Particulate Pollution Episodes Research Articles

Impacts of urban expansion on meteorology and air quality in North China Plain during wintertime: A case study

The North China Plain (NCP) is one of the areas with a fast urbanization rate. The proportion of urban areas has increased from 1.78% in 2000 to 6.70% in 2015 in the NCP. Urban expansion induce variations in air pollutants are mainly determined by changes in meteorological conditions and atmospheric physicochemical processes. A persistent severe wintertime particulate pollution episode is simulated using the WRF-Chem model to investigate the impacts of land use/cover change on air quality in the NCP. Sensitivity simulations demonstrated that the urban expansion increases the near-surface temperature by approximately 0.2 °C, and further the development of the planetary boundary layer height by approximately 1.6%, but decreases the relative humidity by 0.4% on average. The near-surface O3 concentrations are increased by 2.2%, but the PM2.5 concentrations are decreased by 2.4% on average in the NCP. The near-surface concentration of NO2, SO2, and CO decrease by 4.5%, 2.2%, and 2.7%, respectively. The decrease in PM2.5 concentrations is approximately 8.9% in urban areas. Although urban expansion increases anthropogenic emissions of air pollutants, it alleviates particulate pollution to some degree, particularly in urban areas.

Heterogeneous HONO formation deteriorates the wintertime particulate pollution in the Guanzhong Basin, China

Despite implementation of strict emission mitigation measures since 2013, heavy haze with high levels of secondary aerosols still frequently engulfs the Guanzhong Basin (GZB), China, during wintertime, remarkably impairing visibility and potentially causing severe health issues. Although the observed low ozone (O3) concentrations do not facilitate the photochemical formation of secondary aerosols, the measured high nitrous acid (HONO) level provides an alternate pathway in the GZB. The impact of heterogeneous HONO sources on the wintertime particulate pollution and atmospheric oxidizing capability (AOC) is evaluated in the GZB. Simulations by the Weather Research and Forecast model coupled with Chemistry (WRF-Chem) reveal that the observed high levels of nitrate and secondary organic aerosols (SOA) are reproduced when both homogeneous and heterogeneous HONO sources are considered. The heterogeneous sources (HET-sources) contribute about 98% of the near-surface HONO concentration in the GZB, increasing the hydroxyl radical (OH) and O3 concentration by 39.4% and 22.0%, respectively. The average contribution of the HET-sources to SOA, nitrate, ammonium, and sulfate in the GZB is 35.6%, 20.6%, 12.1%, and 6.0% during the particulate pollution episode, respectively, enhancing the mass concentration of fine particulate matters (PM2.5) by around 12.2%. Our results suggest that decreasing HONO level or the AOC becomes an effective pathway to alleviate the wintertime particulate pollution in the GZB.

Nitrate debuts as a dominant contributor to particulate pollution in Beijing: Roles of enhanced atmospheric oxidizing capacity and decreased sulfur dioxide emission

Implementation of strict emission mitigation measures since 2013 has significantly changed air pollutants in the Beijing-Tianjin-Hebei region (BTH), China. Observations show that ozone (O3) concentrations have increased by 62.40% (27.84%) and SO2 concentrations have decreased by 56.42% (35.07%) during particulate pollution episodes in Beijing (BTH) in the autumn from 2013 to 2015. The measured nitrate concentration in Beijing has increased markedly, which to a large degree offsets the sulfate decrease caused by SO2 emission mitigation. Using the WRF-Chem model, we demonstrate that the enhanced nitrate formation is primarily attributed to increasing atmospheric oxidizing capacity (AOC) and decreasing sulfate competition for base ions. A 9.41–46.24% (7.58–40.97%) decrease in OH radical (O3) concentrations in October 2015 reduces nitrate and fine particulate matters (PM2.5) concentrations by 2.51–18.18% and 3.15–18.90% in Beijing, respectively. Based on the scenario in October 2015, if the SO2 emission increases by 20.00–100.00%, the PM2.5 concentration increases by 3.02–11.21%, but the nitrate level decreases by 2.48–21.87% simultaneously. Our results suggest that the nitrate aerosol has become a dominant contributor to particulate pollution in Beijing and that decreasing AOC is critical to mitigate nitrate and PM2.5 concentrations.

Strong regional transport of volatile organic compounds (VOCs) during wintertime in Shanghai megacity of China

Measurements of volatile organic compounds (VOCs) were performed as well as other pollutants in Shanghai in winter. The whole measurements were classified into three types of periods, including particulate pollution episodes (PPE), VOC pollution episodes (VPE), and relatively clean periods based on the pollution characteristics. Of these types, PPE have the highest fine particulate matter (PM2.5) mass concentrations and second-highest VOC concentrations, mainly impacted by the regional transport of aged air masses from the northwest. VPE generally concern long-lasting high concentrations of VOCs under stagnant atmospheric conditions due to the accumulation of local emissions. Five sources of VOCs were identified by the positive matrix factorization (PMF) model, and furthermore, the analysis of VOCs concentration weighted trajectory (CWT) was employed to investigate the potential source region and even to validate the source identification to some extent. As a result, VOCs in Shanghai in winter were mainly from solvent usage (23.9%), vehicle emissions mixed with some petrochemical emissions (24.7%), natural gas and background (23.6%), combustion-related to regional transport (22.1%), and secondary formation (5.7%). The regional transport, usually with large combustion sources, played more important roles (41.9%) in VOCs during PPE compared to VPE and clean periods. The contribution of local emissions like vehicle exhaust and petrochemical emissions increased during VPE compared to PPE and clean periods. Clean periods have low PM2.5 and low VOC concentrations, with a large contribution from the regional background. The present study highlighted the regional transport of VOCs should be taken into account for policymakers when making the city scale controlling measures.

Characteristics of air pollution episodes influenced by biomass burning pollution in Shanghai, China

Abstract In the atmosphere, biomass burning can interact with other pollution sources and thereby aggravate air pollution. However, its influences on the occurrence and development of air pollution remain poorly understood. In this study, the characteristics of air pollution episodes influenced by biomass burning was investigated based on the field observation in Shanghai from 2014 to 2016. Results indicated that the fine particle pollution was serious during the whole observation period, and the high particulate pollution episodes mostly occurred in winter and spring. Four studied cases indicated that the ways to initiate high air pollution episodes were diverse, including local pollution sources, external transport and combined interaction of multiple pollution sources. All four high air pollution episodes behaved high K+, CO and NH3 concentrations, showing the existence of biomass burning pollution. And most of biomass burning pollution were from northwest China and some provinces in east and southeast China, which had active biomass burning activities. In the high pollution episodes, secondary inorganic aerosols (SIA) accounted for a large proportion of PM2.5, but SIA did not always initiate high pollution episodes. The high concentrations of sulfate and nitrate aerosols brought by the transport of biomass burning could also induce the occurrence of high pollution episodes. Also, the mixing of biomass burning plumes with other pollution sources could enhance SIA formation and aggravate air pollution. This study highlights the significant roles of biomass burning in the occurrence and development of high air pollution.

Chemical Characteristics and Sources of Volatile Organic Compounds in Shanghai During an Ozone and Particulate Pollution Episode in May 2019

In the urban area of Shanghai during the complex pollution episode, ozone and PM2.5 were continuously measured from May 1 to May 28, 2019. The characterization of volatile organic compounds (VOCs) and their relationship with secondary formation were studied. The results show that in May 2019, there were four different ozone and PM2.5 pollution processes in Shanghai. The combined pollution of PM2.5 and ozone that occurred under the meteorological conditions of average temperature of approximately 26℃ and relative humidity of approximately 40% was analyzed. The photochemical consumption of VOCs was significantly positively correlated with the maximum net growth of O3 and there was a significant positive correlation between SOAP and PM2.5. The key reactive species of VOCs that significantly contribute to ozone generation were m,p-xylene, ethylene, toluene, propylene, and o-xylene. The key reactive species that significantly contribute to secondary organic aerosols (SOA) were toluene, m,p-xylene, ethylbenzene, o-xylene, and 1,2,3-trimethylbenzene.

Satellite-derived spatiotemporal PM2.5 concentrations and variations from 2006 to 2017 in China

The PM2.5 concentration is an important evaluation index for the global Sustainable Development Goals (SDGs) for its negative impacts on human health. Last decade, several fine particulate pollution episodes occurred in the vast area of China. In response to this, the Chinese government has stepped up efforts to tackle air pollution. In this paper, the temporal trends of PM2.5 and the quantitative potential impact of environmental governance on PM2.5 are analyzed for China. Due to the lack of historical records, a two-stage model was used to estimate the historical PM2.5 concentrations, combined with the newly released satellite-based aerosol optical depth (AOD) product (MODIS Collection 6.1) and other data. The estimated PM2.5 concentrations showed strong consistency with the surface observations. Furthermore, significant seasonal variations existed in the PM2.5 concentrations and the temporal trends were captured, especially in city clusters. Then eight major city clusters were selected as typical samples. All the city clusters showed decrease trends in recent years, with PM2.5 concentrations in these regions decreased by 0.269–1.604 μg m−3 year−1. From 2006 to 2017, the annual PM2.5 concentrations decreased by 7.83%–26.35% in the major city clusters among China. Technological innovation and environmental governance play an important role in the decrease of PM2.5. In order to quantify the influence of governance, environmental regulation intensity and synergy were applied as the indicators of the internal governance and co-governance in each city cluster. In most city clusters, PM2.5 concentrations were significantly negatively correlated with regional internal governance and co-governance (R = −0.596 to −0.930, p < 0.05), and the effect on PM2.5 lasted for several years. However, 1- to 2-year lagged effect was found for governance, which means that the regulatory measures should be enhanced to decrease PM2.5 in the future to achieve the SDGs in China.

Characteristics of Speciated Atmospheric Mercury in Chongming Island, Shanghai

Continuous monitoring of gaseous elemental mercury (GEM), reactive gaseous mercury (RGM) and particulate mercury (PBM) was conducted in the Dongtan wetland park in Chongming Island, Shanghai from March 2014 to February 2015. The average concentrations of GEM, RGM, and PBM were (2.75±1.13) ng·m-3, (13.39±15.95) pg·m-3, and (21.89±40.42) pg·m-3, respectively, higher than the background concentrations of Northern Hemisphere. The atmospheric mercury showed obvious seasonal variations, with the highest seasonal average GEM concentration in summer (3.65 ng·m-3), which was mainly influenced by natural sources, while lower GEM concentrations appeared in autumn and winter influenced mainly by anthropogenic sources. The concentration of RGM was highest in spring and lowest in winter, mainly influenced by the wind direction, while PBM showed higher concentrations in autumn and winter, when heavy fine particulate pollution episodes occurred frequently. The concentrations of GEM and PBM were generally elevated in nighttime and lower in daytime caused by the mixing condition of the air masses. Most of the high RGM concentration values occurred in the afternoon of all seasons due to the higher atmospheric oxidation. The concentrations of GEM and PBM were higher in the west wind due to the emission from anthropogenic sources in Shanghai, Jiangsu, etc. The RGM concentration in southeast wind was obviously higher than those in other wind directions. The RGM was mainly from the anthropogenic sources, and the smaller wind in the southeast direction was against the dispersion of RGM.

Process Contributions to Secondary Inorganic Aerosols during Typical Pollution Episodes over the Pearl River Delta Region, China

The Integrated Process Rate (IPR) analysis embedded in CAMx model was used to quantify contributions from different atmospheric processes to the formations and accumulations of ambient PM_(2.5) and the secondary inorganic aerosol (SIA) during two typical particulate pollution episodes in different seasons in the Pearl River Delta (PRD) region. Process analysis results indicated that primary fine particle emissions were the major sources of high ambient PM_(2.5) in urban areas with intensive anthropogenic activities. Aerosol process and advection transport were another two major processes contributing to the increasing PM_(2.5) and SIA over the PRD region. Regarding formation of SIA species, elevations of nitrate and ammonium at Guangzhou (urban), Heshan (rural) and Panyu (suburban) sites were largely associated with aerosol process, while those at Huizhou (urban) site were dominated by advection process, but elevated sulfate concentrations at these four sites were all dominated by advection process. The difference can be attributed to spatial variations of SO_2, NO_x and NH_3 emissions, site locations and meteorological conditions. Advection, aerosol chemistry, deposition and vertical diffusion were important pathways to remove SIA at these four sites. Within the hours with most growing PM_(2.5) concentrations, aerosol process was the most important contributor to the formation of new SIA throughout the entire planetary boundary layer.

Averaging period effects on the turbulent flux and transport efficiency during haze pollution in Beijing, China

Based on observations at the heights of 140 and 280 m on the Beijing 325-m meteorological tower, this study presents an assessment of the averaging period effects on eddy-covariance measurements of the momentum/scalar flux and transport efficiency during wintertime haze pollution. The study period, namely from January 6 to February 28 2013, is divided into different episodes of particulate pollution, as featured by varied amounts of the turbulent exchange and conditions of the atmospheric stability. Overall, turbulent fluxes of the momentum and scalars (heat, water vapor, and CO2) increase with the averaging period, namely from 5, 15, and 30 up to 60 min, an outcome most evident during the ‘transient’ episodes (each lasting for 2–3 days, i.e., preceded and followed by clean-air days with mean concentrations of PM1 less than 40 μg m−3). The conventional choice of 30 min is deemed to be appropriate for calculating the momentum flux and its transport efficiency. By comparison, scalar fluxes and their transport efficiencies appear more sensitive to the choice of an averaging period, particularly at the upper level (i.e., 280 m). It is presupposed that, for urban environments, calculating the momentum and scalar fluxes could invoke separate averaging periods, rather than relying on a single prescription (e.g., 30 min). Furthermore, certain characteristics of urban turbulence are found less sensitive to the choice of an averaging period, such as the relationship between the heat-to-momentum transport efficiency and the local stability parameter.

Biomass burning contribution to ambient air particulate levels at Navrongo in the Savannah zone of Ghana

The concentrations of airborne particulate matter (PM) in Navrongo, a town in the Sahel Savannah Zone of Ghana, have been measured and the major sources have been identified. This area is prone to frequent particulate pollution episodes due to Harmattan dust and biomass burning, mostly from annual bushfires. The contribution of combustion emissions, particularly from biomass and fossil fuel, to ambient air particulate loadings was assessed. Sampling was conducted from February 2009 to February 2010 in Navrongo. Two Gent samplers were equipped to collect PM10 in two size fractions, coarse (PM10-2.5) and fine (PM2.5). Coarse particles are collected on a coated, 8-μm-pore Nuclepore filter. Fine particle samples were sampled with 47-mm-diameter Nuclepore and quartz filters. Elemental carbon (EC) and organic carbon (OC) concentrations were determined from the quartz filters using thermal optical reflectance (IMPROVE/TOR) methods. Elements were measured on the fine-particle Nuclepore filters using energy-dispersive x-ray fluorescence. The average PM2.5 mass concentration obtained at Navrongo was 32.3 μg/m3. High carbonaceous concentrations were obtained from November to March, the period of Harmattan dust and severe bush fires. Total carbon was found to contribute approximately 40% of the PM2.5 particulate mass. Positive matrix factorization (PMF) suggested six major sources contributing to the PM2.5 mass. They are two stroke engines, gasoline emissions, soil dust, diesel emissions, biomass burning, and resuspended soil dust. Biomass combustion (16.0%) was identified as second most important source next to soil dust at Navrongo. Implications: Black carbon has now been recognized as playing a major role in radiation forcing, and one major source of biomass burning is slash-and-burn agriculture. Such practices are used in Sub-Saharan Africa and the time for field burning corresponds to the time when there is also substantial transport of Saharan dust to West Africa. This paper shows the major role of biomass burning on fine particle concentrations in northern Ghana and provides useful data on the EC concentrations in this area.

Exacerbations d’asthme en Guadeloupe et éruption volcanique à Montserrat (70 km de la Guadeloupe)

This study evaluates the impact of the ash cloud emitted in February 2010 during the eruption of the Soufrière Hill volcano of the island of Montserrat (70 km from Guadeloupe), on asthma exacerbations registered by the emergency hospital services in the archipelago of Guadeloupe in February 2010. We first recorded the clinical features and outcome of each adult patient admitted as an emergency with an acute asthma exacerbation during this period, then compared the admission rates for asthma exacerbation, concentrations of particulates and chemical pollutants, and climatic parameters before, during, and after exposure to the ash cloud. Then, using a generalized linear model defined by a Poisson regression, we calculated the risks related to these factors. There was an increase in acute asthma admissions during and after exposure to the ash cloud (2.44/day versus 5.6/day, P<0.003). PM10 (particles<10 microns) were the major particulate pollution episodes (mean: 223 μg/m(3)). Asthmatics admitted acutely during the period of pollution were young adults (35 [18-49] years old), and the majority had asthma classified as intermittent (57%, n=27). In multivariate analysis, PM10 were a risk factor for acute asthma presentations during this period (aRR 2.89, 95% [from 1.69 to 4.93]). This study describes the clinical data and outcome of adult patients admitted to emergency asthma exacerbation during the eruption of the Soufrière Hills Volcano in Montserrat and indicates that there was a significant impact of the ash plume on respiratory health, mainly in patients with intermittent asthma.

Wintertime particulate pollution episodes in an urban valley of the Western US: a case study

Abstract. This study investigates the causes of elevated PM2.5 episodes and potential exceedences of the US National Ambient Air Quality Standards (NAAQS) in Truckee Meadows, Nevada, an urban valley of the Western US, during winter 2009/2010, an unusually cold and snowy winter. Continuous PM2.5 mass and time-integrated chemical speciation data were acquired from a central valley monitoring site, along with meteorological measurements from nearby sites. All nine days with PM2.5 &gt; 35 μg m−3 showed 24-h average temperature inversion of 1.5–4.5 °C and snow cover of 8–18 cm. Stagnant atmospheric conditions limited wind ventilation while highly reflective snow cover reduced daytime surface heating creating persistent inversion. Elevated ammonium nitrate (NH4NO3) and water associated with it are found to be main reasons for the PM2.5 exceedances. An effective-variance chemical mass balance (EV-CMB) receptor model using locally-derived geological profiles and inorganic/organic markers confirmed secondary NH4NO3 (27–37%), residential wood combustion (RWC; 11–51%), and diesel engine exhaust (7–22%) as the dominant PM2.5 contributors. Paved road dust and de-icing materials were minor, but detectable contributors. RWC is a more important source than diesel for organic carbon (OC), but vice versa for elemental carbon (EC). A majority of secondary NH4NO3 is also attributed to RWC and diesel engines (including snow removal equipment) through oxides of nitrogen (NOx) emissions from these sources. Findings from this study may apply to similar situations experienced by other urban valleys.

The representation of dust transport and missing urban sources as major issues for the simulation of PM episodes in a Mediterranean area

Abstract. Due to its adverse effects on human health, atmospheric particulate matter (PM) constitutes a growing challenge for air quality management. It is also a complex subject of study. The understanding of its atmospheric evolution is indeed made difficult by the wide number of sources and the numerous processes that govern its evolution in the troposphere. As a consequence, the representation of particulate matter in chemistry-transport models needs to be permanently evaluated and enhanced in order to refine our comprehension of PM pollution events and to propose consistent environmental policies. The study presented here focuses on two successive summer particulate pollution episodes that occurred on the French Mediterranean coast. We identify and analyze the constitutive elements of the first and more massive episode and we discuss their representation within a eulerian model. The results show that the model fails in reproducing the variability and the amplitude of dust import from western Africa, and that it constitutes a strong bias in PM daily forecasts. We then focus on the lack of diurnal variability in the model, which is attributed to missing urban sources in standard emission inventories, and notably the resuspension of particles by urban road traffic. Through a sensitivity study based on PM and NOx measurements, we assess the sensitivity of PM to local emissions and the need to reconsider road traffic PM sources. In parallel, by coupling the CHIMERE-DUST model outputs to our simulation, we show that the representation of transcontinental dust transport allows a much better representation of atmospheric particles in southern France, and that it is needed in the frame of air quality management for the quantification of the anthropogenic part of particulate matter pollution.

Long-term assessment of particulate matter using CHIMERE model

Particulate matter (PM) and aerosols have became a critical pollutant and object of several research applications, due to their increasing levels, especially in urban areas, causing air pollution problems and thus effects on human health. The main purpose of this study is to perform a first long-term air quality assessment for Portugal, regarding aerosols and PM pollution. The CHIMERE chemistry-transport model, forced by the MM5 meteorological fields, was applied over Portugal for 2001 year, with 10 km horizontal resolution, using an emission inventory obtained from a spatial top-down disaggregation of the 2001 national inventory database. The evaluation model exercise shows a model trend to overestimate particulate pollution episodes (peaks) at urban sites, especially in winter season. This could be due to an underprediction of the winter model vertical mixing and also to an overestimation of PM emissions. Simulated inorganic components (ammonium and sulfate) and secondary organic aerosols (SOA) were compared to measurements taken at Aveiro (northwest coast of Portugal). An underestimation of the three components was verified. However, the model is able to predict their seasonal variation. Nevertheless, as a first approach, and despite the complex topography and coastal location of Portugal affected by sea salt natural aerosols emissions, the results obtained show that the model reproduces the PM levels, temporal evolution, and spatial patterns. The concentration maps reveal that the areas with high PM values are covered by the air quality monitoring network.

Source identification of PM 2.5 in an arid Northwest U.S. City by positive matrix factorization

Spokane, WA is prone to frequent particulate pollution episodes due to dust storms, biomass burning, and periods of stagnant meteorological conditions. Spokane is the location of a long-term study examining the association between health effects and chemical or physical constituents of particulate pollution. Positive matrix factorization (PMF) was used to deduce the sources of PM 2.5 (particulate matter ≤2.5 μm in aerodynamic diameter) at a residential site in Spokane from 1995 through 1997. A total of 16 elements in 945 daily PM 2.5 samples were measured. The PMF results indicated that seven sources independently contribute to the observed PM 2.5 mass: vegetative burning (44%), sulfate aerosol (19%), motor vehicle (11%), nitrate aerosol (9%), airborne soil (9%), chlorine-rich source (6%) and metal processing (3%). Conditional probability functions were computed using surface wind data and the PMF deduced mass contributions from each source and were used to identify local point sources. Concurrently measured carbon monoxide and nitrogen oxides were correlated with the PM 2.5 from both motor vehicles and vegetative burning.

Dispersion modelling of a wintertime particulate pollution episode in Christchurch, New Zealand

This paper examines the inter-suburb dispersion of particulate air pollution in Christchurch, New Zealand, during a wintertime particulate pollution episode. The dispersion is simulated using the RAMS/CALMET/CALPUFF modelling system, with data from a detailed emissions inventory of home heating, motor vehicles and industry. During the period 27 July–1 August 1995, peak 1 h and 24 h PM 10 concentrations of 368 and 107 μg m −3, respectively, were observed. Peak concentrations occurred at night, when particulate emissions from wood- and coal-burning domestic heating appliances were at a maximum and emitted into a stable boundary layer. The model is generally able to reproduce the observed PM 10 time series recorded at surface monitors located throughout the urban area. For this simulation, the fractional gross error ranges between 0.69 and 0.99, and the fractional bias ranges between −0.17 and 0.30. Strong horizontal concentration gradients of 100 μg m −3 km −1, both in the observational record and model predictions, are apparent. Three emission reduction options, designed to reduce the severity of particulate pollution episodes in Christchurch, are simulated. When both domestic open-hearth fires and all coal burning are removed, the 24 h average peak concentration is reduced by 55%. The number of guideline exceedences of PM 10 in the modelled period is reduced from five to one. Removing open-hearth fires results in 42% reduction in PM 10 concentration, resulting in three exceedences of the guideline, and removing coal-burning fires yields a 32% reduction in PM 10, resulting in four exceedences of the guideline.

Alteration in Lung Particle Translocation, Macrophage Function, and Microfilament Arrangement in Monocrotaline-Treated Rats

Individuals with preexisting cardiopulmonary disease are thought to be more susceptible to acute episodes of particulate pollution resulting in increased morbidity and mortality. Our study was designed to evaluate particle fate and macrophage function in an animal model of monocrotaline (MCT)-induced pulmonary hypertension. Two weeks following a single MCT injection, Sprague–Dawley rats were exposed sequentially to two different colored fluorescent microspheres 1.0 μm in diameter by aerosolization. Morphometric evaluation of lung sections was performed 0 and 24 h following the final particle exposure to determine the intrapulmonary location of inhaled microspheres. A decrease in the number of particles phagocytized by alveolar macrophages and an increase of free particles overlying the epithelium were found in MCT-treated animals compared with control. Pulmonary macrophages recovered by bronchoalveolar lavage were evaluated for chemotactic and phagocytic ability. Macrophage chemotaxis was significantly impaired following MCT treatment compared with controls, whereas phagocytic activity of macrophages lavaged from MCT and control treatment groups was similar. Macrophages were stained for filamentous (F) and globular (G) actin using Texas-Red-labeled phalloidin and Oregon-green-labeled DNase I, respectively. The area of microfilament staining for F and G actin increased, but the ratio of F/G actin was significantly decreased in animals with MCT treatment compared with control. While the responses observed with MCT treatment, such as pulmonary edema, polymorphonuclear leukocytes influx, and unique macrophage morphology may contribute to impaired macrophage function, the change in microfilament arrangement suggests that MCT may inhibit macrophage chemotaxis and impair particle clearance from the lungs.