Primary Aerosol Emissions Research Articles

Better constraints on sources of carbonaceous aerosols using a combined <sup>14</sup>C – macro tracer analysis in a European rural background site

Abstract. The source contributions to carbonaceous PM2.5 aerosol were investigated at a European background site at the edge of the Po Valley, in Northern Italy, during the period January–December 2007. Carbonaceous aerosol was described as the sum of 8 source components: primary (1) and secondary (2) biomass burning organic carbon, biomass burning elemental carbon (3), primary (4) and secondary (5) fossil organic carbon, fossil fuel burning elemental carbon (6), primary (7) and secondary (8) biogenic organic carbon. The mass concentration of each component was quantified using a set of macro tracers (organic carbon OC, elemental carbon EC, and levoglucosan), micro tracers (arabitol and mannitol), and 14C measurements. This was the first time that 14C measurements covered a full annual cycle with daily resolution. This set of 6 tracers, together with assumed uncertainty ranges of the ratios of OC-to-EC, and the reference fraction of modern carbon in the 8 source categories, provides strong constraints to the source contributions to carbonaceous aerosol. The uncertainty of contributions was assessed with a Quasi-Monte Carlo (QMC) method accounting for the variability of OC and EC emission factors, the uncertainty of reference fractions of modern carbon, and the measurement uncertainty. During winter, biomass burning composed 64 % (±15 %) of the total carbon (TC) concentration, while in summer secondary biogenic OC accounted for 50 % (±16 %) of TC. The contribution of primary biogenic aerosol particles was negligible during the entire year. Moreover, aerosol associated with fossil sources represented 27 % (±16 %) and 41 % (±26 %) of TC in winter and summer, respectively. The contribution of secondary organic aerosol (SOA) to the organic mass (OM) was significant during the entire year. SOA accounted for 30 % (±16 %) and 85 % (±12 %) of OM during winter and summer, respectively. While the summer SOA was dominated by biogenic sources, winter SOA was mainly due to biomass burning and fossil sources. This indicates that the oxidation of semi-volatile and intermediate volatility organic compounds co-emitted with primary organics is a significant source of SOA, as suggested by recent model results and Aerosol Mass Spectrometer measurements. Comparison with previous global model simulations, indicates a strong underestimate of wintertime primary aerosol emissions in this region. The comparison of source apportionment results in different urban and rural areas showed that the sampling site was mainly affected by local aerosol sources during winter and regional air masses from the nearby Po Valley in summer. This observation was further confirmed by back-trajectory analysis applying the Potential Source Contribution Function method to identify potential source regions.

Primary anthropogenic aerosol emission trends for China, 1990–2005

Abstract. An inventory of anthropogenic primary aerosol emissions in China was developed for 1990–2005 using a technology-based approach. Taking into account changes in the technology penetration within industry sectors and improvements in emission controls driven by stricter emission standards, a dynamic methodology was derived and implemented to estimate inter-annual emission factors. Emission factors of PM2.5 decreased by 7%–69% from 1990 to 2005 in different industry sectors of China, and emission factors of TSP decreased by 18%–80% as well, with the measures of controlling PM emissions implemented. As a result, emissions of PM2.5 and TSP in 2005 were 11.0 Tg and 29.7 Tg, respectively, less than what they would have been without the adoption of these measures. Emissions of PM2.5, PM10 and TSP presented similar trends: they increased in the first six years of 1990s and decreased until 2000, then increased again in the following years. Emissions of TSP peaked (35.5 Tg) in 1996, while the peak of PM10 (18.8 Tg) and PM2.5 (12.7 Tg) emissions occurred in 2005. Although various emission trends were identified across sectors, the cement industry and biofuel combustion in the residential sector were consistently the largest sources of PM2.5 emissions, accounting for 53%–62% of emissions over the study period. The non-metallic mineral product industry, including the cement, lime and brick industries, accounted for 54%–63% of national TSP emissions. There were no significant trends of BC and OC emissions until 2000, but the increase after 2000 brought the peaks of BC (1.51 Tg) and OC (3.19 Tg) emissions in 2005. Although significant improvements in the estimation of primary aerosols are presented here, there still exist large uncertainties. More accurate and detailed activity information and emission factors based on local tests are essential to further improve emission estimates, this especially being so for the brick and coke industries, as well as for coal-burning stoves and biofuel usage in the residential sector.

Emission and dry deposition of accumulation mode particles in the Amazon Basin

Abstract. Size-resolved vertical aerosol number fluxes of particles in the diameter range 0.25–2.5 μm were measured with the eddy covariance method from a 53 m high tower over the Amazon rain forest, 60 km NNW of Manaus, Brazil. This study focuses on data measured during the relatively clean wet season, but a shorter measurement period from the more polluted dry season is used as a comparison. Size-resolved net particle fluxes of the five lowest size bins, representing 0.25–0.45 μm in diameter, were in general dominated by deposition in more or less all wind sectors in the wet season. This is an indication that the source of primary biogenic aerosol particles may be small in this particle size range. Transfer velocities within this particle size range were observed to increase linearly with increasing friction velocity and increasing particle diameter. In the diameter range 0.5–2.5 μm, vertical particle fluxes were highly dependent on wind direction. In wind sectors where anthropogenic influence was low, net upward fluxes were observed. However, in wind sectors associated with higher anthropogenic influence, deposition fluxes dominated. The net upward fluxes were interpreted as a result of primary biogenic aerosol emission, but deposition of anthropogenic particles seems to have masked this emission in wind sectors with higher anthropogenic influence. The net emission fluxes were at maximum in the afternoon when the mixed layer is well developed, and were best correlated with horizontal wind speed according to the equation log10 F=0.48 · U+2.21 where F is the net emission number flux of 0.5–2.5 μm particles [m−2 s−1] and U is the horizontal wind speed [ms−1] at the top of the tower.

Organic aerosol formation in citronella candle plumes.

Citronella candles are widely used as insect repellants, especially outdoors in the evening. Because these essential oils are unsaturated, they have a unique potential to form secondary organic aerosol (SOA) via reaction with ozone, which is also commonly elevated on summer evenings when the candles are often in use. We investigated this process, along with primary aerosol emissions, by briefly placing a citronella tealight candle in a smog chamber and then adding ozone to the chamber. In repeated experiments, we observed rapid and substantial SOA formation after ozone addition; this process must therefore be considered when assessing the risks and benefits of using citronella candle to repel insects.

Aerosol number fluxes over the Amazon rain forest during the wet season

Abstract. Number fluxes of particles with diameter larger than 10 nm were measured with the eddy covariance method over the Amazon rain forest during the wet season as part of the LBA (The Large Scale Biosphere Atmosphere Experiment in Amazonia) campaign 2008. The primary goal was to investigate whether sources or sinks dominate the aerosol number flux in the tropical rain forest-atmosphere system. During the measurement campaign, from 12 March to 18 May, 60% of the particle fluxes pointed downward, which is a similar fraction to what has been observed over boreal forests. The net deposition flux prevailed even in the absolute cleanest atmospheric conditions during the campaign and therefore cannot be explained only by deposition of anthropogenic particles. The particle transfer velocity vt increased with increasing friction velocity and the relation is described by the equation vt = 2.4×10−3×u* where u* is the friction velocity. Upward particle fluxes often appeared in the morning hours and seem to a large extent to be an effect of entrainment fluxes into a growing mixed layer rather than primary aerosol emission. In general, the number source of primary aerosol particles within the footprint area of the measurements was small, possibly because the measured particle number fluxes reflect mostly particles less than approximately 200 nm. This is an indication that the contribution of primary biogenic aerosol particles to the aerosol population in the Amazon boundary layer may be low in terms of number concentrations. However, the possibility of horizontal variations in primary aerosol emission over the Amazon rain forest cannot be ruled out.

Anthropogenic influence on SOA and the resulting radiative forcing

Abstract. The effect of chemical changes in the atmosphere since the pre-industrial period on the distributions and burdens of Secondary Organic Aerosol (SOA) has been calculated using the off-line aerosol chemistry transport model Oslo CTM2. The production of SOA was found to have increased from about 35 Tg yr−1 to 53 Tg yr−1 since pre-industrial times, leading to an increase in the global annual mean SOA burden from 0.33 Tg to 0.50 Tg, or about 51%. The effect of allowing semi-volatile species to partition to sulphate aerosol was also tested, leading to an increase in SOA production from about 43 Tg yr−1 to 69 Tg yr−1 since pre-industrial times, while the annual mean SOA burden increased from 0.44 Tg to 0.70 Tg, or about 59%. The increases were greatest over industrialised areas, especially when partitioning to sulphate aerosol was allowed, as well as over regions with high biogenic precursor emissions. The contribution of emissions from different sources to the larger SOA burdens has been calculated. The results suggest that the majority of the increase was caused by emissions of primary organic aerosols (POA), from fossil fuel and bio fuel combustion. As yet, very few radiative forcing estimates of SOA exist, and no such estimates were provided in the latest IPCC report. In this study, we found that the change in SOA burden caused a radiative forcing (defined here as the difference between the pre-industrial and the present day run) of −0.09 W m−2, when SOA was allowed to partition to both organic and sulphate aerosols, and −0.06 W m−2 when only partitioning to organic aerosols was assumed. Therefore, the radiative forcing of SOA was found to be stronger than the best estimate for POA in the latest IPCC assessment.

Seasonal and Diurnal Variation of PM2.5 Apparent Particle Density in Urban Air in Augsburg, Germany

The apparent particle density of particulate matter with aerodynamic diameter < 2.5 microm (rho2.5) was determined at an urban site in Augsburg, Germany and its correlation with chemical composition and meteorological conditions was investigated. rho2.5 showed strong day-to-day variation from 1.05 to 2.36 g cm(-3) (5 to 95% percentile), and nearly 64% of the daily variability could be explained by a multiple variable regression model. A minimum in the morning and afternoon (about 1.5 g cm(-3)), and a maximum (near 1.8 g cm(-3)) during midday was observed. The minima represent fresh primary aerosol emissions, which were related to traffic soot particles with low density due to their agglomerate structure, especially observed in the early morning hours of weekdays. The maximum is likely due to increased secondary particle production and the presence of more aged particles with the built-up of the convectively mixed boundary layer. rho2.5 has the potential to serve as a crude tracer for chemical composition and atmospheric processing and might play an important role when considering the associations between health effects and ambient particles.

Contributions of natural sources to high [formula omitted] and [formula omitted] events in the eastern Mediterranean

In total 562 daily PM 10 and PM 2.5 samples were collected from April 2001 to April 2002 at a rural site (Erdemli) located on the coast of the Eastern Mediterranean. The annual mean PM 10 and PM 2.5 levels were 36.4 ± 27.8 and 9.7 ± 5.9 μ g m - 3 , respectively. PM 10 and PM 2.5 concentrations indicated orders of magnitude change from day to day ( PM 10 = 2 – 326 μ g m - 3 ; PM 2.5 = 0.5 – 28 μ g m - 3 ). The highest levels of PM 10 were observed during the transition period (March, April and May) due to mineral dust transported from North Africa and during winter due to sea spray generation. However, PM 2.5 levels exhibited higher concentrations during summer resulting from an enhanced production of secondary aerosols. The PM 2.5 / PM 10 ratio (0.25) and categorization of air mass back trajectories indicated that PM 10 at the study area is dominated by primary aerosol emissions (mineral dust particles from the Saharan Desert and sea salt particles from the Mediterranean Sea itself). During the whole sampling period 28 and 51 events exceeded the recommended maximum values of 50 and 15 μ g m - 3 for PM 10 and PM 2.5 , respectively. Source apportionment analysis indicated that PM 10 exceedances originated as a consequence of natural events (mineral dust ∼ 40 % ; sea salt ∼ 50 % ) whereas PM 2.5 exceedances were accounted primarily by pollution events (in 90% of the cases).

Modelling and evaluation of size-resolved aerosol characteristics in the Eastern Mediterranean during the SUB-AERO project

The mesoscale air-quality modelling system UAM-AERO has been applied to study the dynamics of aerosols in the Eastern Mediterranean area. The objective of the current work is to validate the model against extensive field aerosol data for the realistic determination of the aerosol size distribution/chemical composition. The model has been studied against comprehensive aerosol size distribution data during the periods July 2000 and January 2001 at the Eastern Mediterranean area. Comparison of the model results with the field data shows that the model predicts a bimodal size distribution for the aerosol mass, which is in agreement with the experimental data, but underpredicts the total mass during the summer period, whereas the agreement for the total aerosol mass is better during the winter period. The model is capable of reproducing the size distribution characteristics of sulphate, ammonium and nitrate, but discrepancies have occurred in relation to their mass concentration during the period 26–30 July 2000. Discrepancies have also been observed in the determination of the size distribution characteristics of crustal aerosol mass and sea salt. The disagreement between the modelled results and the field data is attributed to uncertainties in the primary aerosol emissions such as sea salt and resuspended dust, and unresolved emissions from sources such as forest fires and Saharan dust episodes. It is evident that the use of the mesoscale model UAM-AERO in the Mediterranean area requires the parallel use of a regional model, which needs to incorporate emissions of Saharan dust and forest fires.

Simulation of secondary aerosols over North China in summer

The comparisons of observed and simulated NOx, CO, O3, NH3, HNO3, SO2 and PM2.5 indicate that CMAQ model can simulate variations of pollutants over North China well. Moreover, the model results show that high NH3 is in Hebei, Henan and Shandong provinces, with average concentration of (30-35)×10-9. The results of the sensitive experiment indicate that high concentration of NH3 has the efficiency of the production of secondary sulfate aerosol increase by more than 30%, especially at the juncture of Handan, Anyang and Changzhi that increased by 50%. In addition, NH3 also produces secondary ammonia and nitrate aerosol, and the sum of them is approximately equal to sulfate aerosol. The height of planetary boundary layer (PBL) in Beijing is higher in daytime, with average height of 1500 m at noon. This makes SO2, NH3 and HNO3 transported into upper PBL of 850 hPa. The high secondary sulfate, and ammonia and nitrate aerosol happen in the upper and lower PBL, respectively. Because PM2.5 lifetime is relatively long, it can be transported into the middle troposphere to form a thick aerosol layer, which is the arched roof of aerosol. The model result suggests that if the aerosol concentration in North China would be controlled, the reduction of NH3 emission is one of efficient ways besides the reduction of primary SO2, NOx and aerosol emission.

Chemical evolution of an isolated power plant plume during the TexAQS 2000 study

Abstract Stack emissions from a coal-burning power plant were measured during a research flight of the DOE G-1 during the Texas Air Quality Study (TexAQS 2000) on 10 September 2000. Clean upstream air and an isolated location allowed the plume to be unambiguously sampled during 12 successive downwind transects to a distance of 63 km—corresponding to a processing time of 4.6 h. The chemical transformation rates of sulfur and nitrogen primary pollutants into aerosol SO 4 2 - and HNO 3 yield independent values of OH concentration (8.0 and 11 × 10 6 cm - 3 , respectively) that are consistent within experimental uncertainty and qualitatively agree with constrained steady-state (CSS) box model calculations. Ozone production efficiency increases with plume age as expected. Primary aerosol emissions with D p > 5 μ m were sampled near the stack. As the plume ages, aerosol size distributions adjusted for dilution show constant number concentrations of aerosols D p > 10 nm and a marked increase in accumulation-mode particles ( D p > 0.1 μ m) as gas-to-particle-conversion causes smaller particles to grow.

Spatial distribution and size evolution of particles in Asian outflow: Significance of primary and secondary aerosols during ACE‐Asia and TRACE‐P

Quasi‐Lagrangian aircraft measurements above the Yellow Sea, East China Sea, and Sea of Japan revealed synoptic‐scale secondary aerosol formation and condensational growth during the Asian Pacific Regional Aerosol Characterization Experiment (ACE‐Asia) and Transport and Chemical Evolution over the Pacific (TRACE‐P) experiment. This occurred in the presence of pollution and mineral dust aerosol surface areas as high as 1200 μm2 cm−3. Concentrations of sulfuric acid generally appeared insufficient for binary nucleation, but observations, models, and theory are consistent with a ternary nucleation mechanism involving H2SO4‐H2O‐NH3. Growth rates of ∼2 nm h−1 can be explained by the condensation of sulfuric acid at a rate of 2 ± 1 × 106 molecules cm−3 s−1. Aerosol volatility suggested increasing neutralization of the aerosol during growth. Size distribution measurements suggest that weak (mean condensation nuclei (CN) 3–13 nm ≈ 500 cm−3) new particle production was a common occurrence in the region. However, new particle production was enhanced by ∼1 order of magnitude (mean CN 3–13 nm ≈ 5000 cm−3) in postfrontal air masses associated with offshore flow during cloud‐free conditions. Fog and clouds appear to be regionally important in modulating nucleation events through scavenging of secondary aerosol and through depletion of gas‐phase precursors through enhanced heterogeneous chemistry. Our results indicate that only 10–30% of the total aerosol population consists of aged secondary aerosols after ∼2 days of transport from source regions. In spite of their high production during nucleation events, secondary aerosols advected out over the Pacific Ocean will have a small impact upon indirect forcing and a negligible impact upon direct forcing compared to primary aerosol emissions and the species that condense upon them.

An inventory of gaseous and primary aerosol emissions in Asia in the year 2000

An inventory of air pollutant emissions in Asia in the year 2000 is developed to support atmospheric modeling and analysis of observations taken during the TRACE‐P experiment funded by the National Aeronautics and Space Administration (NASA) and the ACE‐Asia experiment funded by the National Science Foundation (NSF) and the National Oceanic and Atmospheric Administration (NOAA). Emissions are estimated for all major anthropogenic sources, including biomass burning, in 64 regions of Asia. We estimate total Asian emissions as follows: 34.3 Tg SO2, 26.8 Tg NOx, 9870 Tg CO2, 279 Tg CO, 107 Tg CH4, 52.2 Tg NMVOC, 2.54 Tg black carbon (BC), 10.4 Tg organic carbon (OC), and 27.5 Tg NH3. In addition, NMVOC are speciated into 19 subcategories according to functional groups and reactivity. Thus we are able to identify the major source regions and types for many of the significant gaseous and particle emissions that influence pollutant concentrations in the vicinity of the TRACE‐P and ACE‐Asia field measurements. Emissions in China dominate the signature of pollutant concentrations in this region, so special emphasis has been placed on the development of emission estimates for China. China's emissions are determined to be as follows: 20.4 Tg SO2, 11.4 Tg NOx, 3820 Tg CO2, 116 Tg CO, 38.4 Tg CH4, 17.4 Tg NMVOC, 1.05 Tg BC, 3.4 Tg OC, and 13.6 Tg NH3. Emissions are gridded at a variety of spatial resolutions from 1° × 1° to 30 s × 30 s, using the exact locations of large point sources and surrogate GIS distributions of urban and rural population, road networks, landcover, ship lanes, etc. The gridded emission estimates have been used as inputs to atmospheric simulation models and have proven to be generally robust in comparison with field observations, though there is reason to think that emissions of CO and possibly BC may be underestimated. Monthly emission estimates for China are developed for each species to aid TRACE‐P and ACE‐Asia data interpretation. During the observation period of March/April, emissions are roughly at their average values (one twelfth of annual). Uncertainties in the emission estimates, measured as 95% confidence intervals, range from a low of ±16% for SO2 to a high of ±450% for OC.

Global modelling of secondary organic aerosol in the troposphere: a sensitivity analysis

Abstract. A global 3-dimensional chemistry/transport model able to describe O3, NOx, Volatile Organic Compounds (VOC), sulphur and NH3 chemistry has been extended to simulate the temporal and spatial distribution of primary and secondary carbonaceous aerosols in the troposphere focusing on Secondary Organic Aerosol (SOA) formation. A number of global simulations have been performed to determine a possible range of annual global SOA production and investigate uncertainties associated with the model results. The studied uncertainties in the SOA budget have been evaluated to be in decreasing importance: the potentially irreversible sticking of the semi-volatile compounds on aerosols, the enthalpy of vaporization of these compounds, the partitioning of SOA on non-carbonaceous aerosols, the conversion of aerosols from hydrophobic to hydrophilic, the emissions of primary carbonaceous aerosols, the chemical fate of the first generation products and finally the activity coefficient of the condensable species. The large uncertainties associated with the emissions of VOC and the adopted simplification of chemistry have not been investigated in this study. Although not all sources of uncertainties have been investigated, according to our calculations, the above factors within the experimental range of variations could result to an overall uncertainty of about a factor of 20 in the global SOA budget. The global annual SOA production from biogenic VOC might range from 2.5 to 44.5 Tg of organic matter per year, whereas that from anthropogenic VOC ranges from 0.05 to 2.62 Tg of organic matter per year. These estimates can be considered as a lower limit, since partitioning on coarse particles like nitrate, dust or sea-salt, together with the partitioning and the dissociation of the semi-volatile products in aerosol water has been neglected. Comparison of model results to observations, where available, shows a better agreement for the upper budget estimates than for the lower ones.

Acid effects in inductively coupled plasma atomic emission spectrometry with different nebulizers operated at very low sample consumption rates

The acid interference effects observed in inductively coupled plasma atomic emission spectrometry (ICP-AES) for three different nebulizers at sub-millilitre liquid flow rates were investigated. The nebulizers studied were a microconcentric nebulizer (MCN), a pneumatic concentric nebulizer and a conespray nebulizer. Five different matrices were studied: water and solutions containing 0.9 and 3.6 m nitric and sulfuric acid. Primary and tertiary aerosol drop size distributions and ICP-AES emission intensities were measured for all the nebulizers and solutions at liquid flow rates (Ql) ranging from 0.03 to 0.6 ml min–1. A study of the acid effect as a function of the tertiary aerosol drop size was carried out through a laboratory-made impactor device. The results indicate that finer primary and tertiary aerosols are generated as Ql is reduced. Primary aerosols originating from nitric acid and water have similar drop size distributions, whereas they become coarser when sulfuric acid is used. In contrast, acids generate, under all the conditions studied, tertiary aerosols that have a higher proportion of small droplets than water. The results also demonstrate that the MCN gives rise to finer primary and tertiary aerosols than the other two nebulizers. The studies concerning the analytical signal reveal that, for all the acid solutions, a drop in the ICP-AES emission intensity is produced with respect to water. The magnitude of this signal depression depends on the liquid flow rate (i.e., the lower the Ql the higher the signal drop) and on the acid solution employed. The measurements performed with the impactor device have demonstrated that, for the same nebulizer, the acid effects are more pronounced as the proportion of small droplets increases. Accordingly, it was observed that the drain analyte concentration is higher than that found in the tertiary aerosols. As a result, a phenomenon such as aerosol ionic redistribution is expected to contribute to the interferences when acid solutions are analyzed by ICP-AES.

Contribution of primary aerosol emissions from vegetation‐derived sources to fine particle concentrations in Los Angeles

Field measurements of the n‐alkanes present in fine atmospheric aerosols show a predominance of odd carbon numbered higher molecular weight homologues (C27–C33) that is characteristic of plant waxes. Utilizing a local leaf wax n‐alkane profile in conjunction with an air quality model, it is estimated that, at most, 0.2–1.0 μg m−3 of the airborne fine particulate matter (dp &lt; 2.1 μm) present in the Los Angeles basin could originate from urban vegetative detritus; this corresponds to approximately 1–3% of the total ambient fine aerosol burden. However, some of the observed vegetation aerosol fingerprint in the Los Angeles air may be due in part to emissions from food cooking rather than plant detritus. Seasonal trends in the ambient n‐alkane patterns are examined to seek further insight into the relative importance of anthropogenic versus natural sources of vegetation‐derived fine particulate matter.

Mathematical modeling of urban organic aerosol: properties measured by high-resolution gas chromatography

Primary fine aerosol emissions from a variety of urban sources have been quantitatively characterized via high-resolution gas chromatography to obtain organic mass distribution fingerprints. To assess the degree of secondary organic aerosol formation in urban areas, a transport model is used to predict the distribution of ambient organic aerosol characteristics that would exist at various sites in the Los Angeles Basin if the primary organic emissions were transported without chemical reaction. Comparisons between the model predictions and ambient measurements show substantial agreement for the nonpolar organics, suggesting that ambient concentrations of this organic fraction result directly from primary emissions. In contrast, ambient concentrations of fine acidic organic aerosols are significantly underpredicted by the model, indicating that secondary formation is important for acidic organics. On the basis of the observed differences between model predictions and measured properties of acidic organics, it is estimated, using monthly averages, that up to 18-27 % of the elutable organic aerosol present in the Los Angeles atmosphere may be secondary in origin.