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Estimates of the radiative forcing due to anthropogenically-produced tropospheric O<sub>3</sub> are derived primarily from models. Here, we use tropospheric ozone and cloud data from several instruments in the A-train constellation of satellites as well as information from the GEOS-5 Data Assimilation System to accurately estimate the radiative effect of tropospheric O<sub>3</sub> for January and July 2005. Since we cannot distinguish between natural and anthropogenic sources with the satellite data, our derived radiative effect reflects the unadjusted (instantaneous) effect of the total tropospheric O<sub>3</sub> rather than the anthropogenic component. We improve upon previous estimates of tropospheric ozone mixing ratios from a residual approach using the NASA Earth Observing System (EOS) Aura Ozone Monitoring Instrument (OMI) and Microwave Limb Sounder (MLS) by incorporating cloud pressure information from OMI. We focus specifically on the magnitude and spatial structure of the cloud effect on both the short- and long-wave radiative budget. The estimates presented here can be used to evaluate the various aspects of model-generated radiative forcing. For example, our derived cloud impact is to reduce the radiative effect of tropospheric ozone by ~16%. This is centered within the published range of model-produced cloud effect on unadjusted ozone radiative forcing.
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Stable atmospheric conditions are often connected with the occurrence of high pollution episodes especially in urban or industrial areas. In this work we investigate a severe SO<sub>2</sub> episode observed on 3–5 February 2002 in a coastal industrial town of Rijeka, Croatia, where very high daily mean concentrations (up to 353.5 μg m<sup>−3</sup>) were measured. The episode occurred under high air pressure conditions, which were accompanied with a fog and low wind speeds. Three air quality models (50-km EMEP model, 10-km EMEP4HR model and 1-km CAMx model) were used to simulate SO<sub>2</sub> concentrations fields and to evaluate the relative contribution of distant and local pollution sources to observed concentrations. Results suggest that the episode was caused predominately by local sources. Furthermore, using three-dimensional, higher-order turbulence closure mesoscale meteorological model (WRF), the wind regimes and thermo-dynamical structure of the lower troposphere above the greater Rijeka area (GRA) were examined in detail. Modelled atmospheric fields suggest several factors whose simultaneous acting was responsible for elevated SO<sub>2</sub> concentrations. Established small scale wind directions supported the transport of air from nearby industrial areas with major pollution sources towards Rijeka. This transport was associated with strong, ground-based temperature inversion and correspondingly, very low mixing layer (at most up to about 140 m). Additionally, the surface winds in Rijeka were light or almost calm thus, preventing ventilation of polluted air. Finally, a vertical circulation cell formed between the mainland and a nearby island, supported the air subsidence and the increase of static stability.
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Glyoxal, CHO.CHO, is produced during the oxidation of volatile organic compounds, VOC, released by anthropogenic activities, biogenic processes and biomass burning. It has a short chemical lifetime of a few hours in the boundary layer and lower troposphere and therefore serves as an indicator and a marker of photochemical hot-spots and their response to changing atmospheric conditions around the globe. For this reason more than five years of CHO.CHO observations (2002–2007), retrieved from the radiances measured by the satellite instrument SCIAMACHY, were obtained and analyzed both temporally and spatially. The largest columns of CHO.CHO (>6.10<sup>14</sup> molec cm<sup>−2</sup>) are found in the tropical and sub-tropical regions, associated with high biological activity and the plumes from vegetation fires. The majority of the identified hot spots are characterized by a well-defined seasonality: the highest values being observed during the warm and dry periods as a result of the enhanced biogenic, primarily isoprene, emissions and/or biomass burning from natural or man-made fires. The regions influenced by anthropogenic pollution also encounter enhanced amounts of glyoxal. The ratio "CHO.CHO to HCHO, R<sub><I>GF</I></sub>" over the biogenically influenced photochemical hot-spots is approximately 0.045. For the studied regions, the presence of pyrogenic and anthropogenic emissions increases and decreases this number respectively. Although the 2002–2007 period of observation is limited, over the northeastern Asia a significant annual increase in CHO.CHO in addition to a seasonal cycle is reported.
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Sulphate distributions were simulated with a global chemistry transport model. A chemical scheme describing the sulphur cycle and the parameterisations of the main sinks for sulphate aerosols were included in the model. A six-year simulation was conducted from the years 2000 to 2005, driven by the ECMWF operational analyses. Emissions come from an inventory representative of the year 2000. This paper focuses on the analysis of the sulphate sinks and sources over Europe for the entire period of simulation. The Sulphate burden shows a marked annual cycle, which is the result of the annual variations of the aqueous and gaseous chemistry. Regionally, the monthly mean aerosol burden can vary by a factor of 2 from one year to another, because of different weather conditions, driving chemistry, transport and wet deposition of sulphate aerosols. Sulphate ground concentrations, scavenging fluxes and precipitation modelled were compared with observations. The model represents quite well sulphate fields over Europe, but has a general tendency to overestimate sulphate ground concentrations, in particular over Northern Europe. We assume that it is linked to the representation of the scavenging fluxes, which are underestimated. We suggest that uncertainties in modelled precipitation explain only partially the underestimation of the scavenging fluxes in the model.
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Indoor and outdoor water soluble trace elements (TEs) were analyzed on quasi-ultrafine (UF), accumulation, and coarse PM filter samples collected at four retirement communities, three located in the San Gabriel Valley and one in Riverside, CA. Our analysis indicates that a complex mix of vehicular, industrial, and soil-related emissions was responsible for the elemental concentrations measured at the three San Gabriel sites, while regional transport, soil re-suspension and, to a lower degree, local traffic contributed to TE levels observed in Riverside. In the quasi-UF mode, the magnitude of indoor/outdoor concentration ratios (I/O) for elements of anthropogenic origin was highly variable, reflecting the spatial heterogeneity of combustion sources in the study area. Indoor/outdoor ratios in accumulation mode PM were closer to 1, and more homogeneous across sites, indicating that elements associated with this size fraction penetrate indoors with high efficiencies. The lowest overall I/O ratios were obtained for elements found in coarse particles, consistent with the fact that only a small portion of coarse outdoor PM infiltrates indoors. The potential of S and other TEs to serve as tracers of indoor-penetrated particles of outdoor origin was also examined. Our results suggest that using the I/O ratio of S (I/O<sub>S</sub>) as a surrogate of the infiltration factor for PM<sub>2.5</sub> [Finf(PM<sub>2.5</sub>)] might lead to an overestimation of the indoor PM<sub>2.5</sub> originating outdoors. This is in contrast with what was reported in previous studies conducted in the Eastern US, where S has been consistently used as a reliable tracer of outdoor PM<sub>2.5</sub> infiltrating indoors. Our differences may be due to the fact that in the Los Angeles basin (and in general in the Western US) PM<sub>2.5</sub> includes a number of semi-volatile labile species, such as ammonium nitrate and several organic compounds, which volatilize either entirely or to a substantial degree upon building entry.
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A coupled box model of photochemistry and aerosol microphysics which explicitly accounts for size-dependent chemical properties of the condensed-phase has been developed to simulate the multi-phase chemistry of chlorine, bromine and iodine in the marine boundary layer (MBL). The model contains separate seasalt and non-seasalt modes, each of which may be composed of 1–16 size-bins. By comparison of gaseous and aerosol compositions predicted using different size-resolutions with both fixed and size-dependent aerosol turnover rates, it was found that, for halogen-activation processes, the physical property initialisation of the aerosol-mode has a significant influence on gas-phase chemistry. Failure to adequately represent the appropriate physical properties can lead to substantial errors in gas-phase chemistry. The size-resolution of condensed-phase composition has a less significant influence on gas-phase chemistry.
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A full year of measurements of surface ozone over the Arctic Ocean far removed from land is presented (81° N–88° N latitude). The data were obtained during the drift of the French schooner TARA between September 2006 and January 2008, while frozen in the Arctic Ocean. The data confirm that long periods of virtually total absence of ozone occur in the spring (mid March to mid June) after Polar sunrise. At other times of the year, ozone concentrations are comparable to other oceanic observations with winter mole fractions of ca. 30–40 nmol mol<sup>−1</sup> and summer minima of ca. 20 nmol mol<sup>−1</sup>. Contrary to earlier observations from ozone sonde data obtained at Arctic coastal observatories, the ambient temperature was well above −20°C during most ODEs (ozone depletion episodes). Backwards trajectory calculations suggest that during these ODEs the air had previously been in contact with the frozen ocean surface for several days and originated largely from the Siberian coast where several large open flaw leads and polynyas developed in the spring of 2007.
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This study originated from recent results reported in literature, which support the existence of long-range (power-law) persistence in atmospheric temperature fluctuations on monthly and inter-annual scales. We investigated the results of Detrended Fluctuation Analysis (DFA) carried out on twenty-two historical daily time series recorded in Europe in order to evaluate the reliability of such findings in depth. More detailed inspections emphasized systematic deviations from power-law and high statistical confidence for functional form misspecification. Rigorous analyses did not support scale-free correlation as an operative concept for Climate modelling, as instead suggested in literature. In order to understand the physical implications of our results better, we designed a bivariate Markov process, parameterised on the basis of the atmospheric observational data by introducing a slow dummy variable. The time series generated by this model, analysed both in time and frequency domains, tallied with the real ones very well. They accounted for both the deceptive scaling found in literature and the correlation details enhanced by our analysis. Our results seem to evidence the presence of slow fluctuations from another climatic sub-system such as ocean, which inflates temperature variance up to several months. They advise more precise re-analyses of temperature time series before suggesting dynamical paradigms useful for Climate modelling and for the assessment of Climate Change.
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Results of an experimental campaign that took place in the greater Thessaloniki area were used to investigate temporal and spatial UV variability within an OMI satellite pixel. UV irradiance and aerosol optical depth measurements were performed for a one month period at three sites characterized as urban, rural and industrial, depending on their location and possible local aerosol sources. OMI showed a general UV irradiance overestimation compared to all three sites and for all atmospheric conditions. During the campaign the standard deviation calculated from the three sites for UV irradiance at 324 nm was of the order of 26%. For cloudless days with high spatial aerosol variability, UV differences reached ±20% within the OMI pixel. For cloudy days UV differences up to 100% were found at the three sites, a percentage that depends on the ground-based data integration time used for the comparison. Here we tried to focus on the limitations when trying to interpret results of UV irradiance comparisons between OMI satellite and ground based stations, taking into account the UV variability within an OMI pixel, due to such small scale spatial cloud and aerosol inhomogeneities.
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The main objective of this study is the identification of major factors controlling levels and chemical composition of aerosols in the regional background (RB) along the Mediterranean Basin (MB). To this end, data on PM levels and speciation from Montseny (MSY, NE Spain), Finokalia (FKL, Southern Greece) and Erdemli (ERL, Southern Turkey) for the period 2001 to 2008 are evaluated. Important differences on PM levels and composition are evident when comparing the Western and Eastern MBs. The results manifest W-E and N-S PM<sub>10</sub> and PM<sub>2.5</sub> gradients along the MB, attributed to the higher frequency and intensity of African dust outbreaks in the EMB, while for PM<sub>1</sub> very similar levels are encountered. <br><br> PM in the EMB is characterized by higher levels of crustal material and sulphate as compared to WMB (and central European sites), however, RB nitrate and OC + EC levels are relatively constant across the Mediterranean and lower than other European sites. Marked seasonal trends are evidenced for PM levels, nitrate (WMB), ammonium and sulphate. Also relatively higher levels of V and Ni (WMB) are measured in the Mediterranean basin, probably as a consequence of high emissions from fuel-oil combustion (power generation, industrial and shipping emissions). <br><br> Enhanced sulphate levels in EMB compared to WMB were measured. The high levels of sulphate in the EMB may deplete the available gas-phase NH<sub>3</sub> so that little ammonium nitrate can form due to the low NH<sub>3</sub> levels. <br><br> This study illustrates the existence of three very important features within the Mediterranean that need to be accounted for when modeling climate effects of aerosols in the area, namely: a) the increasing gradient of dust from WMB to EMB; b) the change of hygroscopic behavior of mineral aerosols (dust) via nitration and sulfation; and c) the abundance of highly hygroscopic aerosols during high insolation (low cloud formation) periods.
