The vertical profile of atmospheric heating rate of black carbon aerosols at Kanpur in northern India

Altitude profiles of the mass concentrations of aerosol black carbon (BC) and composite aerosols were obtained from the collocated measurements of these quantities onboard an aircraft, over the urban area of Kanpur, in the Ganga basin of northern India during summer, for the first time in India. The enhancement in the mean BC concentration was observed at ∼1200 m in the summer, but the vertical gradient of BC concentration is less than the standard deviation at that altitude. The difference in the BC altitude profile and columnar concentration in the winter and summer is attributed to the enhanced turbulent mixing within the boundary layer in summer. This effect is more conspicuous with BC than the composite aerosols, resulting in an increase in the BC mass fraction (F_BC) at higher levels in summer. This high BC fraction results in an increase in the lower atmospheric heating rate in both the forenoon, FN and afternoon, AN, but with contrasting altitude profile. The FN profile shows fluctuating trend with highest value (2.1 K day⁻¹) at 300 m and a secondary peak at 1200 m altitudes, whereas the AN profile shows increasing trend with highest value (1.82 K day⁻¹) at 1200 m altitude.     

Characterisation of fresh particulate vehicular exhausts near a Paris high flow road

Simultaneous continuous measurements of PM_2.5, PM₁₀, black carbon mass (BCae), Black smoke (BS) and particle number density (N) were conducted in the close vicinity of a high traffic road around Paris during a three-month period beginning in August 1997. In parallel some aerosol collection was performed on filters in order to assess the black carbon (BC), organic carbon (OC) and water soluble organic fractions (WSOC) of the freshly emitted traffic aerosols. The high hourly concentrations of PM_2.5 (39±20 μg m⁻³), BCae (14±7 μg m⁻³), and N (220,000±115,000 cm⁻³), were found to be well correlated with each other. On average PM_2.5 represented 66±13% of PM₁₀ and appears to be composed primarily of BC (43±20%). On the contrary no correlation was found between PM_2.5 and the coarse (PM₁₀–PM_2.5) mass fractions which was attributed to resuspension processes by vehicles. Black carbon mass concentrations obtained from both filter analyses (BC) and Aethalometre data (BCae) show a good agreement suggesting that the Aethalometre calibration based on a black carbon specific attenuation coefficient (σ) of 19 m² g⁻¹ is well adapted to nearby roadside measurements. Daily BC (used as a surrogate for fine particles) concentrations and wind speed were found to be anti-correlated. Average daily variations of BC could be related to traffic intensity and regime as well as to the boundary layer height. As expected for freshly emitted traffic aerosols, filter analyses indicated a high BC/TC ratio (29±5%) and a low mean WSOC/OC ratio (12.5±5%) for the bulk aerosol. For these two ratios no day/night differences were observed, the sampling station being probably too close to traffic to evidence photochemical modification of the aerosol phase. Finally, a linear relationship was found between BC and BS hourly concentrations (BC=0.10×BS+1.18; r²=0.93) which offers interesting perspectives to retrieve BC concentrations from existing BS archives.     

On the contribution of black carbon to the composite aerosol radiative forcing over an urban environment

This paper discusses the extent of Black Carbon (BC) radiative forcing in the total aerosol atmospheric radiative forcing over Pune, an urban site in India. Collocated measurements of aerosol optical properties, chemical composition and BC were carried out for a period of six months (during October 2004 to May 2005) over the site. Observed aerosol chemical composition in terms of water soluble, insoluble and BC components were used in Optical Properties of Aerosols and Clouds (OPAC) to derive aerosol optical properties of composite aerosols. The BC fraction alone was used in OPAC to derive optical properties of BC aerosols. The aerosol optical properties for composite and BC aerosols were separately used in SBDART model to derive direct aerosol radiative forcing due to composite and BC aerosols. The atmospheric radiative forcing for composite aerosols were found to be +35.5, +32.9 and +47.6 Wm^?2 during post-monsoon, winter and pre-monsoon seasons, respectively. The average BC mass fraction found to be 4.83, 6.33 and 4 μg m^?3 during the above seasons contributing around 2.2 to 5.8% to the total aerosol load. The atmospheric radiative forcing estimated due to BC aerosols was +18.8, +23.4 and +17.2 Wm^?2, respectively during the above seasons. The study suggests that even though BC contributes only 2.2–6% to the total aerosol load; it is contributing an average of around 55% to the total lower atmospheric aerosol forcing due to strong radiative absorption, and thus enhancing greenhouse warming.     

Source apportionment of ambient PM2.5 at five spanish centres of the european community respiratory health survey (ECRHS II)

Fine particulate matter (PM_2.5) was sampled at 5 Spanish locations during the European Community Respiratory Health Survey II (ECRHS II). In an attempt to identify and quantify PM_2.5 sources, source contribution analysis by principal component analysis (PCA) was performed on five datasets containing elemental composition of PM_2.5 analysed by ED-XRF. A total of 4–5 factors were identified at each site, three of them being common to all sites (interpreted as traffic, mineral and secondary aerosols) whereas industrial sources were site-specific. Sea-salt was identified as independent source at all coastal locations except for Barcelona (where it was clustered with secondary aerosols). Despite their typically dominant coarse grain-size distribution, mineral and marine aerosols were clearly observed in PM_2.5. Multi-linear regression analysis (MLRA) was applied to the data, showing that traffic was the main source of PM_2.5 at the five sites (39–53% of PM_2.5, 5.1–12.0 μg m⁻³), while regional-scale secondary aerosols accounted for 14–34% of PM_2.5 (2.6–4.5 μg m⁻³), mineral matter for 13–31% (2.4–4.6 μg m⁻³) and sea-salt made up 3–7% of the PM_2.5 mass (0.4–1.3 μg m⁻³). Consequently, despite regional and climatic variability throughout Spain, the same four main PM_2.5 emission sources were identified at all the study sites and the differences between the relative contributions of each of these sources varied at most 20%. This would corroborate PM_2.5 as a useful parameter for health studies and environmental policy-making, owing to the fact that it is not as subject to the influence of micro-sitting as other parameters such as PM₁₀. African dust inputs were observed in the mineral source, adding on average 4–11 μg m⁻³ to the PM_2.5 daily mean during dust outbreaks. On average, levels of Al, Si, Ti and Fe during African episodes were higher by a factor of 2–8 with respect to non-African days, whereas levels of local pollutants (absorption coefficient, S, Pb, Cl) showed smaller variations (factor of 0.5–2).     

Development of an improved optical transmission technique for black carbon (BC) analysis

A new optical transmission technique for black carbon (BC) analysis was developed to minimize interferences due to scattering effects in filter samples. A standard thermal analysis method (VDI, 1999) is used to link light attenuation by the filter samples to elemental carbon (EC) concentration. Scattering effects are minimized by immersion of the filters in oil of a similar refractive index, as is often done for microscopy purposes. Light attenuation was measured using both a white light source and a red LED of 650 nm. The usual increase in overestimation of BC concentrations with decreasing BC amount in filter samples was found considerably reduced. Some effects of BC properties (e.g. fractal dimension, microstructure and size distribution) on the specific attenuation coefficient B_ATN, however, are still present for the treated samples. B_ATN was found close to 1 m² g⁻¹ for dry-dispersed industrial BC and 7 m² g⁻¹ for nebulized BC. Good agreement was found between the oil immersion, integrating sphere and a polar photometer technique and Mie calculations. The average specific attenuation coefficient of ambient samples in oil varied between 7 and 11 m² g⁻¹ for white light and 6 and 9 m² g⁻¹ for red light (LED). B_ATN was found to have much less site variation for the treated than for the untreated samples. The oil immersion technique improved also the correlation with thermally analyzed EC. This new immersion technique therefore presents a considerable improvement over conventional optical transmission techniques and may therefore serve as a simple, fast and cost-effective alternative to thermal methods.     

Present and potential future contributions of sulfate,black and organic carbon aerosols from China to global air quality,premature mortality and radiative forcing

Aerosols are harmful to human health and have both direct and indirect effects on climate. China is a major contributor to global emissions of sulfur dioxide (SO₂), a sulfate (SO₄^2?) precursor, organic carbon (OC), and black carbon (BC) aerosols. Although increasingly examined, the effect of present and potential future levels of these emissions on global premature mortality and climate change has not been well quantified. Through both direct radiative effects and indirect effects on clouds, SO₄^2? and OC exert negative radiative forcing (cooling) while BC exerts positive forcing (warming). We analyze the effect of China's emissions of SO₂, SO₄^2?, OC and BC in 2000 and for three emission scenarios in 2030 on global surface aerosol concentrations, premature mortality, and radiative forcing (RF). Using global models of chemical transport (MOZART-2) and radiative transfer (GFDL RTM), and combining simulation results with gridded population data, mortality rates, and concentration–response relationships from the epidemiological literature, we estimate the contribution of Chinese aerosols to global annual premature mortality and to RF in 2000 and 2030. In 2000, we estimate these aerosols cause approximately 470 000 premature deaths in China and an additional 30 000 deaths globally. In 2030, aggressive emission controls lead to a 50% reduction in premature deaths from the 2000 level to 240 000 in China and 10 000 elsewhere, while under a high emissions scenario premature deaths increase 50% from the 2000 level to 720 000 in China and to 40 000 elsewhere. Because the negative RF from SO₄^2? and OC is larger than the positive forcing from BC, Chinese aerosols lead to global net direct RF of ?74 mW m^?2 in 2000 and between ?15 and ?97 mW m^?2 in 2030 depending on the emissions scenario. Our analysis indicates that increased effort to reduce greenhouse gases is essential to address climate change as China's anticipated reduction of aerosols will result in the loss of net negative radiative forcing.     

PM2.5 particles and size-segregated ionic species measured during fall season in three urban sites in Korea

Twelve hours integrated fine particles (PM_2.5) and 24-h average size-segregated particles were collected to investigate the chemical characteristics and to determine the size distribution of ionic species during October–December 1999 in three cities of different urban scale; Chongju, Kwangju, and Seoul, Korea. Concentrations of 5-min PM_2.5 black carbon (BC) and hourly criteria air pollutants (PM₁₀, CO, NO_x, SO₂, and O₃) were also measured using the Aethalometer and ambient air monitoring system, respectively.Highest PM_2.5 mass concentrations at Chongju, Kwangju, and Seoul sites were 63.0, 77.9, and 143.7 μg m⁻³, respectively. For the time period when highest PM_2.5 mass occurred, BC level out of PM_2.5 chemical species was highest at both Chongju and Kwangju, and highest NO₃⁻ (23.6 μg m⁻³) followed by BC (23.1 μg m⁻³) were observed at Seoul site, indicating that highest PM_2.5 pollution is closely associated with the traffic emissions. Strong relationships of Fe with BC and Zn at both Kwangju and Seoul sites support that the Fe and Zn measured there are originated partly from same source as BC, i.e. diesel traffics. However, it is suggested that the Fe measured at Chongju is most likely derived from dispersion of soil dust.The size distributions of SO₄²⁻, NO₃⁻, and NH₄⁺ ionic species indicated similar unimodal distributions at all sampling sites. However, different unimodal patterns in the accumulation mode size range with a peak in the smaller size (0.28–0.53 μm, condensation mode) in both Kwangju and Seoul, and in the relatively larger size (0.53–1.0 μm, droplet mode) in Chongju, were found. The potassium ion under the study sites dominates in the fine mode, and its size distribution showed unimodal character with a maximum in the size range 0.56–1.0 μm.     

Carbon content of atmospheric aerosols in a residential area during the wood combustion season in Sweden

Carbonaceous aerosol particles were observed in a residential area with wood combustion during wintertime in Northern Sweden. Filter samples were analyzed for elemental carbon (EC) and organic carbon (OC) content by using a thermo-optical transmittance method. The light-absorbing carbon (LAC) content was determined by employing a commercial Aethalometer and a custom-built particle soot absorption photometer. Filter samples were used to convert the optical signals to LAC mass concentrations. Additional total PM₁₀ mass concentrations and meteorological parameters were measured. The mean and standard deviation mass concentrations were 4.4±3.6 μg m⁻³ for OC, and 1.4±1.2 μg m⁻³ for EC. On average, EC accounted for 10.7% of the total PM₁₀ and the contribution of OC to the total PM₁₀ was 35.4%. Aethalometer and custom-built PSAP measurements were highly correlated (R²=0.92). The hourly mean value of LAC mass concentration was 1.76 μg m⁻³ (median 0.88 μg m⁻³) for the winter 2005–2006. This study shows that the custom-built PSAP is a reliable alternative for the commercial Aethalometer with the advantage of being a low-cost instrument.     

On radiative effects of black carbon and sulphate aerosols

Most aerosol particles, such as sulphate and sea-salt particles, mainly scatter solar radiation, whilst soot (in the form of elemental carbon or “black” carbon, BC) in addition leads to considerable absorption. This scattering and absorption by the aerosol particles constitute the so-called direct aerosol effect. In this paper, we present results from a study of possible direct effects of tropospheric BC and sulphate aerosols, with an emphasis on BC aerosols, along a line from North Africa through Europe into the Arctic. Radiative budgets in a cloud-free atmosphere are estimated. Based on model-calculated distributions of BC and sulphate (provided by Seland and Iversen, 1998) and assumed size distributions of the background aerosol, new size distributions are obtained by adding natural, biomass burning and fossil fuel contributions to the background aerosol. Added nucleation mode particles are assumed externally mixed, whereas added accumulation mode BC and sulphate is internally mixed with the background according to condensational growth and Brownian coagulation theory. Humidity effects are taken into account by use of the Köhler equation. Mie calculations provide the resulting optical parameters, and the forcing is finally estimated by use of a radiative transfer model. A reference run and a series of eleven test-runs are performed to investigate the sensitivity of various assumptions on the contribution to upward TOA irradiance from BC and non-sea-salt sulphate. The tests suggest a high sensitivity to presence of BC and to particle swelling due to humidity. The sensitivity to assumed distribution of BC on particle size is more moderate. The same is true for the vertical resolution and the number concentration of the background aerosol. The effect of mixing organic carbon (OC) internally with biomass burning BC nucleation mode particles is characterized as moderate. The role of OC is, however, still uncertain. The same holds true for the optical thickness of the background atmosphere, for which we found a high sensitivity in this study. Other assumptions that were investigated had only small effects on the forcing. For the reference run we find a minimum in the aerosol forcing of approximately −5 W m^-2 near the most polluted areas in Europe, and a maximum of approximately 2 W m^-2 over North Africa. A warming effect is also found for the Arctic region, with forcing values up to 0.4 W m^-2.     

Carbonaceous and inorganic composition in long-range transported aerosols over northern Japan: Implication for aging of water-soluble organic fraction

To better understand the influence of sources and atmospheric processing on aerosol chemical composition, we collected atmospheric particles in Sapporo, northern Japan during spring and early summer 2005 under the air mass transport conditions from Siberia, China and surrounding seas. The aerosols were analyzed for inorganic ions, organic carbon (OC), elemental carbon (EC), water-soluble organic carbon (WSOC), and the major water-soluble organic compound classes (i.e., dicarboxylic acids and sugars). SO₄^2? is the most abundant inorganic constituent (average 44% of the identified inorganic ion mass) followed by NH₄⁺ (21%) and NO₃^? (13%). Concentrations of OC, EC, and WSOC ranged from 2.0–16, 0.24–2.9, and 0.80–7.9 μg m^?3 with a mean of 7.4, 1.0, and 3.1 μg m^?3, respectively. High OC/EC ratios (range: 3.6–19, mean: 8.7) were obtained, however WSOC/OC ratios (0.23–0.69, 0.44) do not show any significant diurnal changes. These results suggest that the Sapporo aerosols were already aged, but were not seriously affected by local photochemical processes. Identified water-soluble organic compounds (diacids + sugars) account for <10% of WSOC. Based on some marker species and air mass back trajectory analyses, and using stable carbon isotopic compositions of shorter-chain diacids (i.e., C₂–C₄) as photochemical aging factor of organic aerosols, the present study suggests that a fraction of WSOC in OC is most likely influenced by aerosol aging, although the OC loading in aerosols may be more influenced by their sources and source regions.     

Inventory of aerosol and sulphur dioxide emissions from India. Part II—biomass combustion

A spatially resolved biomass burning data set, and related emissions of sulphur dioxide and aerosol chemical constituents was constructed for India, for 1996–1997 and extrapolated to the INDOEX period (1998–1999). Sources include biofuels (wood, crop waste and dung-cake) and forest fires (accidental, shifting cultivation and controlled burning). Particulate matter (PM) emission factors were compiled from studies of Indian cooking stoves and from literature for open burning. Black carbon (BC) and organic matter (OM) emissions were estimated from these, accounting for combustion temperatures in cooking stoves. Sulphur dioxide emission factors were based on fuel sulphur content and reported literature measurements. Biofuels accounted 93% of total biomass consumption (577 MT yr⁻¹), with forest fires contributing only 7%. The national average biofuel mix was 56 : 21 : 23% of fuelwood, crop waste and dung-cake, respectively. Compared to fossil fuels, biomass combustion was a minor source of SO₂ (7% of total), with higher emissions from dung-cake because of its higher sulphur content. PM_2.5 emissions of 2.04 Tg yr⁻¹ with an “inorganic fraction” of 0.86 Tg yr⁻¹ were estimated. Biomass combustion was the major source of carbonaceous aerosols, accounting 0.25 Tg yr⁻¹ of BC (72% of total) and 0.94 Tg yr⁻¹ of OM (76% of total). Among biomass, fuelwood and crop waste were primary contributors to BC emissions, while dung-cake and forest fires were primary contributors to OM emissions. Northern and the east-coast India had high densities of biomass consumption and related emissions. Measurements of emission factors of SO₂, size resolved aerosols and their chemical constituents for Indian cooking stoves are needed to refine the present estimates.     

Aerosol mass-size distributions at a tropical coastal environment: response to mesoscale and synoptic processes

Regular measurements of total mass concentration and mass-size distribution of near-surface aerosols, made using a ten-channel Quartz Crystal Microbalance (qcm) Impactor for the period October 1998–December 1999 at the tropical coastal station Trivandrum (8.5°N, 77°E), are used to study the response of aerosol characteristics to regional mesoscale and synoptic processes. Results reveal that aerosol mass concentrations are generally higher under land breeze conditions. The sea breeze generally has a cleansing effect, depleting the aerosol loading. The continental air (LB regime) is richer in accumulation mode (submicron) aerosols than the marine air. On a synoptic scale, aerosol mass concentration in the submicron mode decreased from an average high value of ∼86 μg m⁻³ during the dry months (January–March) to ∼11 μg m⁻³ during the monsoon season (June–September). On the contrary mass concentration in the supermicron mode increased from a low value of ∼15 μg m⁻³ during the dry months to reach a comparatively high value of ∼35 μg m⁻³ during April, May. Correspondingly, the effective radius (R_eff) increased from a low value of 0.15–0.17 μm to ∼0.3 μm indicating a seasonal change in the size distribution. The mass-size distribution shows mainly three modes, a fine mode (∼0.1 μm); a large mode (∼0.5 μm) and a coarse mode (∼3 μm). The fine mode dominates in winter. In summer the large mode becomes more conspicuous and the coarse mode builds up. The fine mode is highly reduced in monsoon and the large and coarse modes continue to remain high (replenished) so that their relative dominance increases. The size distribution tends to revert to the winter pattern in the post-monsoon season. Accumulation (submicron) aerosols account for ∼98% of the total surface area and ∼70% of the total volume of aerosols during winter. During monsoon, even though they still account for ∼90% of the area, their contribution to the volume is reduced to ∼50%; the coarse aerosols account for the rest.     

Multi-year hourly PM2.5 carbon measurements in New York: Diurnal,day of week and seasonal patterns

Multi-year hourly measurements of PM_2.5 elemental carbon (EC) and organic carbon (OC) from a site in the South Bronx, New York were used to examine diurnal, day of week and seasonal patterns. The hourly carbon measurements also provided temporally resolved information on sporadic EC spikes observed predominantly in winter. Furthermore, hourly EC and OC data were used to provide information on secondary organic aerosol formation. Average monthly EC concentrations ranged from 0.5 to 1.4 μg m^?3 with peak hourly values of several μg m^?3 typically observed from November to March. Mean EC concentrations were lower on weekends (approximately 27% lower on Saturday and 38% lower on Sunday) than on weekdays (Monday to Friday). The weekday/weekend difference was more pronounced during summer months and less noticeable during winter. Throughout the year EC exhibited a similar diurnal pattern to NO_x showing a pronounced peak during the morning commute period (7–10 AM EST). These patterns suggest that EC was impacted by local mobile emissions and in addition by emissions from space heating sources during winter months. Although EC was highly correlated with black carbon (BC) there was a pronounced seasonal BC/EC gradient with summer BC concentrations approximately a factor of 2 higher than EC. Average monthly OC concentrations ranged from 1.0 to 4.1 μg m^?3 with maximum hourly concentrations of 7–11 μg m^?3 predominantly in summer or winter months. OC concentrations generally correlated with PM_2.5 total mass and aerosol sulfate and with NO_x during winter months. OC showed no particular day of week pattern. The OC diurnal pattern was typically different than EC except in winter when OC tracked EC and NO_x indicating local primary emissions contributed significantly to OC during winter at the urban location. On average secondary organic aerosol was estimated to account for 40–50% of OC during winter and up to 63–73% during summer months.     

Physical characterization of aerosol particles during the Chinese New Year’s firework events

Measurements for particles 10 nm to 10 μm were taken using a Wide-range Particle Spectrometer during the Chinese New Year (CNY) celebrations in 2009 in Shanghai, China. These celebrations provided an opportunity to study the number concentration and size distribution of particles in an especial atmospheric pollution situation due to firework displays. The firework activities had a clear contribution to the number concentration of small accumulation mode particles (100–500 nm) and PM₁ mass concentration, with a maximum total number concentration of 3.8 × 10⁴ cm^?3. A clear shift of particles from nucleation and Aitken mode to small accumulation mode was observed at the peak of the CNY firework event, which can be explained by reduced atmospheric lifetimes of smaller particles via the concept of the coagulation sink. High particle density (2.7 g cm^?3) was identified as being particularly characteristic of the firework aerosols. Recalculated fine particles PM₁ exhibited on average above 150 μg m^?3 for more than 12 hours, which was a health risk to susceptible individuals. Integral physical parameters of firework aerosols were calculated for understanding their physical properties and further model simulation.     

Black carbon aerosols in urban air in South Asia

We report data from a yearlong (2006–2007) study of black carbon concentrations ([BC]) measured at 5-min intervals with an Aethalometer in Karachi, Pakistan. Daily mean [BC] varied from about 1 to 15 μg m^?3. However, short-term spikes exceeding 40 μg m^?3 were common, occurring primarily during the morning and evening rush-hour periods. The [BC] values were highest during November through February, ～10 μg m^?3, and lowest during June through September, ～2 μg m^?3. Diurnal, seasonal, and day-of-the-week trends are discussed. It is demonstrated that these trends are strongly affected by meteorological patterns. A simple expression is applied to the concentration profiles to separate the effects of meteorological conditions and elucidate the underlying emissions patterns. Daily emissions varied from 14,000 to 22,000 kg of BC per day. When integrated over the year emissions for Karachi Proper were estimated at 6.7 kilometric tons per year and emissions for greater Karachi were 17.5 kilometric tons per year. Folding in the populations of each area yields BC emissions of 0.74 and 1.1 kg per person per year, respectively. Applying the model to previously collected data at Lahore, Pakistan yields emissions during November–January that are around a factor of two higher than those in Karachi, but because the BC measurements in Lahore covered only three months, no estimates of annual emissions were attempted. Given the large populations of these cities the local health impact from PM alone is expected to be severe but because of the high [BC] emissions the impact on the global climate may be equally significant.     

Chemical composition of aerosols during a major biomass burning episode over northern Europe in spring 2006: Experimental and modelling assessments

The long-range transported smokes emitted by biomass burning had a strong impact on the PM_2.5 mass concentrations in Helsinki over the 12 days period in April and May 2006. To characterize aerosols during this period, the real-time measurements were done for PM_2.5, PM_2.5–10, common ions and black carbon. Moreover, the 24-h PM₁ filter samples were analysed for organic and elemental carbon (OC and EC), water-soluble organic carbon (WSOC), ions and levoglucosan. The Finnish emergency and air quality modelling system SILAM was used for the forecast of the PM_2.5 concentration generated by biomass burning. According to the real-time PM_2.5 data, the investigated period was divided into four types of PM situations: episode 1 (EPI-1; 25–29 April), episode 2 (EPI-2; 1–5 May), episode 3 (EPI-3; 5–6 May) and a reference period (REF; 24 March–24 April). EPI-3 included a local warehouse fire and therefore it is discussed separately. The PM₁ mass concentrations of biomass burning tracers—levoglucosan, potassium and oxalate—increased during the two long-range transport episodes (EPI-1 and EPI-2). The most substantial difference between the episodes was exhibited by the sulphate concentration, which was 4.9 (±1.4) μg m⁻³ in EPI-2 but only 2.4 (±0.31) μg m⁻³ in EPI-1 being close to that of REF (1.8±0.54 μg m⁻³). The concentration of particulate organic matter in PM₁ was clearly higher during EPI-1 (11±3.3 μg m⁻³) and EPI-2 (9.7±4.0 μg m⁻³) than REF (1.3±0.45 μg m⁻³). The long-range transported smoke had only a minor impact on the WSOC-to-OC ratio. According to the model simulations, MODIS detected the fires that caused the first set of concentration peaks (EPI-1) and the local warehouse fire (EPI-3), but missed the second one (EPI-2) probably due to dense frontal clouds.     

Estimating the impact of Saharan dust on the year 2001 PM10 record of Rome,Italy

This paper evaluates the role of Saharan dust advection in the exceeding of the PM₁₀ thresholds in the city of Rome, Italy. To this purpose, a series of observations and model forecasts recorded in the year 2001 are analysed and discussed. Lidar profiles collected over 168 days of the year are employed to both assess the presence and magnitude of Saharan dust layers over the city and to evaluate the depth of the planetary boundary layer. Backtrajectories are used to verify the Saharan origin of the lidar-sounded air masses. Model predictions of the presence of Saharan dust over the area are employed to fill the time gaps between lidar observations. PM₁₀ and carbon monoxide records of both a city background (Villa Ada) and a heavy traffic station (Magna Grecia) are cross-analysed with the dust events record and meteorological data. The analysis shows that: (1) Saharan dust was advected over Rome on about 30% of the days of 2001; (2) mean contribution of Saharan dust transport events to daily PM₁₀ levels was of the order of 20 μg m⁻³; (3) at the urban background station of Villa Ada, the Saharan contribution caused the surpassing of the maximum number of days in excess of 50 μg m⁻³ fixed by the current legislation (35 per year). Conversely, at the heavy traffic station of Magna Grecia the Saharan contribution was not determinant at causing the observed large exceeding of that limit, as well as of the maximum yearly average of 40 μg m⁻³; (4) 25% of the Saharan advection days (of the order of 100/year at Rome) led to a PM₁₀ increase >30 μg m⁻³, 4% caused an increase >50 μg m⁻³, thus leading on their own to surpassing the 50 μg m⁻³ daily limit.     

Field validation of a semi-continuous method for aerosol black carbon (aethalometer) and temporal patterns of summertime hourly black carbon measurements in southwestern PA

Two methods for measuring aerosol elemental carbon (EC) are compared. Three-hour integrated carbon samples were collected on quartz filters during the summer of 1990 in Uniontown, PA, primarily during episodes of elevated particulate pollution levels. These samples were analyzed for EC and organic carbon (OC) using a thermo/optical reflectance (TOR) method. Aerosol black carbon (BC) was measured using an Aethalometer, a semi-continuous optical absorption method. The optical attenuation factor for ambient BC was supplied by the instrument manufacturer. Three-hour average concentrations were calculated from the semi-continuous BC measurements to temporally match the EC/OC integrated quartz filter samples. BC and EC concentrations are highly correlated over the study period (R²=0.925). The regression equation is BC (μg m^-3)=0.95 (±0.04) EC−0.2 (±0.4). The means of 3 h average measurements for EC and BC are 2.3 and 2.0 μg m^-3, respectively, average concentrations of EC and BC ranged from 0.6 to 9.4 and 0.5 to 9.0 μg m^-3 respectively. TOR OC and EC concentrations were not highly correlated (R²=0.22). The mean OC/EC ratio was 1.85.The 10-week Aethalometer hourly dataset was analyzed for daily and weekly temporal patterns. A strong diurnal BC pattern was observed, with peaks occurring between 7 a.m. and 9 a.m. local time. This is consistent with the increase in emissions from ground level combustion sources in the morning, coupled with poor dispersion before daytime vertical mixing is established. There was also some indication of a day-of-week effect on BC concentrations, attributed to activity of local ground level anthropogenic sources. Comparison of BC concentrations with co-located measurements of coefficient of haze in a separate field study in Philadelphia, PA, during the summer of 1992 showed good correlation between the two measurements (R²=0.82).     

An empirical model for predicting urban roadside nitrogen dioxide concentrations in the UK

An annual mean concentration of 40 μg m⁻³ has been proposed as a limit value within the European Union Air Quality Directives and as a provisional objective within the UK National Air Quality Strategy for 2010 and 2005, respectively. Emissions reduction measures resulting from current national and international policies are likely to deliver significant reductions in emissions of oxides of nitrogen from road traffic in the near future. It is likely that there will still be exceedances of this target value in 2005 and in 2009 if national measures are considered in isolation, particularly at the roadside. It is envisaged that this `policy gap’ will be addressed by implementing local air quality management to reduce concentrations in locations that are at risk of exceeding the objective. Maps of estimated annual mean NO₂ concentrations in both urban background and roadside locations are a valuable resource for the development of UK air quality policy and for the identification of locations at which local air quality management measures may be required. Maps of annual mean NO₂ concentrations at both background and roadside locations for 1998 have been calculated using modelling methods, which make use of four mathematically straightforward, empirically derived linear relationships. Maps of projected concentrations in 2005 and 2009 have also been calculated using an illustrative emissions scenario. For this emissions scenario, annual mean urban background NO₂ concentrations in 2005 are likely to be below 40 μg m⁻³, in all areas except for inner London, where current national and international policies are expected to lead to concentrations in the range 40–41 μg m⁻³. Reductions in NO_x emissions between 2005 and 2009 are expected to reduce background concentrations to the extent that our modelling results indicate that 40 μg m⁻³ is unlikely to be exceeded in background locations by 2009. Roadside NO₂ concentrations in urban areas in 2005 and 2009 are expected to be significantly higher than in background locations. 21% of urban major road links are expected to have roadside NO₂ greater than or equal to 40 μg m⁻³ in 2005 for our illustrative emissions scenario. The continuing downward trend in traffic emissions is likely to further reduce the number of links exceeding this value by 2009, with about 6% of urban major road links predicted to have concentrations higher than 40 μg m⁻³. The majority of these links are in the London area. The remaining links are generally confined to the most heavily trafficked roads in other big cities.     

Secondary organic aerosol formation from the oxidation of aromatic hydrocarbons in the presence of dry submicron ammonium sulfate aerosol

A laboratory study was conducted to examine formation of secondary organic aerosols. A smog chamber system was developed for studying gas–aerosol interactions in a dynamic flow reactor. These experiments were conducted to investigate the fate of gas and aerosol phase compounds generated from hydrocarbon–nitrogen oxide (HC/NO_x) mixtures irradiated in the presence of fine (<2.5 μm) particulate matter. The goal was to determine to what extent photochemical oxidation products of aromatic hydrocarbons contribute to secondary organic aerosol formation through uptake on pre-existing inorganic aerosols in the absence of liquid water films. Irradiations were conducted with toluene, p-xylene, and 1,3,5-trimethylbenzene in the presence of NO_x and ammonium sulfate aerosol, with propylene added to enhance the production of radicals in the system. The secondary organic aerosol yields were determined by dividing the mass concentration of organic fraction of the aerosol collected on quartz filters by the mass concentration of the aromatic hydrocarbon removed by reaction. The mass concentration of the organic fraction was obtained by multiplying the measured organic carbon concentration by 2.0, a correction factor that takes into account the presence of hydrogen, nitrogen, and oxygen atoms in the organic species. The mass concentrations of ammonium, nitrate, and sulfate concentrations as well as the total mass of the aerosols were measured. A reasonable mass balance was found for each of the aerosols. The largest secondary organic aerosol yield of 1.59±0.40% was found for toluene at an organic aerosol concentration of 8.2 μm⁻³, followed by 1.09±0.27% for p-xylene at 6.4 μg m⁻³, and 0.41±0.10% for 1,3,5-trimethylbenzene at 2.0 μg m⁻³. In general, these results agree with those reported by Odum et al. and appear to be consistent with the gas–aerosol partitioning theory developed by Pankow. The presence of organic in the aerosol did not affect significantly the hygroscopic properties of the aerosol.