Receptor modeling of PM2.5, PM10 and TSP in different seasons and long-range transport analysis at a coastal site of Tianjin, China

Atmospheric particulate matter (PM_2.5, PM₁₀ and TSP) were sampled synchronously during three monitoring campaigns from June 2007 to February 2008 at a coastal site in TEDA of Tianjin, China. Chemical compositions including 19 elements, 6 water-solubility ions, organic and elemental carbon were determined. principle components analysis (PCA) and chemical mass balance modeling (CMB) were applied to determine the PM sources and their contributions with the assistance of NSS SO₄²⁻, the mass ratios of NO₃⁻ to SO₄²⁻ and OC to EC. Air mass backward trajectory model was compared with source apportionment results to evaluate the origin of PM. Results showed that NSS SO₄²⁻ values for PM_2.5 were 2147.38, 1701.26 and 239.80 ng/m³ in summer, autumn and winter, reflecting the influence of sources from local emissions. Most of it was below zero in summer for PM₁₀ indicating the influence of sea salt. The ratios of NO₃⁻ to SO₄²⁻ was 0.19 for PM_2.5, 0.18 for PM₁₀ and 0.19 for TSP in winter indicating high amounts of coal consumed for heating purpose. Higher OC/EC values (mostly larger than 2.5) demonstrated that secondary organic aerosol was abundant at this site. The major sources were construction activities, road dust, vehicle emissions, marine aerosol, metal manufacturing, secondary sulfate aerosols, soil dust, biomass burning, some pharmaceutics industries and fuel-oil combustion according to PCA. Coal combustion, marine aerosol, vehicular emission and soil dust explained 5-31%, 1-13%, 13-44% and 3-46% for PM_2.5, PM₁₀ and TSP, respectively. Backward trajectory analysis showed air parcels originating from sea accounted for 39% in summer, while in autumn and winter the air parcels were mainly related to continental origin.     

Seasonal variations of elemental carbon in urban aerosols as measured by two common thermal-optical carbon methods

Two commonly employed laboratory-based elemental carbon (EC) and organic carbon (OC) thermal/optical methods for the analysis of ambient particulate matter were used to analyze 709 twenty-four hour integrated PM_2.5 samples along with 76 field blanks from the St. Louis-Midwest Supersite in East St. Louis, Illinois. The two laboratory ECOC methods were the Aerosol Characterization Experiment—Asia (ACE-Asia) method based on National Institute of Occupational Safety and Health (NIOSH 5040) method and the Interagency Monitoring of Protected Visual Environments (IMPROVE) protocol. As in previous intercomparisons between these two methods, there was excellent agreement for total carbon (i.e. sum of EC and OC), but significant differences were observed in the split between the measured EC and OC. The 709 daily PM_2.5 samples spanned a time series of two years that allowed an assessment of seasonal relationships between the EC reported by the two methods. Seasonal average ACE-Asia and IMPROVE EC concentration values were highest in the fall and lowest in the spring. Differences between the seasonal average IMPROVE and ACE-Asia EC concentration values were about 40% greater in summer compared to winter. While IMPROVE EC values were always larger than ACE-Asia EC, the EC difference between these methods exhibited a strong seasonal variation with largest differences occurring in the spring and especially summer with the smallest differences in the fall and winter. Seasonal average EC differences (IMPROVE − ACE-Asia) were anti-correlated with molecular markers for biomass burning and mobile source emissions that had wintertime maximum concentrations. The EC difference between methods did have a moderate positive correlation with indicators of secondary organic aerosol and sulfate suggesting that oxidized organic aerosol associated with atmospheric processing or other secondary components of ambient aerosol could be associated with the seasonal differences between these EC measurements.     

Aerosol chemical composition over Istanbul

This study examines the chemical composition of aerosols over the Greater Istanbul Area. To achieve this 325 (PM₁₀) aerosol samples were collected over Bosphorus from November 2007 to June 2009 and were analysed for the main ions, trace metals, water-soluble organic carbon (WSOC), organic (OC) and elemental carbon (EC).PM₁₀ levels were found to be in good agreement with those measured by the Istanbul Municipality air quality network, indicating that the sampling site is representative of the Greater Istanbul Area. The main ions measured in the PM₁₀ samples were Na⁺, Ca²⁺ and non-sea-salt sulphates (nss-SO₄²⁻). On average, 31% of Ca²⁺ was found to be associated with carbonates. Trace elements related to human activities (as Pb, V, Cd and Ni) obtained peak values during winter due to domestic heating, whereas natural origin elements like Al, Fe and Mn peaked during the spring period due to dust transport from Northern Africa. Organic carbon was found to be mostly primary and elemental carbon was strongly linked to fuel oil combustion and traffic. Both OC and EC concentrations increased during winter due to domestic heating, while the higher WSOC to OC ratio during summer can be mostly attributed to the presence of secondary, oxidised and more soluble organics. Factor analysis identified six components/sources for aerosol species in PM₁₀, namely traffic/industrial, crustal, sea-salt, fuel-oil combustion, secondary and ammonium sulfate.     

Pollution situation and possible markers of different sources in the Ordos Region, Inner Mongolia, China

In order to investigate the pollution situation for a fast-developing industrial area at its first stage, a systematic study on the gaseous and particulate pollution in the Ordos Region of Inner Mongolia was performed during 9-24 September 2005. The gases SO₂, NO_x, O₃, CO, and the particulates PM₁₀ and PM_2.5 were sampled at five sites in Ordos. Species measured in aerosol were 21 elements, 10 ions, organic carbon (OC), elemental carbon (EC), and the acid-buffering capacity of particulates. Possible markers of sources for different transport directions were firstly investigated, which was a new attempt for clarification of regional transport with different directions. None of the gases exceeded the national standards of China. PM_2.5 contributed most to PM₁₀ at the background site, indicating the greatest contribution of regional transport. Organic matter, crustal material, and sulfate ion were the three dominant species of aerosol, followed by EC, NO₃⁻, NH₄⁺, trace elements, and other ions. The acidity of PM_2.5 was higher than that of PM₁₀, and the buffering capacity in PM₁₀ was higher than that in PM_2.5. Four peaks of pollution aerosol were observed during the 3-week study sampling period, separated by periods of cleaner air. Back-trajectories revealed that the peaks came from the south and the cleaner air from the north. It is the first time to find different markers for aerosols from different transport directions in Ordos. S and Pb, as well as SO₄²⁻, NO₃⁻, and NH₄⁺ appeared to be good markers of southern aerosol in the Ordos, since all showed four clear peaks on days dominated by southern direction. Extremely high peaks of Al and Ti on the 16th and 17th, especially at the dust-monitoring site, indicated good markers for soil dust. Ca and Mg showed earlier peaks on the 16th at the western site, indicating possible markers for western aerosol.     

Organic compounds of PM2.5 in Mexico Valley: spatial and temporal patterns, behavior and sources

A longitudinal study on spatial and temporal behavior of particles less than 2.5 μm (PM_2.5), solvent extracted organic matter (SEOM), polycyclic aromatic hydrocarbons (PAH), n-alkanes and nitro-PAH was carried out for a full year in 2006, at five sites simultaneously around the Metropolitan Zone of Mexico Valley (MZMV). There is rather uniform distribution of PM_2.5 and SEOM in the MZMV regarding gravimetric mass concentration, while some specific organic chemical components showed mass heterogeneity. The highest mass concentrations of target compounds occurred in the dry seasons with respect to the rainy season. Bonfires and fireworks are probably responsible for extreme values of PM_2.5, SEOM and PAH (≥ 228 g mol^− 1). Benzo[ghi]perylene was the most abundant PAH, with C₂₄-C₂₆ the most abundant n-alkanes and 2-nitrofluoranthene and 9-nitroanthracene the most abundant nitro-PAH. The northeast zone was the area with the greatest presence of sources of incomplete diesel combustion, while the central for gasoline combustion. In the southwest, the biogenic sources were more abundant over the anthropogenic sources. This was opposite to the other sites. Factor analysis allowed us to relate different compounds to emitting sources. Three main factors were associated with combustion, pyrolysis and biogenic primary sources while the other factors were associated with secondary organic aerosol formation and industry. Correlation analyses indicated that SEOM originates from different primary emission sources or is formed by different processes than the other variables, except in southwest. Associations among variables suggest that PM_2.5 in the northwest and in the southeast originated mainly from primary emissions or consisted of primary organic compounds. PM_2.5 in the northeast, central and southwest contains a greater proportion of secondary organic compounds, with the less oxidized organic aerosols in the northeast and the most aged organic aerosol in the southwest. This follows the trends in the prevailing wind directions in MZMV during 2006.     

Emission of trace gases and organic components in smoke particles from a wildfire in a mixed-evergreen forest in Portugal

On May 2009, both the gas and particulate fractions of smoke from a wildfire in Sever do Vouga, central Portugal, were sampled. Total hydrocarbons and carbon oxides (CO₂ and CO) were measured using automatic analysers with flame ionisation and non-dispersive infrared detectors, respectively. Fine (PM_2.5) and coarse (PM_2.5-10) particles from the smoke plume were analysed by a thermal-optical transmission technique to determine the elemental and organic carbon (EC and OC) content. Subsequently, the particle samples were solvent extracted and fractionated by vacuum flash chromatography into different classes of organic compounds. The detailed organic speciation was performed by gas chromatography-mass spectrometry. The CO, CO₂ and total hydrocarbon emission factors (g kg⁻¹ dry fuel) were 170 ± 83, 1485 ± 147, and 9.8 ± 0.90, respectively. It was observed that the particulate matter and OC emissions are significantly enhanced under smouldering fire conditions. The aerosol emissions were dominated by fine particles whose mass was mainly composed of organic constituents, such as degradation products from biopolymers (e.g. levoglucosan from cellulose, methoxyphenols from lignin). The compound classes also included homologous series (n-alkanes, n-alkenes, n-alkanoic acids and n-alkanols), monosaccharide derivatives from cellulose, steroid and terpenoid biomarkers, and polycyclic aromatic hydrocarbons (PAHs). The most abundant PAH was retene. Even carbon number homologs of monoglycerides were identified for the first time as biomarkers in biomass burning aerosols.     

Wood stove use and other determinants of personal and indoor exposures to particulate air pollution and ozone among elderly persons in a Northern Suburb

A six‐month winter‐spring study was conducted in a suburb of the northern European city of Kuopio, Finland, to identify and quantify factors determining daily personal exposure and home indoor levels of fine particulate matter (PM_2.5, diameter <2.5 µm) and its light absorption coefficient (PM_2.5abs), a proxy for combustion‐derived black carbon. Moreover, determinants of home indoor ozone (O₃) concentration were examined. Local central site outdoor, home indoor, and personal daily levels of pollutants were monitored in this suburb among 37 elderly residents. Outdoor concentrations of the pollutants were significant determinants of their levels in home indoor air and personal exposures. Natural ventilation in the detached and row houses increased personal exposure to PM_2.5, but not to PM_2.5abs, when compared with mechanical ventilation. Only cooking out of the recorded household activities increased indoor PM_2.5. The use of a wood stove room heater or wood‐fired sauna stove was associated with elevated concentrations of personal PM_2.5 and PM_2.5abs, and indoor PM_2.5abs. Candle burning increased daily indoor and personal PM_2.5abs, and it was also a determinant of indoor ozone level. In conclusion, relatively short‐lasting wood and candle burning of a few hours increased residents’ daily exposure to potentially hazardous, combustion‐derived carbonaceous particulate matter.     

Polar organic and inorganic markers in PM10 aerosols from an inland city of China — Seasonal trends and sources

Polar organic compounds and elements were quantified in PM₁₀ aerosols collected in urban and rural areas of Baoji, an inland city of China, during winter and spring 2008. Concentrations of biomass burning markers and high molecular weight n-alkanoic acids (HMW, > C_22:0) were heavily increased in winter. In contrast, sugars presented in higher levels in the spring, among which sucrose was the most abundant with an average of 219 ng m⁻³ in winter and 473 ng m⁻³ in spring respectively. This suggests enhanced biotic activity in the warm season, whereas no obvious trend was observed for sugar alcohols, concentrations of the three sugar alcohols in spring were only 0.94-2.3 times as those in winter, indicating a second pathway of their formation other than fungal spores in cold season. Major crustal elements (i.e., Fe, K, Mn and Ti) in PM₁₀ aerosols were also observed in larger concentrations in spring samples than those in winter due to an enhancement of coarse particles from soil minerals. By using principal component analysis (PCA) and positive matrix factorization (PMF), sources and their contributions to the PM components were also investigated in this study. Four factors were extracted with both models, and the sources represented by different factors were based on the highest loaded marker species as follows: factor 1, soil and road dust (Fe, Sr and Ti); factor 2, biomass burning (levoglucosan, galactosan and syringic acid); factor 3, microbial emissions (fructose and sucrose); and factor 4, fossil fuel combustion and fungal spores influence (Pb, Zn, arabitol and mannitol). The high correlation between PM₁₀ and factor 1 suggested that PM₁₀ pollution in Baoji was dominated by soil and dust re-suspension.     

Seasonal pollution characteristics of organic compounds in atmospheric fine particles in Beijing

Beijing is a rapidly developing city with severe and unique air pollution problems. Organic matter is the most abundant fraction in fine particles in Beijing, occupying 30-50% of the total mass, indicating its key role in air pollution control. However, detailed chemical characterization of particulate organic matter in Beijing has never been reported. In this study, fine particles in the urban atmosphere in Beijing were investigated for its organic components by GC/MS technique. Over 100 individual organic compounds were identified and quantified in 25 PM2.5 samples from the summer, autumn and winter of 2002-2003. Alkanes, fatty acids, dicarboxylic acids, polycyclic aromatic hydrocarbons and some important tracer compounds (hopanes, levoglucosan and steroids) were the major constituents with the sum of their concentrations of 502, 1471 and 1403 ng m(-3) in summer, autumn and winter, respectively. Different organic compounds presented apparently different seasonal characteristics, reflecting their different dominant emission sources, such as coal combustion, biomass burning and cooking emission. The abundance and origin of these organic compounds are discussed to reveal seasonal air pollution characteristics of Beijing.     

Outdoor,indoor, and personal black carbon exposure from cookstoves burning solid fuels

Black carbon (BC) emissions from solid fuel combustion are associated with increased morbidity and mortality and are important drivers of climate change. We studied BC measurements, approximated by particulate matter (PM_2.5) absorbance, in rural Yunnan province, China, whose residents use a variety of solid fuels for cooking and heating including bituminous and anthracite coal, and wood. Measurements were taken over two consecutive 24‐h periods from 163 households in 30 villages. PM_2.5 absorbance (PM_abs) was measured using an EEL 043 Smoke Stain Reflectometer. PM_abs measurements were higher in wood burning households (16.3 × 10^?5/m) than bituminous and anthracite coal households (12 and 5.1 × 10^?5/m, respectively). Among bituminous coal users, measurements varied by a factor of two depending on the coal source. Portable stoves (which are lit outdoors and brought indoors for use) were associated with reduced PM_abs levels, but no other impact of stove design was observed. Outdoor measurements were positively correlated with and approximately half the level of indoor measurements (r = 0.49, P < 0.01). Measurements of BC (as approximated by PM_abs) in this population are modulated by fuel type and source. This provides valuable insight into potential morbidity, mortality, and climate change contributions of domestic usage of solid fuels.     

Impacts of stove/fuel use and outdoor air pollution on chemical composition of household particulate matter

Biomass combustion for cooking and heating releases particulate matter (PM_2.5) that contributes to household air pollution. Fuel and stove types affect the chemical composition of household PM, as does infiltration of outdoor PM. Characterization of these impacts can inform future exposure assessments and epidemiologic studies, but is currently limited. In this study, we measured chemical components of PM_2.5 (water-soluble organic matter [WSOM], ions, black carbon, elements, organic tracers) in rural Chinese households using traditional biomass stoves, semi-gasifier stoves with pelletized biomass, and/or non-biomass stoves. We distinguished households using one stove type (traditional, semi-gasifier, or LPG/electric) from those using multiple stoves/fuels. WSOM concentrations were higher in households using only semi-gasifier or traditional stoves (31%-33%) than in those with exclusive LPG/electric stove (13%) or mixed stove use (12%-22%). Inorganic ions comprised 14% of PM in exclusive LPG/electric households, compared to 1%-5% of PM in households using biomass. Total PAH content was much higher in households that used traditional stoves (0.8-2.8 mg/g PM) compared to those that did not (0.1-0.3 mg/g PM). Source apportionment revealed that biomass burning comprised 27%-84% of PM_2.5 in households using biomass. In all samples, identified outdoor sources (vehicles, dust, coal combustion, secondary aerosol) contributed 10%-20% of household PM_2.5.     

Characteristics of carbonaceous aerosols in ambient PM10 and PM2.5 particles in Dar es Salaam, Tanzania

Ambient daytime and nighttime PM₁₀ and PM_2.5 samples were collected in parallel at a kerbside in Dar es Salaam in August and September 2005 (dry season) and in April and May 2006 (wet season). All samples were analyzed for the particulate matter mass, for organic, elemental, and total carbon (OC, EC, and TC), and for water-soluble OC (WSOC). The average PM₁₀ and PM_2.5 mass concentrations and associated standard deviations were 76 ± 32 µg/m³ and 26 ± 7 µg/m³ for the 2005 dry season and 52 ± 27 µg/m³ and 19 ± 10 µg/m³ for the 2006 wet season campaign. On average, TC accounted for 29% of the PM₁₀ mass and 49% of the PM_2.5 mass for the 2005 dry season campaign and the corresponding values for the 2006 wet season campaign were 35% and 59%. There was little difference between the two campaigns for the WSOC/OC ratios with the PM_2.5 fraction having higher ratios than the PM₁₀ fraction during each campaign. Also for EC/TC higher ratios were noted in PM_2.5 than in PM₁₀, but the ratios were substantially larger in the 2006 wet season than in the 2005 dry season. The large EC/TC ratios (means 0.22-0.38) reflect the substantial impact from traffic at Dar es Salaam, as was also apparent from the clear diurnal variation in OC levels, with higher values during the day. A simple source apportionment approach was used to apportion the OC to traffic and charcoal burning. On average, 70% of the PM₁₀ OC was attributed to traffic and 30% to charcoal burning in both campaigns. A definite explanation for the substantially larger EC/TC ratios in the 2006 campaign as compared to the 2005 campaign is not available.     

Origins of n-alkanes, carbonyl compounds and molecular biomarkers in atmospheric fine and coarse particles of Athens, Greece

The abundance and origin of aliphatic hydrocarbons, carbonyl compounds and molecular biomarkers found in the aliphatic fraction of PM_10-2.5 and PM_2.5 in the centre of Athens Greece are discussed in an attempt to reveal seasonal air pollution characteristics of the conurbation. Each extract was fractionated into individual compound classes and was analyzed using gas chromatography coupled to mass spectrometry. Normal alkanes, ranging from C₁₄ to C₃₅, were abundant in PM_10-2.5 and PM_2.5 samples during both sampling campaigns. The daily concentration of total n-alkanes was up to 438 ng m^− 3 for PM_10-2.5 and up to 511 ng m^− 3 for PM_2.5. Additionally, gaseous concentrations of n-alkanes were calculated, revealing that the relative proportions between gaseous and particle phases of individual compounds may differ significantly between summer and late winter. Normal alkanals and alkan-2-ones were only detected in the fine fraction of particulate matter and their concentrations were much lower than the n-alkane concentrations. Several geochemical parameters were used to qualitatively reconcile the sources of organic aerosol. The carbon preference index (CPI) of the coarse particles in August had the highest value, while in March the leaf wax contribution decreased significantly and the CPI value was very close to unity for both sites. Maximum concentrations of carbonyl compounds were reported in the range of C₁₅-C₂₀, demonstrating that they were formed from anthropogenic activity or from atmospheric oxidative processes. 6, 10, 14-trimethylpentadecan-2-one, a marker of biogenic input, was also detected in our samples. Molecular biomarker compounds confirmed that ca. 60% of the aliphatic fraction on the sampled atmospheric particles originated from petroleum and not from any contemporary biogenic sources. Pristane and phytane were detected in the fine fraction with their presence indicating sources of fossil fuel in the range of C₁₆-C₂₀. At all sites the 17α(Η),21β(Η) hopane series was the most abundant hopane group.     

Characterization of fine particle emissions from incense burning

Incense burning is an important indoor source of airborne particles. In this study, the emission factors of PM_2.5 and its chemical constituents emitted from six different brands of incense sticks were determined. Controlled experiments were conducted to measure the mass concentration of PM_2.5 and to determine its chemical composition (elemental carbon (EC), organic carbon (OC), metals, and ions). Measurements showed that the emissions vary for different brands of incense sticks, with smokeless incense sticks emitting the least amount. PM_2.5 emission factors range from 0.4 (smokeless incense stick) to 44.5 mg/g. Results also show that the amount of metals emitted is highly dependent on the quantity of metals present in the incense sticks. In addition, the information obtained from the controlled experiments is used to predict the concentration of PM_2.5 at incense smoke-influenced microenvironments, such as temples and homes, in order to assess the potential indoor exposure during the course of incense burning. Comparison with indoor air quality guidelines suggests that inhalation of incense smoke can pose adverse health impacts.     

HVAC air-quality model and its use to test a PM2.5 control strategy

This paper presents a MATLAB^® Simulink air-quality model of a commercial building with a heating, ventilation, and air conditioning (HVAC) system in Fairbanks, Alaska. Outdoor and indoor real-time fine particulate matter (PM_2.5) levels were measured at this building during a summer wild-fire smoke episode and then during a winter period. The correlation coefficient between the model-predicted and the measured indoor concentrations was 0.99 for the summer and 0.98 for the winter, justifying the usability of the model for further studies. An HVAC control algorithm was developed that reduces the indoor PM_2.5 levels. The algorithm was tested using the HVAC Simulink model and the outdoor PM_2.5 data from the summer smoke episode. The average indoor PM_2.5 level with this control algorithm was 65% lower than with the regular control. Thanks to the PM_2.5 control strategy being automatically engaged only during episodes, it was shown to have the potential of significantly reducing the indoor PM_2.5 levels without significantly compromising the purpose of the original control strategy.     

Real-time characterization of aerosol particle composition,sources and influences of increased ventilation and humidity in an office

Most of human exposure to atmospheric pollutants occurs indoors, and the components of outdoor aerosols may have been changed in the way before reaching indoor spaces. Here we conducted real-time online measurements of mass concentrations and chemical composition of black carbon and the non-refractory species in PM_2.5 in an occupied office for approximately one month. The open-close windows and controlled dampness experiments were also performed. Our results show that indoor aerosol species primarily originate from outdoors with indoor/outdoor ratio of these species typically less than unity except for certain organic aerosol (OA) factors. All aerosol species went through filtration upon transport indoors. Ammonium nitrate and fossil fuel OA underwent evaporation or particle-to-gas partitioning, while less oxidized secondary OA (SOA) underwent secondary formation and cooking OA might have indoor sources. With higher particulate matter (PM) mass concentration outdoors than in the office, elevated natural ventilation increased PM exposure indoors and this increased exposure was prolonged when outdoor PM was scavenged. We found that increasing humidity in the office led to higher indoor PM mass concentration particularly more oxidized SOA. Overall, our results highlight that indoor exposure of occupants is substantially different from outdoor in terms of mass concentrations and chemical species.     

Carbonaceous characteristics of atmospheric particulate matter in Hong Kong

To determine the characteristic of carbonaceous species in atmospheric particles in Hong Kong, PM₁₀ and PM_2.5 samples were collected using high volume (hi-vol.) air samplers from November 2000 to February 2001. The organic carbon (OC) and elemental carbon (EC) were analyzed by the selective thermal manganese dioxide oxidation (TMO) method. The ratios of PM_2.5/PM₁₀ mass ratios were 0.61, 0.78 and 0.53 for particulate matter collected at PolyU station (PolyU, near a major traffic corridor), Kwun Tong station (KT, mixed residential/commercial/industrial) and the Hok Tsui background station (HT), respectively. These results indicate that the PM_2.5 concentrations constitute the majority of the PM₁₀ concentrations, especially in urban and industrial areas of Hong Kong. The average concentrations at the three sites ranged from 73.11 to 83.52 μg/m³ for PM₁₀ and from 42.37 to 57.38 μg/m³ for PM_2.5. The highest daily mass concentrations of PM₁₀ and PM_2.5 were 125.89 μg/m³ and 116.89 μg/m³ at KT, respectively. The correlation between PM₁₀ and PM_2.5 was high at KT and HT (r>0.9, P<0.01). This means that the sources of PM₁₀ and PM_2.5 may be the same at both sites. The highest mean concentration of OC (12.02 μg/m³) and EC (6.86 μg/m³) in PM₁₀ was found at the PolyU among the three sites. For PM_2.5, the highest mean concentration of OC (10.16 μg/m³) was at KT while the highest mean concentration of EC (7.95 μg/m³) was at PolyU. However, the background concentrations at HT were higher than another background area, Kosan, Korea. Transportation of pollutants from the Asian continent may be responsible for the elevations of EC+OC at the remote site. More than 74% of the EC and more than 79% of the OC were found in the PM_2.5 fraction at the three sampling locations. At PolyU station, PM_2.5 consisted of 18.18% OC and 11.16% EC while 17.70% OC and 8.81% EC were found in KT station. Thus OC and EC are major constituents of aerosols in Hong Kong. OC/EC ratios for PM₁₀ and PM_2.5 were less than 2 at PolyU and KT stations while the ratio exceeded 3 at HT background station. This indicates that OC measured in the urban area may be emitted directly as a primary aerosol.     

Personal exposure to PM2.5 in Chinese rural households in the Yangtze River Delta

High levels of PM_2.5 exposure and associated health risks are of great concern in rural China. For this study, we used portable PM_2.5 monitors for monitoring concentrations online, recorded personal time‐activity patterns, and analyzed the contribution from different microenvironments in rural areas of the Yangtze River Delta, China. The daily exposure levels of rural participants were 66 μg/m³ (SD 40) in winter and 65 μg/m³ (SD 16) in summer. Indoor exposure levels were usually higher than outdoor levels. The exposure levels during cooking in rural kitchens were 140 μg/m³ (SD 116) in winter and 121 μg/m³ (SD 70) in summer, the highest in all microenvironments. Winter and summer values were 252 μg/m³ (SD 103) and 204 μg/m³ (SD 105), respectively, for rural people using biomass for fuel, much higher than those for rural people using LPG and electricity. By combining PM_2.5concentrations and time spent in different microenvironments, we found that 92% (winter) and 85% (summer) of personal exposure to PM_2.5in rural areas was attributable to indoor microenvironments, of which kitchens accounted for 24% and 27%, respectively. Consequently, more effective policies and measures are needed to replace biomass fuel with LPG or electricity, which would benefit the health of the rural population in China.     

Chemical characterization of indoor and outdoor fine particulate matter in an occupied apartment in Rome,Italy

The daily concentration and chemical composition of PM_2.5 was determined in indoor and outdoor 24‐h samples simultaneously collected for a total of 5 weeks during a winter and a summer period in an apartment sited in Rome, Italy. The use of a specifically developed very quiet sampler (<35 dB) allowed the execution of the study while the family living in the apartment led its normal life. The indoor concentration of PM_2.5 showed a small seasonal variation, while outdoor values were much higher during the winter study. Outdoor sources were found to contribute significantly to indoor PM concentration especially during the summer, when the apartment was naturally ventilated by opening the windows. During the winter the infiltration of outdoor PM components was lower and mostly regulated by the particle dimensions. Organics displayed In/Out ratios higher than unity during both periods; their indoor production increased significantly during the weekends, where the family stayed mostly at home. PM components were grouped into macrosources (soil, sea, secondary inorganics, traffic, organics). During the summer the main contributions to outdoor PM_2.5 came from soil (30%), secondary inorganics (29%) and organics (22%). Organics dominated both indoor PM_2.5 during the summer (60%) and outdoor and indoor PM_2.5 during the winter (51% and 66%, respectively).     

Factors influencing relationships between personal and ambient concentrations of gaseous and particulate pollutants

Previous exposure studies have shown considerable inter-subject variability in personal-ambient associations. This paper investigates exposure factors that may be responsible for inter-subject variability in these personal-ambient associations. The personal and ambient data used in this paper were collected as part of a personal exposure study conducted in Boston, MA, during 1999-2000. This study was one of a group of personal exposure panel studies funded by the U.S. Environmental Protection Agency's National Exposure Research Laboratory to address areas of exposure assessment warranting further study, particularly associations between personal exposures and ambient concentrations of particulate matter and gaseous co-pollutants. Twenty-four-hour integrated personal, home indoor, home outdoor and ambient sulfate, elemental carbon (EC), PM_2.5, ozone (O₃), nitrogen dioxide (NO₂) and sulfur dioxide were measured simultaneously each day. Fifteen homes in the Boston area were measured for 7 days during winter and summer. A previous paper explored the associations between personal-indoor, personal-outdoor, personal-ambient, indoor-outdoor, indoor-ambient and outdoor-ambient PM_2.5, sulfate and EC concentrations. For the current paper, factors that may affect personal exposures were investigated, while controlling for ambient concentrations. The data were analyzed using mixed effects regression models. Overall personal-ambient associations were strong for sulfate during winter (p < 0.0001) and summer (p < 0.0001) and PM_2.5 during summer (p < 0.0001). The personal-ambient mixed model slope for PM_2.5 during winter but was not significant at p = 0.10. Personal exposures to most pollutants, with the exception of NO₂, increased with ventilation and time spent outdoors. An opposite pattern was found for NO₂ likely due to gas stoves. Personal exposures to PM_2.5 and to traffic-related pollutants, EC and NO₂, were higher for those individuals living close to a major road. Both personal and indoor sulfate and PM_2.5 concentrations were higher for homes using humidifiers. The impact of outdoor sources on personal and indoor concentrations increased with ventilation, whereas an opposite effect was observed for the impact of indoor sources.