Measurements of indoor radon concentrations in the Santiago de Compostela area

Galician soils are among those with the highest (222)Rn exhalation rates in Spain. A year-round study of the indoor (222)Rn concentration in buildings in the Santiago de Compostela area (Galicia, Northwest of Spain) was performed. The study is based on systematic samplings with active charcoal canisters, following a modified EPA 520/5-87-005 protocol. These measurements were complemented by others obtained using etched track dosimeters. Each data set follows a log-normal distribution, with a geometric mean of (253+/-3)Bqm(-3) for charcoal canisters and (285+/-2.5)Bqm(-3) for etched track detectors. After correcting for the different measuring conditions, the mean value of both methods differed by only 2%. A careful analysis of the seasonal dependence of our measurements did not reveal any significant seasonal variations in the (222)Rn concentration. Parallel to these measurements, different meteorological parameters were recorded, which revealed a direct correlation between the indoor radon concentration and the outdoor temperature derivative with respect to time.     

Indoor radon levels: Effects of energy-efficiency in homes

The expectation of elevated ²²²Rn levels in modern homes that have low air interchange rates with the outdoor air caused us to survey both solar and conventional homes in northeastern New York State. As a group, homes that are more airtight have three times the ²²²Rn levels of the conventional homes; they have other specific problems that are introduced or exaggerated by modern construction. For example, the highest two levels of radon in the solar homes give doses over 30 years that are known to produce lung cancer in 1% of uranium miners. Summer readings in more than one-half of the cases are different from winter ones by a factor of two or more, so that year-round measurements are necessary for precise dosimetry. The track-etching technique is ideally suited for such measurements. Radon emanation measurements on soils and sand demonstrate a considerable variety of release rates.     

Time-integrating radon gas measurements in domestic premises: comparison of short-, medium- and long-term exposures

To identify the most applicable technology for the short-term assessment of domestic radon levels, comparative assessments of a number of integrating detector types, including track-etch, electret and activated charcoal were undertaken. Thirty-four unremediated dwellings in a high-radon area were monitored using track-etch detectors exposed for one-month and three-month periods. In parallel, one-week measurements were made in the same homes at one-month intervals, using co-located track-etch, charcoal and electret detectors exposed simultaneously, while three of the homes were also monitored by continuous-sampling detectors at hourly intervals over extended periods. Calibration of dose-integrating devices against each other and against continuous-monitoring systems confirmed good responsivity and linearity. Although track-etch, charcoal and electret devices are suitable in principle for one-week measurements, zero-exposure offset and natural radon variability cause many one-week results to be equivocal, necessitating repetition of the measurement. One-week exposures can be reliable indicators in low-radon areas or for new properties, but in high-radon areas, the use of three-month exposures is indicated. This analysis also established confidence limits for short-term measurements.     

Human exposure to polybrominated diphenyl ethers (PBDE), as evidenced by data from a duplicate diet study, indoor air, house dust, and biomonitoring in Germany

Polybrominated diphenyl ethers (PBDE) are used as flame retardants in a wide variety of products. As part of the Integrated Exposure Assessment Survey (INES), this study aimed to characterize the exposure of an adult German population using duplicate diet samples, which were collected daily over seven consecutive days, and indoor air and house dust measurements. Our study population consisted of 27 female and 23 male healthy subjects, aged 14–60 years, all of whom resided in 34 homes in southern Bavaria. In these 34 residences the air was sampled using glass fiber filters and polyurethane foams and the dust was collected from used vacuum cleaner bags.The median (95th percentile) daily dietary intake of six Tetra- to HeptaBDE congeners was 1.2 ng/kg b.w. (3.3 ng/kg b.w.) or 67.8 ng/day (208 ng/day) (calculated from the 7-day median values of each study subject). Concentrations in indoor air and dust (cumulative Tri- to DecaBDE congener readings) ranged from 8.2 to 477 pg/m³ (median: 37.8 pg/m³) and 36.6 to 1580 ng/g (median: 386 ng/g), respectively. For some congeners, we identified a significant correlation between air and dust levels.The median (95th percentile) blood concentration of total Tetra- to HexaBDE congener readings was 5.6 (13.2) ng/g lipid. No significant sex differences were observed, but higher blood concentrations were found in younger participants. Using a simplified toxicokinetic model to predict the body burden from exposure doses led to results that were of the same order of magnitude as the measured blood concentrations.Based on these measurements and given our exposure assumptions, we estimated for the total tetra- to heptabrominated congener count an average (high) comprehensive total daily intake of 1.2 ng/kg b.w. (2.5 ng/kg b.w.). Overall, our results suggest that dietary exposure is the dominant intake pathway at least in our study population, responsible for 97% (average intake) and 95% (high intake) of the total intake of an adult population.     

Rn concentration in public secondary schools in Galicia (Spain)

In the framework of a ²²²Rn screening campaign that was carried out in 58 public secondary schools in Galicia (NW Spain), the largest radon-prone area in the Iberian Peninsula, a positive correlation between indoor ²²²Rn concentration and outdoor gamma exposure rate was obtained. A new approach to the data acquisition in screening surveys was tested, improving the performances of this type of study and gathering useful data for future remedial actions. Using short-period detectors (charcoal canisters) firstly, in order to detect places showing ²²²Rn concentrations over 400 Bq m⁻³, the number of locations to be measured with long-period detectors (etched track detectors) is reduced. In this screening campaign, 34% of the schools surveyed presented at least one site exceeding the 400 Bq m⁻³ recommended action level established by the EU, and 15% had at least one site with ²²²Rn values over 800 Bq m⁻³. The maximum value recorded was 2084 ± 63 Bq m⁻³. These results are discussed and compared with data obtained in schools of several countries with similar geology. Seven schools were also studied for seasonal variations of ²²²Rn activity concentration. The results were not conclusive, and no significant correlation between season and ²²²Rn concentration was established. Finally, a continuous ²²²Rn concentration monitor was placed in the secondary school exhibiting a mean value of the ²²²Rn concentration very close to 400 Bq m⁻³. Maximum ²²²Rn concentration values were found to occur at times when the school was unoccupied.     

基于面板数据的研发投入对区域经济增长影响分析

利用长江经济带110个地市1990~2013年RD投入与经济增长水平的相关面板数据,通过单位根检验、协整性检验和面板数据模型,对RD经费投入和人员投入与区域经济增长的影响进行了分析。结果表明:1长江经济带各市的经济增长与RD投入存在长期稳定的关系,RD短期投入对区域经济增长的影响则存在着一定的滞后效应;2RD人员投入产出弹性高于RD经费投入,说明区域经济增长对RD人员的依赖性更大;3RD投入表现出东部地区高于中部地区,中部地区高于西部地区,但RD投入对区域经济增长的影响则表现出中西部大于东部的现象,造成这一现象的原因在于所处发展阶段的不同和东中西区域经济特征不同。最后,从加大RD经费投入强度、制定RD投入中长期计划等方面提出了促进区域经济增长的建议。     

Determination of aniline and related mono-aromatic amines in indoor air in selected Canadian residences by a modified thermal desorption GC/MS method

A modified thermal desorption method to determine low levels of aniline and other related mono-aromatic amines (MAAs) in residential air is described. The method was successfully applied to the determination of levels of these chemicals in residential air from 69 selected homes in two Canadian regions. Instrument detection limits of between 0.02 and 0.06 ng per thermal desorption tube were achieved for aniline and other MAAs. In the absence of environmental tobacco smoke (ETS) the mean concentrations of aniline in both indoor air and outdoor air were similar, at about 0.01 microgram/m3 after correction with field blanks. There was however a statistically significant difference in aniline concentrations between field blanks and indoor or outdoor air samples. No significant difference of aniline levels in the two study regions was observed. A clear link between aniline concentrations in indoor air and smoking activities inside homes was evident. Analysis of cigarette leaves indicated that aniline was most likely formed due to combustion during smoking. Shoe polishing was identified as another source of aniline in indoor air.     

Radon-222 in Brazil: an outline of indoor and outdoor measurements

This study discusses the methodology for measuring and assessing the radon concentration in indoor and outdoor environments. A research study was developed to investigate the long-term behavior of the diurnal and seasonal fluctuations of radon (222)Rn EEC (Equilibrium-Equivalent Concentration) and the influence of temperature and other climatic aspects on this behavior. The study was performed by means of both integrated and instantaneous measurements of radon and its short-lived daughter products for a period of 1 year in an indoor environment in Rio de Janeiro city, Brazil (reference environment), with continuous measurement, using a radon monitor with an alpha spectrometry detector.For a single day, a variability of about 50% could be observed in the (222)Rn EEC values measured on a hourly basis, with a maximum occurring early in the morning and a minimum in the afternoon. For the long-term period, seasonality is responsible for a two order of magnitude variability, with a maximum of 50 Bq.m(-3) in winter (dry season) and a minimum of 0.5 Bq.m(-3) in the summer months (wet season), outdoors. A negative correlation with temperature was observed. The conclusions of this experiment led to a survey of radon gas concentration in dwellings in Rio de Janeiro city, Brazil, in urban area with nearly 7 million inhabitants, through integrated sampling methods, using a Solid State Nuclear Track Detectors Technique (SSNTD). The study was conducted in different geomorphological locations in town. The radon gas concentration in Rio de Janeiro dwellings ranged from 5 Bq.m(-3) to 200 Bq.m(-3). A good correlation between indoor radon gas concentration and location of dwellings was observed. The seashore areas presented the lowest levels of indoor radon concentration, whereas the highest levels were found close to the mountains.     

近34年祁连山南坡植被覆盖变化与气象因子关系研究

基于1982~2015年GIMMS NDVI数据，通过趋势线法和相关性分析方法，对祁连山南坡植被覆盖变化及影响因素进行分析。研究结果表明：（1）祁连山南坡植被覆盖整体呈显著上升趋势，线性回归增速为0.99%/10 a；各季节平均NDVI依次为夏季>秋季>春季>冬季， NDVI变化斜率排序依次为冬季>夏季>秋季>春季； NDVI月变化趋势基本一致，夏季NDVI在2004~2015年最大。（2）近34年来，祁连山南坡大部分区域属于常绿区域，三时间阶段植被增加面积整体表现出增加-减少-增加趋势，且在2004~2015年之间植被增加面积最大，占比为92.66%，增加速度最快的区域在门源县境内。（3）在影响因素方面，研究区NDVI与气温的相关性（0.58）大于降雨的相关性（0.27），研究区生长季 (4~9月)植被覆盖受气温和降水共同影响。     

Indoor radon concentration in geothermal areas of central Italy

The indoor radon (²²²Rn) activity concentration was measured between January and June in the schools of two geothermal areas in Tuscany, central Italy. One of these areas (the Larderello area) is characterized by a large number of geothermal power plants, covering about 9% of the world’s geothermal power production. In contrast, the other area, Monte Pisano, has not any such facilities. About 250 measurements were made using track etch detectors. Only a slight difference in the concentrations between the two major sampling areas (98 Bq m⁻³ for Larderello area and 43 Bq m⁻³ for Monte Pisano area) was found, and this was related to different geological characteristics of the ground and not the presence of the geothermal plants. The measured radon concentrations were always well below the intervention levels in both areas, and health risks for students and personnel in the examined schools were excluded.     

东洞庭湖水面面积变化监测及其与水位的关系

开展东洞庭湖水面面积长时间变化监测研究对于湖区洪涝旱灾监测、灾害评估等具有重要意义。采用2000~2017年的经过辐射一致性校正的Landsat Collection 1遥感数据集,在ENVI遥感数据处理平台下采用4种常见的水体提取方法（单波段阈值、多波段谱间关系、水体指数、支持向量机）开展了水面面积遥感提取方法比较及东洞庭湖区长时间序列水面面积提取,以此数据为基础开展了东洞庭湖区近18年来湖区水面面积年内和年际变化研究,并探讨了水面面积与城陵矶水文站水位之间的相关关系。结果显示：Landsat Collection 1遥感数据集具有较高的空间和时间分辨率,可以满足东洞庭区长时间序列水面面积提取,且水面面积提取精度较好;采用支持向量机方法提取的湖区多年水面面积平均值为569.9 km2,丰水期水面范围波动较大,而枯水期变化较小;湖区水面面积变化与城陵矶水位变化存在紧密相关关系,不管线性模型还是多项式模型均能准确地描述两者变化关系,受湖区地形分布特征影响,水面面积与水位之间的关系在丰水期较紧密,而枯水期两者之间的相关关系明显降低。     

血吸虫病疫情与地理环境因子的多元相关分析

探索鄱阳湖血吸虫病典型疫区的社会、经济、环境因子与血吸虫病疫情的相互关系及其相关程度。采用经典统计学中单相关、偏相关和复相关系数研究南昌县43个行政村血吸虫病感染人数与疫水接触指数、耕牛存栏数、行政村水域面积、行政村湖边边界长度和行政村到鄱阳湖边界的距离的内在联系和相互关系。所选5个因子与感染人数的简单相关系数都达到了005置信水平,固定疫水分布各因子计算疫水接触各因子与“感染人数”的偏相关系数,与固定疫水接触各因子计算疫水分布各因子与“感染人数”的偏相关系数,都小于简单相关系数,说明疫水分布因子与疫水接触因子具有内在关联;“感染人数”与所有5个因子的复相关系数为0.948,达到了0.005的极显著置信水平。所选的村级宏观因子都与血吸虫病疫情显著相关     

Higher energy efficient homes are associated with increased risk of doctor diagnosed asthma in a UK subpopulation

IntroductionThe United Kingdom (UK) has one of the highest prevalence of asthma in the world, which represents a significant economic and societal burden. Reduced ventilation resulting from increased energy efficiency measures acts as a modifier for mould contamination and risk of allergic diseases. To our knowledge no previous study has combined detailed asset management property and health data together to assess the impact of household energy efficiency (using the UK Government's Standard Assessment Procedure) on asthma outcomes in an adult population residing in social housing.MethodsPostal questionnaires were sent to 3867 social housing properties to collect demographic, health and environmental information on all occupants. Detailed property data, residency periods, indices of multiple deprivation (IMD) and household energy efficiency ratings were also investigated. Logistic regression was used to calculate odds ratios and confidence intervals while allowing for clustering of individuals coming from the same location.ResultsEighteen percent of our target social housing population were recruited into our study. Adults had a mean age of 59 (SD ± 17.3) years and there was a higher percentage of female (59%) and single occupancy (58%) respondents. Housing demographic characteristics were representative of the target homes. A unit increase in household Standard Assessment Procedure (SAP) rating was associated with a 2% increased risk of current asthma, with the greatest risk in homes with SAP > 71. We assessed exposure to mould and found that the presence of a mouldy/musty odour was associated with a two-fold increased risk of asthma (OR 2.2 95%; CI 1.3–3.8). A unit increase in SAP led to a 4–5% reduction in the risk of visible mould growth and a mouldy/musty odour.DiscussionIn contrast to previous research, we report that residing in energy efficient homes may increase the risk of adult asthma. We report that mould contamination increased the risk of asthma, which is in agreement with existing knowledge. Exposure to mould contamination could not fully explain the association between increased energy efficiency and asthma. Our findings may be explained by increased energy efficiency combined with the provision of inadequate heating, ventilation, and increased concentrations of other biological, chemical and physical contaminants. This is likely to be modified by a complex interaction between occupant behaviours and changes to the built environment. Our findings may also be confounded by our response rate, demographic and behavioural differences between those residing in low versus high energy efficient homes, and use of self-reported exposures and outcomes.ConclusionEnergy efficiency may increase the risk of current adult asthma in a population residing in social housing. This association was not significantly modified by the presence of visible mould growth, although further research is needed to investigate the interaction between other demographic and housing characteristic risk factors, especially the impact of fuel poverty on indoor exposures and health outcomes.Study implicationsA multidisciplinary approach is required to assess the interaction between energy efficiency measures and fuel poverty behaviours on health outcomes prior to the delivery of physical interventions aimed at improving the built environment. Policy incentives are required to address fuel poverty issues alongside measures to achieve SAP ratings of 71 or greater, which must be delivered with the provision of adequate heating and ventilation strategies to minimise indoor dampness. Changes in the built environment without changes in behaviour of domicile residents may lead to negative health outcomes.     

A study of radon levels in NHS premises in affected areas around the UK

Radon gas contributes a significant fraction of the natural background radiation dose, and in some areas raised levels are found in buildings. both homes and the workplace. Different UK Action Levels apply to homes and the workplace. because of the diurnal variation of radon. This study reviews the results for a number of hospitals throughout England and Wales. and suggests that the likelihood of finding raised radon levels is similar in the workplace and homes in the same area. Radon measurements and consequent remediation of any raised levels are appropriate in all workplaces in radon Affected Areas with over 5% of houses above the UK domestic Action Level of 200 Bq m(-3).     

Analysis of urban heat island effect in Visakhapatnam,India, using multi-temporal satellite imagery: causes and possible remedies

The thermal data sets of Landsat for the years 2014 and 2019 are used to assess the transients of land surface temperature (LST) in Visakhapatnam, India. The variation in estimated temperature fields is compared with the land use pattern to validate temperature with reference to land use land cover (LULC). During the considered period, the built-up area in the study region increased by 63%. The aerial extent of water bodies has come down by 12.5%, and there is a significant drop in vegetation cover. The LST of the regions with the densely built-up area is high compared to the other types of land use. A mean rise of 4.8 °C in the LST has been noticed over the study area during this period. Few monitoring points representing rural areas within the proximity of the study region have been established, and the LST is monitored explicitly. As a result, it has been observed that the temperature in rural areas is relatively lower than the city region, which confirms the urban heat island effect. A micro-level study has been conducted by dividing the study area into four zones as per administrative boundaries. Statistical analysis using the zonal attributes affirms a positive correlation of 0.55 between LST and the built-up area. In contrast, a negative correlation of 0.52 between LST and vegetation cover is observed. The LULC results are validated using Google Earth Images captured at a finer resolution. Being selected as one of the cities under the smart city mission by the Urban Development Ministry of Govt. of India, it is expected that the land use pattern in Visakhapatnam will change drastically in the coming years. The findings of this study foster the relationship between LST and LULC, and the conclusions thus drawn would help planners for the sustainable development of Visakhapatnam.

     

Associations between plasma concentrations of PCB 28 and possible indoor exposure sources in Danish school children and mothers

BackgroundPolychlorinated biphenyls (PCBs) are ubiquitously present in the environment and are suspected of carcinogenic, neurotoxic and immunotoxic effects. Significantly higher plasma concentrations of the congener PCB 28 occur in children compared to adults. Exposure in schools may contribute to this difference.ObjectiveTo determine whether increased blood plasma concentrations of PCB 28 in Danish school children and mothers are associated with living in homes or attending schools constructed in the PCB period (1959–1977).MethodsPCB 28 was analyzed in plasma samples from 116 children aged 6–11 years and 143 mothers living in an urban and a rural area in Denmark and participating in the European pilot project DEMOCOPHES (Demonstration of a study to COordinate and Perform Human Biomonitoring on a European Scale). In Denmark, PCBs were used in construction in the period 1950–1977, and year of construction or renovation of the homes and schools was used as a proxy for indoor PCB exposure. Linear regression models were used to assess the association between potential PCB exposure from building materials and lipid adjusted concentrations of PCB 28 in plasma, with and without adjustment for potential confounders.ResultsAmong the 116 children and 143 mothers, we were able to specify home construction period in all but 4 children and 5 mothers leaving 111 children and 138 mothers for our analyses. The median lipid adjusted plasma PCB 28 concentration was 3 (range: 1–28) ng/g lipid in the children and 2 (range: 1–8) ng/g lipid in the mothers.Children living in homes built in the PCB period had significantly higher lipid adjusted plasma PCB 28 concentrations compared to children living in homes built before or after the PCB period. Following adjustment for covariates, PCB 28 concentrations in children were 40 (95% CI: 13; 68) percent higher than concentrations of children living in homes constructed at other times. Furthermore, children attending schools built or substantially refurbished in the PCB period also had significantly higher (46%, 95% CI: 22; 70) PCB 28 concentrations compared to children attending schools constructed before or after the PCB period, while their mothers had similar concentrations. Adjustment for the most prevalent congener, PCB 153, did not change this effect of home or school construction. When both home and school construction year were included in the models, the increase in lipid adjusted plasma PCB 28 for children living in or attending schools from the PCB period was no longer statistically significant. The individual effect of home and school construction periods could not be evaluated further with the available data.ConclusionOur results suggest that PCB exposure in the indoor environment in schools and homes constructed during the PCB period may contribute significantly to children's plasma PCB 28 concentration. Efforts to minimize PCB exposure in indoor environments should be considered.     

Radioactivity level and soil radon measurement of a volcanic area in Cameroon

The radioactivity level of soils in a volcanic area in Cameroon was determined and discussed. Thirty soils samples were collected from Buea and Limbé cities located in the south-western Cameroon. These two regions are known for theirs volcanic grounds due to the presence of Mount Cameroon Mountain. The activity concentrations of natural radionuclides as well as that of the fission product were evaluated by gamma-ray spectrometry using a hyper-purity germanium detector (HPGe). The ranges of concentrations in the surveyed soils were 11-17 Bq kg(-1), 22-36 Bq kg(-1) and 43-201 Bq kg(-1) for (226)Ra, (232)Th and (40)K, respectively. The radioisotope (137)Cs was also found but in a very small amount. The outdoor absorbed dose rate 1m above ground with the corresponding annual effective dose rate, assuming a 20% occupancy factor was estimated. The radium equivalent and the external hazard index were also evaluated and results are compared with available data from other studies and with the world average value [United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR), 1988. Sources, Effects and Risks of Ionizing Radiation. Report to the General Assembly on the Effects of Atomic Radiation. United Nations, New York; UNSCEAR, 2000. Sources and Effects of Ionizing Radiations. Report to the General Assembly with Scientific Annexes. United Nations, New York]. A solid state nuclear track detector (SSNTD), LR-115 was used for soil radon measurements at a depth of 50 cm. The ranges of soil radon concentrations were 6.7-10.8 kBq m(-3) and 5.5-8.7 kBq m(-3) in Buea and Limbé, respectively. A positive correlation was found between concentrations of radium measured with gamma-spectrometry and the soil radon concentrations measured with the nitrate cellulose detectors. The results of this study provide the radioactivity level in soil of a volcanic area, which has been found to be within the safety limits. The south-western Cameroon can be considered as having normal natural background radiation.     

基于遥感数据的PM2.5与城市化的时空关系研究——以成渝城市群为例

采用1998~2013年卫星遥感影像反演的PM2.5全球高精度产品数据集，结合GIS空间分析、地理加权回归（GWR）以及地理探测器等方法，系统地分析了成渝城市群城市化与PM2.5分布之间的关系。结果表明：（1）1998~2013年成渝城市群城市化速度较快，城市区域的PM2.5均值明显高于非城市区域，说明城市化对PM2.5具有一定的影响；（2）近16 a PM2.5重心与城市重心整体上都向东南方向移动，且两者每年在经度上的波动方向基本相反；（3）夜间灯光数据与PM2.5在空间分布上具有较好的一致性，且1998~2013年两者的GWR全局R2在0.86~0.95之间，相关性显著，研究区内城市化和人类活动对PM2.5的分布具有明显影响；（4）地理探测分析表明不同城市化因子对PM2.5影响差异显著，从2006到2013年城区人口密度和建成区绿化覆盖率逐渐成为成渝城市群PM2.5分布的主要影响因子。     

基于时空距离的江苏省景区系统聚集分形演化研究

运用聚集分形模型,将近10年分为4个研究时间点,从时空距离探讨江苏全省及其3大区域的高等级景区系统的聚集分形演化特征。结果显示：(1)各区域景区系统均呈聚集态,且苏北和苏中的聚集程度高于苏南与全省;(2)各区域景区系统都在向均匀模式演变;(3)各区域景区系统基于时间距离的空间结构比基于空间距离的结构,更接近于均匀模式;(4)苏北与苏中各区域内景区之间的交通网络水平低于苏南与全省;(5)各区域景区系统基于时间距离的演变,快于本区域基于空间距离的演变速度。研究结论可为江苏景区空间的合理布局提供一定的参考     

Effect of cigarette smoking on residential NO2 levels

Two studies evaluating the levels and sources of nitrogen dioxide in approximately 90 employee homes in the Richmond area with continuous sampling during the weeks of August 5, 1980, and February 9, 1981, were performed using samplers in the living room, bedroom, kitchen, and outdoors. Additional data were collected concerning appliance usage, heating/cooling plant, ventilation and cigarette smoking. Results were analyzed using BMDP routines. The largest contributor to NO₂ concentration was found to be gas-fired kitchen appliances. The mean kitchen level for homes with gas appliances during the winter study was 188 μg/m³. Excluding participants with gas kitchens, incremental influence due to cigarette smoking was detected. The 7-day, 3-room average level of NO₂ in the homes of nonsmokers and smokers without gas-fired appliances was 12 and 15 μg/m³, respectively, in the summer. The corresponding winter values were 19 and 22 μg/m³. Furthermore, the individual levels of NO₂ in the homes of smokers were generally below both the adjacent outdoor level and the National Ambient Air Quality Standard limit for annual exposure.