the simulation study of a better performance from the SBFM algorithm than from the NNLS algorithm for plumes near the origin. We also developed a screening criterion to determine which algorithm results should be chosen as the final estimates in future field applications.► We compare two algorithms applied in the horizontal radial plume mapping technique. ► The non pixel-based method should be used for plumes near the origin.► The pixel-based method should be used for plumes away from the origin. ► We develop screening criteria to determine which algorithm results should be chosen.
Keywords: Optical remote sensing; OP-FTIR; Emission source; Air pollutant; Source characterization; Computed tomography;

Sensitivity of contrail coverage and contrail radiative forcing to selected key parameters by C. Frömming; M. Ponater; U. Burkhardt; A. Stenke; S. Pechtl; R. Sausen (1483-1490).
Estimates of global mean radiative forcing of line-shaped contrails are associated with a high level of uncertainty. Recent estimates for present day air traffic range from 5.4 mWm−2 to 25.6 mWm−2. The aim of this research paper is to systematically study the sensitivity of contrail radiative forcing to selected key parameters and to highlight the most important factors for this large uncertainty range, while employing an improved version of the ECHAM climate model.The dominating parameters on contrail radiative forcing are found to be the detection threshold used for calibrating contrail coverage to observations, and the mean optical depth. Assuming a detection threshold of 0.05 instead of 0.02 yields an increase of the total coverage, resulting in a 146% increase of global mean contrail radiative forcing. Employing a globally constant optical depth of up to 0.3, increases the net radiative forcing by 140% over the reference case which has a mean optical depth of 0.08. An upgraded parameterisation of potential contrail coverage yields a significantly larger amount of tropical contrails, increasing the contrail radiative forcing by 53%. The calibration to an alternative observation region along with the assumption of a higher visibility threshold yields an increase of the radiative forcing by 46%. Moderate sensitivity of global contrail radiative forcing (∼15%) is found for an improvement of model climate and for changes in particle shape. The air traffic inventory, air traffic density parameter, and the diurnal variation of air traffic have only a small effect on global and annual mean contrail radiative forcing, but their influence on regional and seasonal contrail radiative forcing may nevertheless be important.► Important parameters for the sensitivity of global contrail radiative forcing are: ► The detection threshold for calibrating contrail coverage to observations. ► The mean optical depth. ► An upgraded parameterisation of potential contrail coverage. ► The observation region used for calibration. ► An upgraded model version featuring improved model climate and the contrail particle shape.
Keywords: Air traffic; Aviation; Climate impact; Contrail coverage; Radiative forcing; Optical depth;

Precautions for in-injection port thermal desorption-gas chromatography/mass spectrometry (TD-GC/MS) as applied to aerosol filter samples by Steven Sai Hang Ho; Judith C. Chow; John G. Watson; Louisa Pan Ting Ng; Yuk Kwok; K.F. Ho; Junji Cao (1491-1496).
In-injection port thermal desorption-gas chromatography/mass spectrometry (TD-GC/MS) allows for analysis for >130 non-polar organic compounds on small quartz-fiber filter samples without extraction chemicals. TD-GC/MS has been applied to samples from long-term U.S. networks since it is cost effective and less labor intensive. However, analysis of large numbers of samples results in sensitivity reductions over time. Instrument sensitivity and reproducibility were examined after 100, 200, and 500 sample analyses. Analyses of standards between batches of heavily loaded samples from China and Japan showed signal decreases of 28–78% for major organic classes. In the GC injection port, residues can accumulate on the gold-plated seal resulting in analyte adsorption as well as elevating signal background. Decreases in signal response were 28–43% for n-alkanes, 33–45% for hopanes and steranes, 28–56% for PAHs, and 38–78% for phthalates when the gold-plated seal was not replaced after 500 TD-GC/MS sample analyses. Limits of detection (LODs) also increased by 14–76% for the targeted non-polar organic compounds. Residues trapped in the capillary column head can cause peak broadening and overlap. The GC/MS system, including the injection port and gold seal, the column head (where the eluted sample is pre-concentrated), and the ion source should be cleaned after every batch of 50–100 samples.
Keywords: Thermal desorption; In-injection port; GC/MS; Non-polar organic; PAHs; Alkanes; Phthalates;