Residence Time Of Air Masses Research Articles

Utilizing innovative input data and ANN modeling to predict atmospheric gross beta radioactivity in Spain

This study introduces a new methodology aimed at predicting gross β levels in the atmosphere. The methodology incorporates input data consisting of local meteorological and synoptic variables, alongside temporal lags and residence time of air masses, to predict gross β activity concentration in the atmosphere. Weekly measurements conducted between January 2006 and December 2017 at various sampling sites across diverse locations with different climatic and geographical conditions in Spain were utilized. A high-performance Artificial Neural Network (ANN) model was constructed for this purpose. Across all locations, strong linear relationships are evident between predicted and actual values, with correlation coefficients (R) ranging from 0.86 to 0.92. Higher R values indicate a more robust correlation. Additionally, R-squared values, ranging from 0.7320 to 0.8502, further affirm the model’s ability to explain a significant proportion of the variance in gross β activity. Moreover, the relatively low Mean Squared Error (MSE) values, spanning from 0.00966 to 0.11115, and Mean Absolute Error (MAE) values, ranging from 0.08176 to 0.11747, underscore the model’s accuracy in gross β activity prediction. The predictive capabilities of the models are robustly demonstrated, showcasing promising results. According to the results of the sensitivity analysis, the category of synoptic parameters has the most important influence on the prediction of atmospheric β radioactivity levels, namely air temperature, potential temperature and relative humidity. Regarding the residence time of the air masses, the periods spent over land or water have the most effect on gross β levels.

Intra- and inter-city variability of PM2.5 concentrations in Greece as determined with a low-cost sensor network

Measurements of PM2.5 concentrations in five major Greek cities over a two-year period using calibrated low-cost sensor-based particulate matter (PM) monitors (Purple Air PA-II) were combined with local meteorological parameters, synoptic patterns and air mass residence time models to investigate the factors controlling PM2.5 spatiotemporal variability over continental Greece. Fourteen sensors nodes in Athens, Patras, Ioannina, Xanthi, and Thermi (in the Metropolitan Area of Thessaloniki) were selected out of more than 100 of a countrywide network for detailed analysis. The cities have populations ranging from 65k to 3M inhabitants and cover different latitudes along the South-North axis. High correlations between the daily average PM2.5 levels were observed among all sites, indicating strong intra- and inter-city covariance of concentrations, both in cold and warm periods. Higher PM2.5 concentrations in all cities during the cold period were primarily associated with low temperatures and stagnant anticyclonic conditions, favoring the entrapment of residential heating emissions from biomass burning. Anticyclonic conditions were also connected to an increased frequency of PM2.5 episodes, exceeding the updated daily guideline value (15 μg m−3) of the World Health Organization (WHO). During the warm period, nearly uniform PM2.5 levels were encountered across continental Greece, independently of their population size. This uniformity strongly suggests the importance of long-range transport and regional secondary aerosol formation for PM2.5 during this period. Peak concentrations were associated mainly with regional northern air flows over Greece and the Balkan Peninsula. The use of the measurements from dense air quality sensor networks, provided that a robust calibration protocol and continuous data quality assurance practices are followed, appears to be an efficient tool to gain insights on the levels and variability of PM2.5 concentrations, underpinning the characterization of spatial and seasonal particularities and supporting real-time public information and warning.

On the processes governing the variability of PTR-MS based VOCs and OVOCs in different seasons of a year over hillocky mega city of India

The rapidly increasing industrialization and urbanization, in combination with under representation of in-situ measurements, especially Volatile Organic Compounds (VOCs), has posed serious challenges in understanding air quality and atmospheric chemistry over India. Here we present yearlong measurements of VOCs, carried out during March 2014–February 2015 using a Proton Transfer Reaction Mass Spectrometer (PTR-MS) from an urban site Pune (18.58oN, 73.91°E, 559 m amsl) in western tropical India. The averaged diurnal variation in VOCs at Pune exhibited a characteristic bimodal pattern, with highly pronounced peak during morning hours and secondary enhancement during late evening/night, except for Isoprene. Isoprene mixing ratios were observed to be higher (1.30 ± 0.69 ppbv) during the daytime (0900–1800 h) and lower (0.89 ± 0.65 ppbv) during the nighttime (after 1900 h and before 0900 h). While, Methanol, Acetonitrile, and Acetaldehyde are observed to be the highest (14.3 ± 5.9, 0.9 ± 0.4, and 6.1 ± 2.6 ppbv respectively) during spring, Benzene and Toluene were highest (1.6 ± 1.1, 2.6 ± 2.2 ppbv respectively) during winter. Isoprene mixing ratios showed broader maxima during autumn and winter (1.3 ppbv). Nominally, all the VOCs were observed to be lowest during the monsoon season. The two peaks in the seasonal cycle of acetonitrile along with VIIRS retrieved fire counts indicated impact of the regional biomass burning during spring and winter. Analysis of air-mass residence time further revealed potential influences from the highly polluted Indo-Gangetic Plain during the autumn and winter, whereas local pollution supplemented with regional biomass burning found to be the dominant process during spring. These yearlong measurements are a step forward in filling a major gap of observational data of VOCs over the tropical Indian region, which would be invaluable for evaluation of chemistry transport models and understanding of regional tropospheric chemistry.

Chemical composition and source attribution of sub-micrometre aerosol particles in the summertime Arctic lower troposphere

Abstract. Aerosol particles impact the Arctic climate system both directly and indirectly by modifying cloud properties, yet our understanding of their vertical distribution, chemical composition, mixing state, and sources in the summertime Arctic is incomplete. In situ vertical observations of particle properties in the high Arctic combined with modelling analysis on source attribution are in short supply, particularly during summer. We thus use airborne measurements of aerosol particle composition to demonstrate the strong contrast between particle sources and composition within and above the summertime Arctic boundary layer. In situ measurements from two complementary aerosol mass spectrometers, the Aircraft-based Laser Ablation Aerosol Mass Spectrometer (ALABAMA) and an Aerodyne high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS), are presented alongside black carbon measurements from an single particle soot photometer (SP2). Particle composition analysis was complemented by trace gas measurements, satellite data, and air mass history modelling to attribute particle properties to particle origin and air mass source regions. Particle composition above the summertime Arctic boundary layer was dominated by chemically aged particles, containing elemental carbon, nitrate, ammonium, sulfate, and organic matter. From our analysis, we conclude that the presence of these particles was driven by transport of aerosol and precursor gases from mid-latitudes to Arctic regions. Specifically, elevated concentrations of nitrate, ammonium, and organic matter coincided with time spent over vegetation fires in northern Canada. In parallel, those particles were largely present in high CO environments (> 90 ppbv). Additionally, we observed that the organic-to-sulfate ratio was enhanced with increasing influence from these fires. Besides vegetation fires, particle sources in mid-latitudes further include anthropogenic emissions in Europe, North America, and East Asia. The presence of particles in the Arctic lower free troposphere, particularly sulfate, correlated with time spent over populated and industrial areas in these regions. Further, the size distribution of free tropospheric particles containing elemental carbon and nitrate was shifted to larger diameters compared to particles present within the boundary layer. Moreover, our analysis suggests that organic matter, when present in the Arctic free troposphere, can partly be identified as low molecular weight dicarboxylic acids (oxalic, malonic, and succinic acid). Particles containing dicarboxylic acids were largely present when the residence time of air masses outside Arctic regions was high. In contrast, particle composition within the marine boundary layer was largely driven by Arctic regional processes. Air mass history modelling demonstrated that alongside primary sea spray particles, marine biogenic sources contributed to secondary aerosol formation via trimethylamine, methanesulfonic acid, sulfate, and other organic species. Our findings improve our knowledge of mid-latitude and Arctic regional sources that influence the vertical distribution of particle chemical composition and mixing state in the Arctic summer.

Atmospheric deposition of 7Be, 210Pb and 210Po during typhoons and thunderstorm in Shanghai, China and global data synthesis

Atmospherically-delivered 7Be, 210Po and 210Pb in bulk precipitation and air samples collected around the globe have provided valuable quantification on the rates of removal, as well as proportional mixing of attendant air masses; however, such studies during thunderstorm and typhoon events are limited. We report the first continuous time-series rainwater sampling and analysis of 7Be, 210Pb and 210Po from two typhoons and one thunderstorm during 2015 summer in Shanghai. The depositional fluxes within individual rain events of typhoons and thunderstorms varied by a factor of 10 for 7Be, 5.7 for 210Pb, 7.4 for 210Po, and 7.0 for 7Be/210Pb activity ratios (AR). Such large observed variations in the depositional fluxes of 7Be, 210Pb, 210Po and 7Be/210Pb activity ratios were attributed to air masses injected from surrounding high pressure system adjoining the typhoon to low pressure system within the typhoon. Based on 7Be/210Pb activity ratios, we estimated the variations in the fraction of maritime and continental air masses into the typhoon. Observed constancy in the 210Po/210Pb AR indicates that the residence times of air masses contributing to the typhoon during heavy rain are similar. From a synthesis of global fallout of 7Be and 210Pb during pulse events (precipitation≥50 mm from single rainout event), we quantify the importance of pulse events in the atmospheric fallout of these radionuclides.

Ozone and carbon monoxide observations over open oceans on R/V <i>Mirai</i> from 67° S to 75° N during 2012 to 2017: testing global chemical reanalysis in terms of Arctic processes, low ozone levels at low latitudes, and pollution transport

Abstract. Constraints from ozone (O3) observations over oceans are needed in addition to those from terrestrial regions to fully understand global tropospheric chemistry and its impact on the climate. Here, we provide a large data set of ozone and carbon monoxide (CO) levels observed (for 11 666 and 10 681 h, respectively) over oceans. The data set is derived from observations made during 24 research cruise legs of R/V Mirai during 2012 to 2017, in the Southern, Indian, Pacific, and Arctic oceans, covering the region from 67∘ S to 75∘ N. The data are suitable for critical evaluation of the over-ocean distribution of ozone derived from global atmospheric chemistry models. We first give an overview of the statistics in the data set and highlight key features in terms of geographical distribution and air mass type. We then use the data set to evaluate ozone mixing ratio fields from the tropospheric chemistry reanalysis version 2 (TCR-2), produced by assimilating a suite of satellite observations of multiple species into a global atmospheric chemistry model, namely CHASER. For long-range transport of polluted air masses from continents to the oceans, during which the effects of forest fires and fossil fuel combustion were recognized, TCR-2 gave an excellent performance in reproducing the observed temporal variations and photochemical buildup of O3 when assessed from ΔO3∕ΔCO ratios. For clean marine conditions with low and stable CO mixing ratios, two focused analyses were performed. The first was in the Arctic (> 70∘ N) in September every year from 2013 to 2016; TCR-2 underpredicted O3 levels by 6.7 ppbv (21 %) on average. The observed vertical profiles from O3 soundings from R/V Mirai during September 2014 had less steep vertical gradients at low altitudes (> 850 hPa) than those obtained by TCR-2. This suggests the possibility of a more efficient descent of the O3-rich air from above than assumed in the models. For TCR-2 (CHASER), dry deposition on the Arctic ocean surface might also have been overestimated. In the second analysis, over the western Pacific equatorial region (125–165∘ E, 10∘ S to 25∘ N), the observed O3 level more frequently decreased to less than 10 ppbv in comparison to that obtained with TCR-2 and also those obtained in most of the Atmospheric Chemistry Climate Model Intercomparison Project (ACCMIP) model runs for the decade from 2000. These results imply loss processes that are unaccounted for in the models. We found that the model's positive bias positively correlated with the daytime residence times of air masses over a particular grid, namely 165–180∘ E and 15–30∘ N; an additional loss rate of 0.25 ppbv h−1 in the grid best explained the gap. Halogen chemistry, which is commonly omitted from currently used models, might be active in this region and could have contributed to additional losses. Our open data set covering wide ocean regions is complementary to the Tropospheric Ozone Assessment Report data set, which basically comprises ground-based observations and enables a fully global study of the behavior of O3.

Air Mass Trajectories to Estimate the “Most Likely” Areas to Be Affected by the Release of Hazardous Materials in the Atmosphere—Feasibility Study

Countries continuously review and improve their Emergency Preparedness and Response (EP&R) arrangements and capabilities to take agile and rapid actions with the intent of minimizing health, environmental and economic impacts of potential harmful releases into the atmosphere. One of the specific topics within the EP&R field is the estimation of the areas that might be affected. A proposal is presented to estimate the spatial distribution of the released material. The methodology combines the computation of air mass trajectories and the elaboration of density maps from the corresponding end-point positions. To this purpose, density maps are created in a three-way procedure; first, forward trajectories are calculated from a certain location and for a long period of time, e.g., a decade; second, the selected end-point positions are aggregated in a density field by applying the kernel density estimation method, and then the density field is visualized. The final product reports the areas with the longest residence time of air masses, and hence, the areas “most likely” to be affected and where the deposit may be substantial. The usefulness of this method is evaluated taking as reference a ten-year period (2007–2016) and against two different radioactive release scenarios, such as the Chernobyl accident and the Algeciras release. While far from being fully comprehensive, as only meteorological data are used, the performance of this method is reasonably efficient, and hence, it is a desirable alternative to estimating those areas potentially affected by a substantial deposit following the releases of a harmful material in the atmosphere.

Evidence for marine biogenic influence on summertime Arctic aerosol

AbstractWe present vertically resolved observations of aerosol composition during pristine summertime Arctic background conditions. The methansulfonic acid (MSA)‐to‐sulfate ratio peaked near the surface (mean 0.10), indicating a contribution from ocean‐derived biogenic sulfur. Similarly, the organic aerosol (OA)‐to‐sulfate ratio increased toward the surface (mean 2.0). Both MSA‐to‐sulfate and OA‐to‐sulfate ratios were significantly correlated with FLEXPART‐WRF‐predicted air mass residence time over open water, indicating marine‐influenced OA. External mixing of sea salt aerosol from a larger number fraction of organic, sulfate, and amine‐containing particles, together with low wind speeds (median 4.7 m s−1), suggests a role for secondary organic aerosol formation. Cloud condensation nuclei concentrations were nearly constant (∼120 cm−3) when the OA fraction was <60% and increased to 350 cm−3 when the organic fraction was larger and residence times over open water were longer. Our observations illustrate the importance of marine‐influenced OA under Arctic background conditions, which are likely to change as the Arctic transitions to larger areas of open water.

Sources and formation mechanisms of carbonaceous aerosol at a regional background site in the Netherlands: insights from a year-long radiocarbon study

Abstract. We measured the radioactive carbon isotope 14C (radiocarbon) in various fractions of the carbonaceous aerosol sampled between February 2011 and March 2012 at the Cesar Observatory in the Netherlands. Based on the radiocarbon content in total carbon (TC), organic carbon (OC), water-insoluble organic carbon (WIOC), and elemental carbon (EC), we estimated the contribution of major sources to the carbonaceous aerosol. The main source categories were fossil fuel combustion, biomass burning, and other contemporary carbon, which is mainly biogenic secondary organic aerosol material (SOA). A clear seasonal variation is seen in EC from biomass burning (ECbb), with lowest values in summer and highest values in winter, but ECbb is a minor fraction of EC in all seasons. WIOC from contemporary sources is highly correlated with ECbb, indicating that biomass burning is a dominant source of contemporary WIOC. This suggests that most biogenic SOA is water soluble and that water-insoluble carbon stems mainly from primary sources. Seasonal variations in other carbon fractions are less clear and hardly distinguishable from variations related to air mass history. Air masses originating from the ocean sector presumably contain little carbonaceous aerosol from outside the Netherlands, and during these conditions measured carbon concentrations reflect regional sources. In these situations absolute TC concentrations are usually rather low, around 1.5 µg m−3, and ECbb is always very low ( ∼ 0.05 µg m−3), even in winter, indicating that biomass burning is not a strong source of carbonaceous aerosol in the Netherlands. In continental air masses, which usually arrive from the east or south and have spent several days over land, TC concentrations are on average by a factor of 3.5 higher. ECbb increases more strongly than TC to 0.2 µg m−3. Fossil EC and fossil WIOC, which are indicative of primary emissions, show a more moderate increase by a factor of 2.5 on average. An interesting case is fossil water-soluble organic carbon (WSOC, calculated as OC-WIOC), which can be regarded as a proxy for SOA from fossil precursors. Fossil WSOC has low concentrations when regional sources are sampled and increases by more than a factor of 5 in continental air masses. A longer residence time of air masses over land seems to result in increased SOA concentrations from fossil origin.

Influence of quarry mining dust on PM2.5 in a city adjacent to a limestone quarry: Seasonal characteristics and source contributions

To understand the influence of quarry mining dust on particulate matter, ambient PM2.5 and quarry mining dust source samples were collected in a city near quarry facilities during 2013–2014. Samples were subject to chemical analysis for dust-related species (Al, Si, Ca, Fe, Ti), tracer metals, carbon components and water-soluble ions. Seasonal variations of PM2.5 and its main chemical components were investigated. Distinctive seasonal variations of PM2.5 were observed, with the highest PM2.5 concentrations (112.42μgm−3) in fall and lowest concentrations in summer (45.64μgm−3). For dust-related species, mass fractions of Si and Al did not show obvious seasonal variations, whereas Ca presented higher fractions in spring and summer and lower fractions in fall and winter. A combined receptor model (PMF-CMB) was applied to quantify the quarry mining dust contribution to PM2.5. Seven sources were identified, including quarry mining dust, soil dust, cement dust, coal combustion vehicles, secondary sulfate and secondary nitrate. On a yearly average basis, the contribution of quarry mining dust to PM2.5 was 6%. The contribution of soil dust to PM2.5 was comparable with cement dust (13% and 13%, respectively). Other identified sources included vehicle, secondary sulfate, secondary nitrate and coal combustion, which contributed 23, 15, 9 and 18% of the total mass, respectively. Air mass residence time (AMRT) analysis showed that northeast and southeast regions might be the major PM2.5 source during the sampling campaign. The findings of this study can be used to understand the characteristics of quarry mining dust and control strategies for PM2.5.

Influences of regional pollution and long range transport over Hyderabad using ozone data from MOZAIC

Long-term (2005–2011) MOZAIC (Measurements of OZone and water vapor by Airbus In-Service air Craft) ozone data have been investigated over Hyderabad (17.37° N, 78.47°E, 489 m amsl), India using back-air trajectories and contribution from regional pollution and long-range transport are assessed. Ozone data are grouped and analysed according to the air-mass residence time over the central India, marine region and Africa/Middle East regions. Ozone shows a linear dependence on air-mass residence time over the central India region for about six days. Rate of ozone increase is maximum during summer (boundary layer 6.8 ± 0.9 ppbv/day, lower free troposphere 2.4 ± 0.4 ppbv/day) and minimum during winter (boundary layer 1.5 ± 0.2 ppbv/day, lower free troposphere 0.8 ± 0.7 ppbv/day). The background ozone is estimated by extrapolating the linear regression line to zeroth residence day and is found to be significantly lower during summer/monsoon (15.8 ± 2.4 ppbv) within the boundary layer due to influence of marine air-mass. Monthly variation of the boundary layer ozone shows a distinct peak during March–April months. Simultaneous investigation of fire counts and potential source contribution function analysis confirms that Indo-Gangetic Plain (IGP) outflow has a significant contribution in ozone enhancement over even at this southern region throughout the year except in summer-monsoon season. The ozone in regionally polluted air masses influenced by the central Indian region is found to be higher than average ozone by 6–15% within the boundary layer and by 5–9% in the lower troposphere during different seasons. The marine air shows a lower ozone level by 4–28 ppbv throughout the year within the boundary layer. Role of long-range transport from Africa/Middle East is found to be significant in the lower troposphere and shows 4.4 ppbv and 9 ppbv higher ozone mixing ratio during summer and autumn, respectively.

Chemical characteristics of long-range-transported fine particulate matter at Gosan, Jeju Island, in the spring and fall of 2008, 2009, 2011, and 2012

Carbonaceous species (organic carbon [OC] and elemental carbon [EC]) and inorganic ions of particulate matter less than 2.5 μm (PM2.5) were measured to investigate the chemical characteristics of long-range-transported (LTP) PM2.5 at Gosan, Jeju Island, in Korea in the spring and fall of 2008–2012 (excluding 2010). On average, the non-sea-salt (nss) sulfate (4.2 µg/m3) was the most dominant species in the spring, followed by OC (2.6 µg/m3), nitrate (2.1 µg/m3), ammonium (1.7 µg/m3), and EC (0.6 µg/m3). In the fall, the nss-sulfate (4.7 µg/m3) was also the most dominant species, followed by OC (4.0 µg/m3), ammonium (1.7 µg/m3), nitrate (1.1 µg/m3), and EC (0.7 µg/m3). Both sulfate and OC were higher in the fall than in the spring, possibly due to more common northwest air masses (i.e., coming from China and Korea polluted areas) and more frequent biomass burnings in the fall. There was no clear difference in the EC between the spring and fall. The correlation between OC and EC was not strong; thus, the OC measured at Gosan was likely transported across a long distance and was not necessarily produced in a manner similar to the EC. Distinct types of LTP events (i.e., sulfate-dominant LTP versus OC-dominant LTP) were observed. In the sulfate-dominant LTP events, air masses directly arrived at Gosan without passing over the Korean Peninsula from the industrial area of China within 48 hr. During these events, the aerosol optical depth (AOD) increased to 1.63. Ionic balance data suggest that the long-range transported aerosols are acidic. In the OC-dominant LTP event, a higher residence time of air masses in Korea was observed (the air masses departing from the mainland of China arrived at the sampling site after passing Korea within 60–80 hr).Implications: In Northeast Asia, various natural and anthropogenic sources contribute to the complex chemical components and affect local/regional air quality and climate change. Chemical characteristics of long-range-transported (LTP) PM2.5 were investigated during spring and fall of 2008, 2009, 2011, and 2012. Based on air mass types, sulfate-dominant LTP and OC-dominant LTP were observed. A long-term variation and chemical characteristics of PM2.5 along with air mass and satellite data are required to better understand long-range-transported aerosols.

A study on the reconstitution of daily PM10 and PM2.5 levels in Paris with a multivariate linear regression model

The amount of time air spends over a region is linearly related to the region's contribution in PM. The residence time of air masses over emission sources was the main criterion for the division in 15 regions-origins. Daily PM concentrations in Paris (France), were reconstituted by multiplying the air mass residence time for each-one of the 15 regions by a regression coefficient (Bk) expressing the ability of each region to enrich the daily PM concentrations. The comparison between observed and predicted values gave satisfactory results. Local regions contributed cumulatively more than 50% of PM2.5 and PM10 in an average daily basis, whereas the residing areas of air parcels were particularly located around the city. Due to the scarceness of eastern circulation, continental airflows were associated with few episodes of extreme aerosol contributions, whereas peak air mass residence time values were isolated above Germany.

Indicators reflecting local and transboundary sources of PM2.5 and PMCOARSE in Rome – Impacts in air quality

The keystone of this paper was to calculate and interpret indicators reflecting sources and air quality impacts of PM2.5 and PMCOARSE (PM10–PM2.5) in Rome (Italy), focusing on potential exogenous influences. A backward atmospheric trajectory cluster analysis was implemented. The likelihood of daily PM10 exceedances was studied in conjunction with atmospheric patterns, whereas a Potential Source Contribution Function (PSCF) based on air mass residence time was deployed on a grid of a 0.5° × 0.5° resolution. Higher PM2.5 concentrations were associated with short/medium range airflows originated from Balkan Peninsula, whereas potential PMCOARSE sources were localized across the Mediterranean and coastal North Africa, due to dust and sea spray transportation. According to the outcome of a daily Pollution Index (PI), a slightly increased degradation of air quality is induced due to the additional quantity of exogenous PM but nevertheless, average levels of PI in all trajectory clusters belong in the low pollution category. Gaseous and particulate pollutants were also elaborated by a Principal Component Analysis (PCA), which produced 4 components: [Traffic], [photochemical], [residential] and [Secondary Coarse Aerosol], reflecting local sources of air pollution. PM2.5 levels were strongly associated with traffic, whereas PMCOARSE were produced autonomously by secondary sources.

Decomposing the profile of PM in two low polluted German cities – Mapping of air mass residence time, focusing on potential long range transport impacts

This paper aims to decompose the profile of particulates in Karlsruhe and Potsdam (Germany), focusing on the localization of PM potential transboundary sources. An air mass cluster analysis was implemented, followed by a study of air mass residence time on a grid of a 0.5° × 0.5° resolution. Particulate/gaseous daily air pollution and meteorological data were used to indicate PM local sources. Four Principal Component Analysis (PCA) components were produced: traffic, photochemical, industrial/domestic and particulate. PM2.5/PM10 ratio seasonal trends, indicated production of PMCOARSE (PM10–PM2.5) from secondary sources in Potsdam during warm period (WP). The residing areas of incoming slow moving air masses are potential transboundary PM sources. For Karlsruhe those areas were mainly around the city. An air mass residence time secondary peak was observed over Stuttgart. For Potsdam, areas with increased dwelling time of the arriving air parcels were detected particularly above E/SE Germany.

First simultaneous measurements of ozone, CO, and NOy at a high‐altitude regional representative site in the central Himalayas

AbstractSimultaneous in situ measurements of ozone, CO, and NOy have been made for the first time at a high altitude site Nainital (29.37°N, 79.45°E, 1958 m above mean sea level) in the central Himalayas during 2009–2011. CO and NOy levels discern slight enhancements during the daytime, unlike in ozone. The diurnal patterns are attributed mainly to the dynamical processes including vertical winds and the boundary layer evolution. Springtime higher levels of ozone (57.5 ± 12.6 ppbv), CO (215.2 ± 147 ppbv), and NOy (1918 ± 1769.3 parts per trillion by volume (pptv)) have been attributed mainly to regional pollution supplemented with northern Indian biomass burning. However, lower levels of ozone (34.4 ± 18.9 ppbv), CO (146.6 ± 71 ppbv), and NOy (1128.6 ± 1035 pptv) during summer monsoon are shown to be associated with the arrival of air mass originated from marine regions. Downward transport from higher altitudes is estimated to enhance surface ozone levels over Nainital by 6.1–18.8 ppbv. The classification based on air mass residence time, altitude variations along trajectory, and boundary layer shows higher levels of ozone (57 ± 14 ppbv), CO (206 ± 125 ppbv), and NOy (1856 ± 1596 pptv) in the continental air masses when compared with their respective values (28 ± 13 ppbv, 142 ± 47 ppbv, and 226 ± 165 pptv) in the regional background air masses. In general, positive interspecies correlations are observed which suggest the transport of air mass from common source regions (except during winter). Ozone‐CO and ozone‐NOy slope values are found to be lower in comparison to those at other global sites, which clearly indicates incomplete in situ photochemistry and greater role of transport processes in this region. The higher CO/NOy value also confirms minimal influence of fresh emissions at the site. Enhancements in ozone, CO, and NOy during high fire activity period are estimated to be 4–18%, 15–76%, and 35–51%, respectively. Despite higher CO and NOy concentrations at Nainital, ozone levels are nearly similar to those at other global high‐altitude sites.

Assimilation of IASI partial tropospheric columns with an Ensemble Kalman Filter over Europe

Abstract. Partial lower tropospheric ozone columns provided by the IASI (Infrared Atmospheric Sounding Interferometer) instrument have been assimilated into a chemistry-transport model at continental scale (CHIMERE) using an Ensemble Square Root Kalman Filter (EnSRF). Analyses are made for the month of July 2007 over the European domain. Launched in 2006, aboard the MetOp-A satellite, IASI shows high sensitivity for ozone in the free troposphere and low sensitivity at the ground; therefore it is important to evaluate if assimilation of these observations can improve free tropospheric ozone, and possibly surface ozone. The analyses are validated against independent ozone observations from sondes, MOZAIC1 aircraft and ground based stations (AIRBASE – the European Air quality dataBase) and compared with respect to the free run of CHIMERE. These comparisons show a decrease in error of 6 parts-per-billion (ppb) in the free troposphere over the Frankfurt area, and also a reduction of the root mean square error (respectively bias) at the surface of 19% (33%) for more than 90% of existing ground stations. This provides evidence of the potential of data assimilation of tropospheric IASI columns to better describe the tropospheric ozone distribution, including surface ozone, despite the lower sensitivity. The changes in concentration resulting from the observational constraints were quantified and several geophysical explanations for the findings of this study were drawn. The corrections were most pronounced over Italy and the Mediterranean region, we noted an average reduction of 8–9 ppb in the free troposphere with respect to the free run, and still a reduction of 5.5 ppb at ground, likely due to a longer residence time of air masses in this part associated to the general circulation pattern (i.e. dominant western circulation) and to persistent anticyclonic conditions over the Mediterranean basin. This is an important geophysical result, since the ozone burden is large over this area, with impact on the radiative balance and air quality. 1 Measurements of OZone, water vapour, carbon monoxide and nitrogen oxides by in-service AIrbus airCraft (http://mozaic.aero.obs-mip.fr/web/).

African dust source regions for observed dust outbreaks over the Subtropical Eastern North Atlantic region, above 25°N

High mineral dust-laden air mass potential source regions affecting the Marine Boundary Layer (MBL) of the Subtropical Eastern North Atlantic Region above 25°N (SENAR), directly or by means of gravitational settlement, were objectively identified. We introduced a new hybrid Lagrangian-Eulerian receptor model, in which air mass residence time probability maps in the geographical domain latitude = [5°N, 60°N], longitude = [70°W, 30°E] were combined with TOMS-AI data (TAPI Index), and with simulated Total Suspended Particles (TSP) with the BSC/DREAM model (SDPI Index). Both approaches show a good agreement. For dust gravitational settlement episodes within the MBL, the dust sources are located in southernmost latitudes compared to those associated with lower air mass transport. A seasonal variability in potential dust sources is found with both approaches, TAPI and SDPI. In winter, most dust sources are located within the Sahara in an area bounded by latitude = [18°N, 35°N], longitude = [15°W, 15°E]. In summer, a high dust-laden air mass reservoir above the Atlantic Ocean has been found during episodes for low altitudes, and dust source regions in the Sahara have been identified for middle and upper altitudes. The Bodelé depression was found to have a minor impact on dust outbreaks affecting the SENAR.

Influence of regional pollution and long range transport over western India: Analysis of ozonesonde data

Abstract Four years (April 2003 – July 2007) of ozonesonde observations over Ahmedabad have been studied for the first time using ten days backward trajectories in the boundary layer (lower 2 km) and lower troposphere (2.5–4 km). Ozone data are classified according to the residence times of air-masses over the North-Western India (NWI), marine and Northern Africa/Southern Europe (NASE) regions. Ozone increases linearly with increasing residence days over the NWI region for about six days with maximum increase rate (boundary layer ∼4.5 ± 1.1 ppbv/day, lower troposphere ∼3.4 ± 0.8 ppbv/day) during spring and minimum during winter (boundary layer ∼0.7 ± 0.8 ppbv/day, lower troposphere ∼0.8 ± 0.7 ppbv/day). The analysis of surface ozone over Ahmedabad confirms that ozone increase with residence days is largely due to photochemical build up. The estimated background ozone corresponding to zeroth residence day is found to be significantly lower during summer-monsoon (∼26.3 ± 3.3 ppbv) than winter (∼47.7 ± 3.2 ppbv) within the boundary layer. The air masses mainly influenced by NWI region, marine and NASE regions are termed as regionally polluted, marine and long range transport (LRT) respectively. The regionally polluted ozone is found to be higher than the average ozone during spring and summer-monsoon by 22–41% within the boundary layer and by 9–12% in the lower troposphere. The marine air shows lower ozone by 38% and 10% during spring and summer seasons respectively in the boundary layer. LRT plays a significant role in the lower troposphere during spring and summer seasons with an ozone enhancement of 9% and 27% respectively. The present work suggests that regional pollution and long range transport have significant influence on the seasonal distribution of ozone in the lower troposphere whereas the background ozone levels in summer-monsoon are mainly influenced by marine air mass over this region.

Chemical size distributions of boundary layer aerosol over the Atlantic Ocean and at an Antarctic site

Chemical size distributions of aerosols were measured using a 12‐stage low‐pressure impactor over the Atlantic Ocean in November–December 1999 and at an Antarctic site, Aboa, in January 2000. In the polluted latitudes north of the equator, particles were neutral in all sizes but accumulation mode was acidic in the clean areas. Chloride depletion was analyzed in detail. In most areas, chloride depletion could be explained by replacement by sulfate, nitrate, and methane sulfonate. In Antarctica the chloride losses increased in all size ranges and the contribution of each anion to the chloride depletion varied with increasing air mass residence time over continental Antarctica. The modal structure of the size distributions of ionic compounds was analyzed. The modes derived from chemical mass size distributions were compared with modes obtained from number size distributions. The modes of non‐sea‐salt sulfate and MSA were very similar suggesting that these particles were internally mixed. The nitrate mass modes were closer to the sea salt surface modes than the sea salt mass modes, suggesting that nitrate was on the surface of sea salt particles.