Suburban Background Sites Research Articles

How important is biogenic isoprene in an urban environment? A study in London and Paris

[1] As the emissions of anthropogenic volatile organic compounds (VOCs) are reduced through regulatory measures and improved control technologies, biogenic VOCs could gain in importance in terms of reactivity, especially in urban areas. Here we investigate a 12 year record of non-methane hydrocarbons (NMHCs) in central London and the importance of biogenics (in the form of isoprene) for ozone formation through the contribution to OH reactivity. Significant reductions in NMHCs were observed from 1998 through 2009 at an urban traffic site (−13% per year) and suburban background site (−5% per year) in London. Total isoprene levels decreased similarly and the relative contribution of isoprene to the total NMHC OH reactivity did not change. Furthermore, a dataset for Paris showed strong similarities to the data from London, which would indicate that these results are not limited to London. Interestingly, a rural site to the east of London, Harwell, showed similar contributions of isoprene to the total NMHC reactivity, which may indicate the need for measurements of other biogenic species, such as monoterpenes, in some areas to reliably capture the importance of biogenics in the region. These results would indicate that the influence of biogenic isoprene in London, and likely other low isoprene emitter urban areas have a long way to go before the importance of biogenic VOCs equals or exceeds that of anthropogenic contributions.

Contribution of the road traffic to air pollution in the Prague city (busy speedway and suburban crossroads)

Two measurement campaigns near busy freeway and suburban crossroad (different traffic intensity) were carried out in Prague city. Both of the two traffic related campaigns were supported with simultaneous measurements at suburban background site to compare measured values with corresponding city background. Extensive set of aerosol instrumentation was used during both campaigns at both measurement sites. Two aerosol spectrometer sets (SMPS and APS) were used to monitor aerosol particle number size distribution. Two BLPI provided information about mass size distribution and chemical composition of collected size resolved aerosol samples. The crossroad campaign was also supported by two EC/OC field analysers providing information about elemental and organic carbon concentrations. Consequent chemical analysis of collected size resolved samples comprised of ion chromatography (water soluble ions), PIXE (elements) and RBS (carbon). Results obtained from spectrometers and BLPIs showed that the main contribution of traffic in ultrafine size range can be attributed to direct exhaust emissions, while the coarse fraction was dominated mainly by regional background aerosol with small traces of brake and tyre abrasion as well as the resuspension of the road dust. Chemical analysis demonstrated that most of the water soluble ions can be found in fine fraction of mass distribution and mostly comes from regional background and long range transport. Most of major elements were found in coarse fraction of mass size distribution and it can be attributed to three different sources: abrasion of different vehicle parts (Fe, Cu, Mn and Zn), resuspension of the road dust (Si, Al, Ca) and long range transport or regional background (Ca and K). Elemental carbon concentration (diesel engine emissions) was found to be proportional to traffic intensity.

Simulations of organic aerosol concentrations in Mexico City using the WRF-CHEM model during the MCMA-2006/MILAGRO campaign

Abstract. Organic aerosol concentrations are simulated using the WRF-CHEM model in Mexico City during the period from 24 to 29 March in association with the MILAGRO-2006 campaign. Two approaches are employed to predict the variation and spatial distribution of the organic aerosol concentrations: (1) a traditional 2-product secondary organic aerosol (SOA) model with non-volatile primary organic aerosols (POA); (2) a non-traditional SOA model including the volatility basis-set modeling method in which primary organic components are assumed to be semi-volatile and photochemically reactive and are distributed in logarithmically spaced volatility bins. The MCMA (Mexico City Metropolitan Area) 2006 official emission inventory is used in simulations and the POA emissions are modified and distributed by volatility based on dilution experiments for the non-traditional SOA model. The model results are compared to the Aerosol Mass Spectrometry (AMS) observations analyzed using the Positive Matrix Factorization (PMF) technique at an urban background site (T0) and a suburban background site (T1) in Mexico City. The traditional SOA model frequently underestimates the observed POA concentrations during rush hours and overestimates the observations in the rest of the time in the city. The model also substantially underestimates the observed SOA concentrations, particularly during daytime, and only produces 21% and 25% of the observed SOA mass in the suburban and urban area, respectively. The non-traditional SOA model performs well in simulating the POA variation, but still overestimates during daytime in the urban area. The SOA simulations are significantly improved in the non-traditional SOA model compared to the traditional SOA model and the SOA production is increased by more than 100% in the city. However, the underestimation during daytime is still salient in the urban area and the non-traditional model also fails to reproduce the high level of SOA concentrations in the suburban area. In the non-traditional SOA model, the aging process of primary organic components considerably decreases the OH levels in simulations and further impacts the SOA formation. If the aging process in the non-traditional model does not have feedback on the OH in the gas-phase chemistry, the SOA production is enhanced by more than 10% compared to the simulations with the OH feedback during daytime, and the gap between the simulations and observations in the urban area is around 3 μg m−3 or 20% on average during late morning and early afternoon, within the uncertainty from the AMS measurements and PMF analysis. In addition, glyoxal and methylglyoxal can contribute up to approximately 10% of the observed SOA mass in the urban area and 4% in the suburban area. Including the non-OH feedback and the contribution of glyoxal and methylglyoxal, the non-traditional SOA model can explain up to 83% of the observed SOA in the urban area, and the underestimation during late morning and early afternoon is reduced to 0.9 μg m−3 or 6% on average. Considering the uncertainties from measurements, emissions, meteorological conditions, aging of semi-volatile and intermediate volatile organic compounds, and contributions from background transport, the non-traditional SOA model is capable of closing the gap in SOA mass between measurements and models.

Atmospheric aerosols in suburb of Prague: The dynamics of particle size distributions

The paper summarizes the results of a 2-year-long continuous sampling by SMPS and APS spectrometers at the suburban background site in Prague, Suchdol. The campaign was aimed to study the particle number size distributions and their dynamic behavior. It was found that the average total particle number concentration was 7.3 × 10 3 particles/cm 3. The size distributions were often bimodal. The peaks occurring in the accumulation (> 100 nm) and Aitken size range (25–100 nm) were sometimes overlapping each other. When new particles were formed, the peak in the nucleation size range (< 25 nm) dominated. The situations, when the number concentrations of particles smaller than 25 nm in diameter were elevated, mostly indicated the formation of new particles belonging to the category “Banana event.” The kinetic parameters of these nucleation events were estimated; the average value of the formation rate was found to be J 10 = 2.6 cm −3 s −1 and the growth rate GR 10 = 5.4 nm h − 1 . The paper also compares features of all the different situations and events observed, including typical clean days, days dominated by traffic related aerosols (during rush hours) or days characterized by local pollution events. On clean days, the average background particle number concentration was 4 × 10 3 particles/cm 3. On days with anthropogenic pollution, higher than average particle number concentrations were recorded throughout the whole size range with the total average concentration 20 × 10 3 particles/cm 3.

Pm2.5 Size Distribution and Characterization by Carbon Isotope in Tuscany (italy)

This study is focused on the numerical distribution and isotopic description of PM2.5 developed within the PATOS II (Particolato Atmosferico TOScana) regional project about the characterization and source apportionment of atmospheric aerosol (PM2.5) in Tuscany. PM isotopic analysis can play an important role in the individuation of primary and secondary sources and also in the determination of the natural/biogenic or anthropogenic/combustion contribution to the measured concentration. In addition, the PM2.5 particle number concentrations and the relative contribution of ultrafine particles are interpreted to identify the emission sources, the main atmospheric processes and the factors related with the dispersion of atmospheric pollutants. The analytical results in term of δC parameter show a greater variability in the urban and suburban background sites than in the urban traffic site, where the δC parameter does not vary significantly: this could be strictly correlated with traffic emissions and independently from the total particles number. On the contrary, urban and suburban background sites are affected by the meteorology and atmospheric processes. For this reason we can observe a wider variability in the δC values due to the contribution of different emissions sources. Despite all, in urban background we can observe lower δC values related with high number of total particles; this effect could be related with a traffic emission transport, because the δC parameter is similar to the δC value of urban traffic sites.

A simplified approach to the indirect evaluation of the chemical composition of atmospheric aerosols from PM mass concentrations

Abstract The present work shows a straightforward procedure to indirectly estimate the chemical composition at a given site only from the determination of the PM concentrations, and the classification of the days according to the main meteorological scenarios. A previous study based on the mean chemical composition associated to the main meteorological scenarios is required. This experiment has been carried out with data from two monitoring sites in the North-Western Mediterranean, one regional and one suburban background. At both sites, one-year datasets on chemical PM10 composition were obtained. Based on these datasets, the mean PM10 compositions according to the most relevant meteorological situations were calculated for both locations. After that, the reconstruction of the chemical composition for all the days with available PM10 concentrations was completed. Subsequently, the estimated PM10 composition was compared with that determined experimentally. The comparison between the rebuilt and the experimental results was very satisfactory in the case of the regional background site, and relatively replaced in the other case. Furthermore, the validation of the method at the regional background site has been conducted from the reconstruction of a 4-year data base, and subsequent comparison with the experimental chemical composition. Our results show that it is possible to attain a good approach to the chemical composition at regional background sites, where local emission sources are negligible. Conversely, when the local sources rise in importance, i.e., at a suburban background site, the approach is suitable only for those components with a more regional origin and/or those from long range transport of air masses.

Identification and characterisation of local aerosol sources using high temporal resolution measurements

Aerosol and gaseous pollution measurements were carried out at an urban background site in the south of Italy located near an industrial complex. Collection of 24 h samples of PM10 and PM2.5 and successive chemical quantification of metals were performed. Data were compared with measurements taken at a suburban background site, located at 25 km distance. The comparison showed the presence of an industrial contribution with a well defined chemical emission profile, similar, in terms of metals content, to urban emissions. As this made difficult the quantitative characterisation of the contribution of the two sources to atmospheric PM, a statistical method based on the treatment of data arising from high temporal resolution measurements was developed. Data were taken with a micrometeorological station based on an integrating nephelometer (Mie pDR-1200) for optical detection of PM2.5 concentration, with successive evaluation of vertical turbulent fluxes using the eddy-correlation method. Results show that the contribution from the two sources (urban emissions and industrial releases) have a very different behaviour, with the industrial contribution being present at high wind velocity with short concentration peaks (average duration 4 min) associated to strong positive and negative vertical fluxes. The estimated contribution to PM2.5 is 2.3% over long-term averages. The urban emissions are mainly present at low wind velocity, with longer concentration peaks in the morning and late evening hours, generally associated to small positive vertical fluxes. The characterisation of the contribution was performed using deposition velocity V(d) that is on average -3.5 mm s(-1) and has a diurnal pattern, with negligible values during the night and a minimum value of around -9 mm s(-1) late in the afternoon. Results show a correlation between V(d), friction velocity and wind velocity that could be the basis for a parameterisation of V(d) to be used in dispersion codes.

Comparison of Water-Soluble Organic Components in Size-Segregated Particles between a Roadside and a Suburban site in Saitama, Japan

To clarify the characteristics of the water-soluble organic components in atmospheric aerosols, size-separated aerosol samples were simultaneously collected at a roadside site (R) and a suburban background site (S) in Saitama, Japan, during spring and summer 2007 and winter 2008. Chemical compositions, including water-soluble organic carbon (WSOC), organic carbon, inorganic ionic components, and individual water-soluble organic acids (saturated dicarboxylic acids, unsaturated dicarboxylic acids, ketocarboxylic acids, and dicarbonyls), were analyzed in size-separated samples. The seasonal variation of WSOC in Saitama aerosols was larger than the spatial difference between the two sites, with summer WSOC concentrations being 2.5-2.8 times those in the other seasons. Seasonal average concentrations of the detected organic acids in PM7.0 were 542 ng/m^3 (R) and 670 ng/m^3 (S). Strong correlations were observed between C2-C5 n-dicarboxylic acids and ambient oxidants. The concentration ratios of individual n-dicarboxylic acids (C2-C5) to elemental carbon were significantly higher in suburban samples than in roadside samples, indicating that the contribution of secondary formation to these acids was larger in suburban samples. During the warm seasons, the concentrations of sulfate, ammonium, WSOC, and individual acids in fine particles were very high, whereas nitrate, chloride, sodium, and calcium concentrations were higher in coarse particles. Comparisons between the two sites showed that secondary formation contributed more to the total amount of particulate water-soluble organic acids in Saitama aerosols than direct emissions from anthropogenic and natural sources. However, vehicle exhaust was also an important source of dicarboxylic acids in Saitama aerosols, especially in the near-roadside environment.

High and low volume sampling of particulate matter at sites with different traffic profiles in the Netherlands and Germany: Results from the HEPMEAP study

Within the EU project “Health Effects of Particles from Motor Engine Exhaust and Ambient Pollution” (HEPMEAP), ambient particulate matter (PM) was collected at sites, with varying traffic density and sources of PM emissions, in the Netherlands and Munich, Germany. In the Netherlands, measurements were conducted close to four schools which had participated 4 years earlier in a study on respiratory health of children attending schools near motorways. In Munich, measurements were conducted at a high traffic inner city and a suburban background (low traffic) site. Measurements were spaced over a period of approximately 1 year. Collection of PM was conducted using both high volume and low volume impaction methods. In addition to PM mass, PM-absorbance (‘soot’) and NO 2 were measured as indicators of fossil fuel combustion. PM 2.5 and PM 10 concentrations calculated from the high volume collections were highly correlated with PM 2.5 and PM 10 concentrations measured simultaneously by low volume samplers ( R 2 0.87–0.94). Both high and low volume measurements showed little difference in semi annual average PM mass concentrations between sites within each country, with PM concentrations at the highest exposed sites being only about 10–30% higher compared to the lowest exposed sites. Contrasts for PM-absorbance and NO 2 were significantly higher than for PM mass (70–90% in the Netherlands and 90–167% in Germany). This demonstrates a higher impact of traffic on these components compared to PM mass.

An overview of the PM 10 pollution problem, in the Metropolitan Area of Athens, Greece. Assessment of controlling factors and potential impact of long range transport

The present study analyzes PM 10 concentration data collected by the Greek air quality monitoring network at 8 sites over the Greater Athens Area, for the period of 2001–2004. The primary objectives were to assess the degree of compliance with the EU-legislated air quality standard for PM 10 and also provide an overall statistical examination of the factors controlling the seasonal and spatial variation of concentrations, over the wider urban agglomeration. Daily concentrations, averaged over the whole study period, ranged between 32.3 and 60.9 μg m −3. The four-year average concentration of PM 10 at five sites exceeded the annual limit value of 40 μg m −3, while most of the sites surpassed the allowed percentage of exceedances of the daily limit value (50 μg m −3), for each of the four years. The seasonal variation of PM 10 levels was not found to be uniform across the eight sites, with average cold-period concentrations being higher at four of them and warm period concentrations being significantly higher at three sites, which also displayed recurring annual variation of monthly concentrations. Concentration levels displayed moderate spatial heterogeneity. Nevertheless significant inter-site correlations were observed (ranging between 0.55 and 085). The determination of the spatial correlation levels relied mainly on site types rather than on inter-site distances. Monitoring sites were classified accordingly using cluster analysis in two groups presenting distinct spatiotemporal variation and affected by different particle formation processes. The group including urban sites was mainly affected by primary, combustion-related processes and especially vehicular traffic, as it was also deduced through the examination of the diurnal distribution of particulate levels and through factor analysis. On the contrary, suburban background sites seemed more affected by particle transport from more polluted neighboring areas and secondary particle formation through gaseous precursors, both processes aided from favoring meteorological conditions. The association of the PM 10 levels with backwards trajectories was also examined, in an attempt to account for the possible long range transport of particles in Athens. It was found that a notable part of area-wide episodic events could be attributed to trans-boundary transport of particles, with the origins of some severe dust outbreaks traced back to the Sahara desert and the Western Mediterranean.

PM sources in a highly industrialised area in the process of implementing PM abatement technology. Quantification and evolution

Principal component analysis (PCA) coupled with a multilinear regression analysis (MLRA) was applied to PM(10) speciation data series (2002-2005) from four sampling sites in a highly industrialised area (ceramic production) in the process of implementing emission abatement technology. Five common factors with similar chemical profiles were identified at all the sites: mineral, regional background (influenced by the industrial estate located on the coast: an oil refinery and a power plant), sea spray, industrial 1 (manufacture and use of glaze components, including frit fusion) and road traffic. The contribution of the regional background differs slightly from site to site. The mineral factor, attributed to the sum of several sources (mainly the ceramic industry, but also with minor contributions from soil resuspension and African dust outbreaks) contributes between 9 and 11 microg m(-3) at all the sites. Source industrial 1 entails an increase in PM(10) levels between 4 and 5 microg m(-3) at the urban sites and 2 microg m(-3) at the suburban background site. However, after 2004, this source contributed less than 2 microg m(-3) at most sites, whereas the remaining sources did not show an upward or downward trend along the study period. This gradual decrease in the contribution of source industrial 1 coincides with the implementation of PM abatement technology in the frit fusion kilns of the area. This relationship enables us to assess the efficiency of the implementation of environmental technologies in terms of their impact on air quality.

Spatial variation in nitrogen dioxide in three European areas

In order to estimate the spatial variation within well-defined study areas, nitrogen dioxide was measured with diffusion samplers (Palmes tube) in 40–42 sites each in Germany (Munich), the Netherlands and Sweden (Stockholm County). Each site was measured over four 2-week periods during 1 year (spring 1999 to summer 2000). In each country, one reference site was measured during all periods and the results were used to adjust for seasonal variability, to improve the estimates of the annual average. Comparisons between the chemiluminescence method (European reference method) and Palmes tube measurement indicated a good agreement in Germany (with a ratio of 1.0 for Palmes tube/chemiluminescence) but underestimation for Palmes tube measurement in the Netherlands and Sweden (0.8 for both countries). The r 2 values were between 0.86 and 0.90 for all three countries. The annual average values for NO 2 for different sampling sites were between 15.9 and 50.6 (mean 28.8 μg/m 3) in Germany, between 12.1 and 50.8 (mean 28.9 μg/m 3) in the Netherlands and between 6.1 and 44.7 (mean 18.5 μg/m 3) in Sweden. Comparing spatial variation between similar sites in the three countries, we did not find any significant differences between annual average levels for urban traffic sites. In Sweden, annual average levels in urban background and suburban backgrounds sites were about 8 μg/m 3 lower than comparable sites in Germany and the Netherlands. Comparing site types within each country only urban traffic sites and suburban background sites differed in Germany. In the Netherlands and Sweden, the urban traffic sites differed from all other sites and in Sweden also the urban background sites differed from the other background sites. The observed contribution from local traffic was similar in the Netherlands and Sweden (10 and 8 μg/m 3, corresponding to 26–27% of the NO 2 concentration found in the urban traffic sites). In Germany, the contribution from local traffic was only 3 μg/m 3, corresponding to 9% of the NO 2 concentration found in the urban traffic sites. The spatial variation was substantially larger for NO 2 than the variation for PM 2.5 and similar to PM 2.5 absorbance, measured in the same locations.