SEARCH

SEARCH BY CITATION

Keywords:

  • air pollution;
  • dust storm;
  • hospital admission;
  • respiratory diseases

ABSTRACT

  1. Top of page
  2. ABSTRACT
  3. INTRODUCTION
  4. METHODS
  5. RESULTS
  6. DISCUSSION
  7. ACKNOWLEDGEMENT
  8. REFERENCES

Background and objective:  The harmful effect of dust storm on lung health is controversial. This study aimed to assess any associations between dust storms and emergency hospital admissions due to respiratory disease in Hong Kong.

Methods:  Data on daily emergency admissions for respiratory diseases to major hospitals in Hong Kong, and indices of air pollutants and meteorological variables from January 1998 to December 2002 were obtained from several government departments. We identified five dust storm days during the study period. Independent t-tests were used to compare the mean daily number of admissions on dust storm and non-dust storm days. Case-crossover analysis using the Poisson regression was used to examine the effects of PM10 to emergency hospital admissions due to respiratory diseases.

Results:  Significant increases in emergency hospital admission due to COPD were found 2 days after dust storm episode. The relative risk of PM10 for lag 2 days was 1.05 (95% CI: 1.01–1.09) per 10 µg/m3.

Conclusions:  Dust storms have an adverse effect on emergency hospital admission for COPD in Hong Kong. This also suggests the adverse effect of coarse particles on lung health.


INTRODUCTION

  1. Top of page
  2. ABSTRACT
  3. INTRODUCTION
  4. METHODS
  5. RESULTS
  6. DISCUSSION
  7. ACKNOWLEDGEMENT
  8. REFERENCES

A dust storm is a meteorological phenomenon that arises when a gust front blows loose sand and dust off the surface of an arid or semiarid landscape. Soil particles are mass-transported by saltation and suspension, causing erosion from one place and deposition in another.1 The deserts of northern China are widely considered to be a major source of Asian dust,2 and dust storms originating from these regions have a far-reaching impact that has been reported not only within China3 but also in neighbouring countries such as Japan and Korea.4,5 Under certain weather conditions, wind-blown dust has travelled south towards Taiwan,6 and with a prevailing easterly wind, dust clouds can subsequently reach Hong Kong.7 Occasionally, dust storms may even travel across the Pacific Ocean to North America.8

Dust particles vary greatly in size. The largest are coarse particles, defined here as particulate matter ranging between 2.5 and 10 microns in aerodynamic diameter and commonly denoted by PM2.5–10. Fine particles (PM2.5) with aerodynamic diameter less than 2.5 µm are considered to be much more harmful. PM2.5 has frequently been the focus of air pollution and health studies.9,10 Smaller still are the ultrafine particles (PM0.1), with an aerodynamic diameter less than 0.1 µm. In a dust storm, the predominant fraction tends to consist of coarse particles,11 or the coarse fraction of PM10 (expressed as PM10–PM2.5). The adverse effects of coarse particles on morbidity and mortality have also been documented in several time series studies.12–14

Besides lowering visibility,15 dust storms can produce harmful effects on respiratory and cardiovascular health, as has been shown in several Asian studies.16–18 However, such an association has not been examined in Hong Kong, a subtropical metropolis in southern China. The aim of this study is to determine whether the risk of emergency hospital admissions due to respiratory diseases would be increased during and after dust storm episodes. We hypothesized that the mean number of hospital admissions for respiratory diseases would be higher during dust storms compared with that in the absence of dust storms.

METHODS

  1. Top of page
  2. ABSTRACT
  3. INTRODUCTION
  4. METHODS
  5. RESULTS
  6. DISCUSSION
  7. ACKNOWLEDGEMENT
  8. REFERENCES

Admissions data

Data on emergency hospital admissions for respiratory diseases recorded from January 1998 to December 2002 were obtained from the Hospital Authority, a Hong Kong public institution that provides more than 90% of all the hospital beds in the city. The daily number of emergency hospital admissions for all respiratory diseases (International Classification of Diseases (ICD)-9: 460–519), COPD (ICD-9: 490–492 and 494–496), and pneumonia and influenza (ICD-9: 480–487) were extracted for analysis.19

Pollution and meteorological data

Hourly concentrations of nitrogen dioxide (NO2), sulphur dioxide (SO2), ozone (O3), PM10 and PM2.5 recorded between January 1998 and December 2002 were obtained from the Environmental Protection Department (EPD). The EPD has 11 general air quality monitoring stations located in different districts throughout Hong Kong. All of the monitoring stations measured levels of the four ‘criteria air pollutants’: NO2, SO2, O3 and PM10. However, as PM2.5 was not classified as a ‘criteria air pollutant’, it was measured by only three stations.

SO2 was measured by ultraviolet florescence, NO2 by chemiluminescence and O3 by ultraviolet absorption. Both PM10 and PM2.5 were measured using the tapered element oscillating microbalance method. The 24-h mean concentrations of NO2, SO2, PM10 and PM2.5 were calculated. Because the formation of O3 is dependent on sunlight, a daytime 8-h mean concentration (taken from 09:00 to 17:00 h) was used for analysis. Daily averages of each pollutant were computed by averaging the mean concentrations from 10 of the 11 general air quality monitoring stations.* The mean daily temperatures and relative humidity for the same period were obtained from the Hong Kong Observatory.

Dust storm episodes

We defined a ‘dust storm episode’ as a period when the following four conditions were met:20,21

  • • 
    The Air Pollution Index exceeded 100 (indicating ‘very high’ pollution levels)
  • • 
    The ratio of PM2.5 to PM10 (by weight per unit volume) was less than 0.4
  • • 
    The wind profile was predominantly easterly§ and
  • • 
    The concentrations of dust storm tracer elements (e.g. aluminium) were at least three times higher during the dust storm episodes compared with the annual averages

According to the data from the EPD, three separate dust storm episodes—which affected Hong Kong for a total of 5 days—were identified between January 1998 and December 2002. These 5 days, which will be labelled as ‘index days’ or ‘dust storm days’ thereafter were 8 April 1999; 27 and 30 March 2000; and 6 and 10 March 2001.

Statistical analysis

Descriptive statistics were computed for daily numbers of hospital admissions, pollutant concentrations and meteorological variables by dust storm days and non-dust storm days within the 5-year study period. To eliminate the seasonal effect, descriptive statistics were also computed for only the non-dust storm days in March and April within the study period. An independent samples t-test was used to examine the difference between dust storm and non-dust storm days. Reliance on published and routine data precluded the need for institutional review board approval.

A case-crossover analysis was conducted to examine the effect of each episode on respiratory diseases. Because daily admissions are count data, a Poisson regression model was used and over-dispersion was accounted by quasi-likelihood method. Temperature, humidity, PM2.5, NO2, SO2 and O3 were included for adjustment. For each index dust storm day, four non-dust storm days were chosen as ‘controls’ for comparison. The four days selected were 7 days before and 7 days after the index day, and 14 days before and after the index day. Because the effects of a dust storm might be delayed for up to several days, besides examining the effect on emergency hospital admissions on the same day, effects up to 3 days later (lag 1, 2 and 3 days) were also examined. The relative risks of hospital admissions for respiratory diseases for changes in PM10 concentrations were computed. All the analyses were performed using R.22

RESULTS

  1. Top of page
  2. ABSTRACT
  3. INTRODUCTION
  4. METHODS
  5. RESULTS
  6. DISCUSSION
  7. ACKNOWLEDGEMENT
  8. REFERENCES

There were a total of 462 308 emergency hospital admissions due to respiratory diseases over the study period. Among them, 111 419 admissions (24.1%) were due to COPD and 74 513 admissions (16.1%) were due to pneumonia and influenza.

Table 1 shows the means and standard deviations of daily admissions, pollutant concentrations and meteorological variables by dust storm (index) and non-dust storm days (non-index). Compared with all non-dust storm days in the 5-year period, the mean concentrations of NO2, O3, PM10 and PM2.5 were all significantly higher on dust storm days, as were the number of hospital admissions for all respiratory diseases, COPD, and pneumonia and influenza. When the comparison was limited to non-dust storm days in March and April during the study period, the mean concentrations of NO2, O3, PM10 and PM2.5 were again significantly higher on dust storm days, as were the hospital admissions for all respiratory diseases and for COPD. By contrast, the humidity was significantly lower on dust storm days. For PM10, the mean concentration on index days (134.3 µg/m3) was more than 2.5 times greater than on non-dust storm days in March and April (53.2 µg/m3), and around 2.2 times greater when compared with the control days (60.0 µg/m3).

Table 1.  Mean (SD) number of daily hospital admissions, pollutant concentrations and metrological variables from January 1998 to December 2002, sorted by dust storm and non-dust storm days
 All respiratory diseasesCOPDPneumonia and influenzaTemperature (°C)Humidity (%)NO2 (µg/m3)O3 (8-hour) (µg/m3)PM10 (µg/m3)PM2.5 (µg/m3)SO2 (µg/m3)Coarse fraction (µg/m3)
  •  

    The coarse fraction was calculated by daily differences in the concentrations between PM10 and PM2.5.

Dust storm days (n = 5)328.280.255.421.271.879.662.5134.359.919.274.4
(27.7)(7.6)(10.0)(2.0)(5.4)(17.3)(21.8)(23.6)(17.0)(8.6)(16.6)
All non-dust storm days (n = 1822)253.061.040.823.778.057.737.049.935.217.214.9
(51.2)(14.5)(13.5)(4.9)(10.1)(19.9)(21.3)(24.6)(18.5)(11.0)(10.1)
P0.0010.0030.0160.2500.1720.0140.008<0.0010.0030.6830.001
Non-dust storm days in March and April (n = 301)285.467.750.622.082.160.235.153.235.316.818.2
(48.3)(13.0)(13.9)(3.1)(8.6)(16.0)(17.8)(25.9)(15.4)(10.5)(15.2)
P0.0500.0340.4440.6010.0080.0080.001<0.001<0.0010.601<0.001

Table 2 shows the adjusted relative risks (RR) of hospital admissions for all respiratory diseases and COPD associated with PM10 on dust storm days, in comparison with control days. The relative risks of emergency hospital admissions for COPD at lag 0, 1, 2 and 3 days were all greater than 1. The relative risk was 1.05 for 10 µg/m3 increase of PM10 at lag day 2 and was statistically significant (95% CI: 1.01–1.09). The relative risks of emergency hospital admissions for all respiratory diseases at lag 0, 1, 2 and 3 days were greater than 1 but were not significant. The relative risks for pneumonia and influenza were close to unity and not significant.

Table 2.  Adjusted relative risks (RR) of hospital admissions for a 10 µg/m3 increase in PM10
 Lag 0Lag 1Lag 2Lag 3
  • P < 0.05.

  •  Adjusted for PM2.5, NO2, SO2, O3 (8 h), temperature and humidity.

COPD
No. of hospital admissions on dust storm days80.2 (7.6)85.6 (12.3)85.4 (14.5)73.0 (19.1)
No. of hospital admissions on control days73.9 (15.7)73.9 (14.3)69.7 (11.8)71.5 (13.5)
Relative risk of hospital admissions1.06 (1.00, 1.12)1.02 (0.97, 1.07)1.05* (1.01, 1.09)1.00 (0.95, 1.06)
Pneumonia and influenza
No. of hospital admissions on dust storm days52.4 (9.4)58.2 (6.1)57.2 (55.8)55.8 (7.8)
No. of hospital admissions on control days55.0 (9.3)53.7 (6.1)58.5 (8.8)54.4 (7.8)
Relative risk of hospital admissions0.99 (0.93, 1.05)1.02 (0.99, 1.06)0.96 (0.92, 1.00)1.02 (0.99, 1.05)
All respiratory diseases
No. of hospital admissions on dust storm days328.2 (27.7)338.6 (32.4)328.0 (58.6)320.6 (56.8)
No. of hospital admissions on control days314.1 (45.4)307.8 (36.5)305.6 (33.2)313.2 (41.9)
Relative risk of hospital admissions1.03 (0.99, 1.08)1.02 (0.99, 1.06)1.02 (0.99, 1.06)1.01 (0.97, 1.05)

DISCUSSION

  1. Top of page
  2. ABSTRACT
  3. INTRODUCTION
  4. METHODS
  5. RESULTS
  6. DISCUSSION
  7. ACKNOWLEDGEMENT
  8. REFERENCES

Dust storms have been reported in ancient literature23,24 and have long been suspected of producing adverse effects on health.25 This study examined whether dust storms affected emergency hospital admissions due to respiratory diseases in Hong Kong. We have shown that the number of daily emergency hospital admissions due to COPD at 1 and 2 days after the index days were significantly higher than when compared with those on control days.

While fine particles (PM2.5) usually dominate the airborne particulates count on normal days, the predominant particulates during dust storms tend to be coarse particles.11 Dust storms thus provide good opportunities for us to examine the effect of coarse particles on lung health.

Most studies on air pollution and health focus on fine particulates of transport-related origin. Their small size implies deep penetration into the lung parenchyma. Furthermore, their complex chemical compositions, which may include a surface of toxic metals and polycyclic aromatic hydrocarbons, have been incriminated in the pathogenesis of several respiratory and cardiovascular diseases.26–28 Coarse particles, on the other hand, are mostly composed of crustal elements and considered to be less toxic. Nevertheless, they have been shown to trigger inflammatory processes, such as inducing cytokine release both in vitro and in animals.29–31 Becker et al. reported that coarse particles had larger effects than fine and ultrafine particles in inducing inflammatory mediators; they suggested that the effects were linked with the presence of microbial cell structures and endotoxins.32 Experiments on rats showed significant suppression of alveolar macrophage function and increased epithelial permeability after inhalation of coarse particles produced by re-suspending road dusts.33 The triggering of immunological response in the respiratory tract by high concentrations of coarse particles is a plausible mechanism that could explain the increase in hospital admissions for COPD patients during dust storms. A recent study in Korea has shown that Asian dust storm particles can induce toxicological effects on human skin through the activation of cellular detoxification system and production of various cytokines.34 Although many experimental studies had shown adverse effects of coarse particles on health, limited epidemiological studies are available in the literature.13,35

Studies on dust storms have focused on their adverse effects on health. Hefflin and colleagues reported a 4.5% increase in the number of emergency room visits 2 days after the PM10 levels exceeded 150 µg/m3.36 Recently, a significant association between Asian dust storms and hospital admissions due to pneumonia after one lag day was reported in Taipei,37 while the concentration of ambient influenza A virus was significantly higher during the dust storm days than during the background days in Kaohsiung City, Taiwan.38 Positive but insignificant associations between Asian dust storms and hospital admissions for COPD,18 asthma16 and cardiovascular diseases39 have been reported in Taiwan. However, time series in Hong Kong demonstrated significant and positive associations between PM10, and the risk of hospital admissions for COPD.40,41 Heavy dust events have recently been reported to be associated with an increased risk of asthmatic hospitalizations in children in Toyama, Japan.42

Our study provides further evidence of the adverse effects of dust storms or, more specifically, coarse particles on health. Having adjusted for other pollutants and confounding variables, there was a 5% increase in daily emergency hospital admissions per 10µg/m3 increase in PM10 due to COPD 2 days after a dust storm. The mean concentration of PM10 on dust storm days was 134.3 µg/m3—much higher than the mean concentration on non-dust storm days (53.2 µg/m3) in March and April. As coarse particles dominate PM10, this result can be interpreted as a 5% increase in daily COPD admissions per 10 µg/m3 increase in the concentration of coarse particles.

Meng and Zhang43 suggested that particulates from dust storms could cause oxidative damage in rat internal organs, although their study focused mainly on fine particulates. Schwartz et al.35 were dismissive of the role coarse particles may play in affecting human mortality—a conclusion partly supported by Brunekreef and Forsberg in their review,44 which reported that coarse particulates were not significantly associated with long- or short-term mortality in most urban areas, with only a few exceptions. However, the same review also mentioned that coarse particulate matter was associated with a strong short-term effect on respiratory health, including asthma and COPD, which can lead to increased hospital admissions. This conclusion is supported by our findings. Epidemiological studies by Ostro et al.45,46 have also found associations between PM10 and coarse particulates, and cardiovascular mortality.

Because the concentration of coarse particulates during a dust storm can reach levels several times higher than normal, the impact on community morbidity and the demand on hospital beds can be considerable. A better system for warning the public of impending dust storms is warranted. Specifically, those with chronic lung diseases should be advised to reduce outdoor exposure.

One advantage of studies on dust storms is that the high wind speed during such storms could diminish the concentration of other combustion-related pollutants, thus allowing us to differentiate more clearly the effect of the coast fraction of PM10 from that of traffic-generated PM2.5. We have also adjusted for the differences in the concentrations of PM2.5 between dust storm days and non-dust storm days. Hence, we can attribute the effect on hospital admissions for COPD to the coarse fraction of PM10 unambiguously. As for the other air pollutants, no positive significant effects were observed for hospital admissions due to ‘any respiratory diseases’, and ‘pneumonia and influenza’. Significant positive effects were observed on lag 3 days for COPD admissions with O3 (RR = 1.07; 95% CI: 1.02–1.12) and SO2 (RR = 1.15; 95% CI: 1.04–1.27). PM10 had no significant effect on lag 3 days.

One major limitation of our study is that dust storms episodes during the study period were rare; hence, statistical significance could not be reached even when all RRs were positive for any respiratory diseases and COPD. For comparison, we also conducted similar analyses on hospital admissions due to ‘any cardiovascular diseases’ (ICD: 390–459), ischaemic heart disease (ICD: 410–414), heart failure (ICD: 428) and cerebrovascular disease (ICD: 430–438). No significant differences were found in the number of hospital admissions with these diagnoses between dust storm days and non-dust storm days.

In conclusion, our study has demonstrated that dust storms affecting Hong Kong can cause a significant increase in local emergency hospital admissions due to COPD 2 days after the event. This has added new evidence to the adverse effects of coarse particles on pulmonary health. Timely health warning to those with chronic lung diseases to reduce outdoor activities during dust storm days may reduce their need for hospital admissions.

ACKNOWLEDGEMENT

  1. Top of page
  2. ABSTRACT
  3. INTRODUCTION
  4. METHODS
  5. RESULTS
  6. DISCUSSION
  7. ACKNOWLEDGEMENT
  8. REFERENCES

The authors want to thank the Environmental Protection Department, the Government of the HKSAR for providing the air pollution data and their advice on dust storm days.

REFERENCES

  1. Top of page
  2. ABSTRACT
  3. INTRODUCTION
  4. METHODS
  5. RESULTS
  6. DISCUSSION
  7. ACKNOWLEDGEMENT
  8. REFERENCES
  • 1
    Squires VR. Dust and sandstorms: an early warning of impending disaster. In: Yang Y, Squires V, Lu Q (eds) Global Alarm: Dust and Sandstorms from World's Drylands. United Nations, New York, 2001; 1573.
  • 2
    Zhang XY, Arimoto R, Zhu GH et al. Concentration, size-distribution and deposition of mineral aerosol over Chinese desert regions. Tellus 1998; B50: 31730.
  • 3
    Zhang J, Wu Y, Liu CL et al. Aerosol characters from the desert region of Northwest China and the Yellow Sea in spring and summer: observations at Minqin, Qingdao, and Qianliyan in 1995–1996. Atmos. Environ. 2001; 35: 500718.
  • 4
    Kanayama S, Yabuki S, Yanagisawa F et al. The chemical and strontium isotope composition of atmospheric aerosols over Japan: the contribution of long-range-transported Asian dust (Kosa). Atmos. Environ. 2002; 36: 515975.
  • 5
    In HJ, Park SU. A simulation of long-range transport of yellow sand observed in April 1998 in Korea. Atmos. Environ. 2002; 36: 417387.
  • 6
    Fang GC, Chang CN, Wu YS et al. Concentration of atmospheric particulates during a dust storm period in central Taiwan, Taichung. Sci. Total Environ. 2002; 287: 1415.
  • 7
    Fang M, Zheng M, Wang F et al. The long range transport of aerosols from Northern China to Hong Kong—a multi-technique study. Atmos. Environ. 1999; 33: 180317.
  • 8
    Husar RB, Tratt DM, Schichtel BA et al. Asian dust events of April 1998. J. Geophys. Res. 2001; 106: 1831730.
  • 9
    Sarnat JA, Schwartz J, Suh HH. Fine particulate air pollution and mortality in 20 US cities. N. Engl. J. Med. 2001; 344: 12534.
  • 10
    Pope CA III, Burnett RT, Thun MJ et al. Lung cancer, cardiopulmonary mortality, long term exposure to fine particulate air pollution. JAMA 2002; 287: 113241.
  • 11
    Yuan CS, Sau CC, Lee CG. Optical and chemical properties of atmospheric aerosols during continental dust storm periods at pencadores islands in Taiwan strait. Asian Dust/Visibility & Optical Properties, the 3rd Asian Aerosol Conference, Hong Kong University of Science and Technology, 2004.
  • 12
    Host S, Larrieu S, Pascal L et al. Short-term associations between fine and coarse particles and hospital admissions for cardio-respiratory diseases in six French cities. Occup. Environ. Med. 2008; 65: 54451.
  • 13
    Peng RD, Chang HH, Bell ML et al. Coarse particulate matter air pollution and hospital admissions for cardiovascular and respiratory diseases among Medicare patients. JAMA 2008; 299: 21729.
  • 14
    Malig BJ, Ostro BD. Coarse particles and mortality: evidence from a multi-city study in California. Occup. Environ. Med. 2009; 66: 8329.
  • 15
    Qiu YJ, Zou XY, Zhang GC. Research on impact of dust event frequency on atmosphere visibility variance: a case study of typical weather stations locating in the dust route to Beijing. Environ. Sci. 2006; 27: 104651.
  • 16
    Hong YC, Pan XC, Kim SY et al. Asian dust storm and pulmonary function of school children in Seoul. Sci. Total Environ. 2010; 408: 7549.
  • 17
    Yang CY, Cheng MH, Chen CC. Effects of Asian dust storm events on hospital admissions for congestive heart failure. J. Toxicol. Environ. Health A 2009; 72: 3248.
  • 18
    Chiu HF, Tiao MM, Ho SC et al. Effects of Asian dust storm events on hospital admissions for chronic obstructive pulmonary disease in Taipei, Taiwan. Inhal. Toxicol. 2008; 20: 77781.
  • 19
    World Heath Organisation. International Classification of Diseases, 1975 Revision. World Health Organisation, Geneva, 1977.
  • 20
    Lee YC, Hills PR. Cool season pollution episodes in Hong Kong. Atmos. Environ. 2003; 37: 292739.
  • 21
    Wai KM, Tanner PA. Case studies of Asian dust storm impacts on coastal site: implication of a good dust storm tracer. Water Air Soil Pollut. 2005; 168: 5970.
  • 22
    R Development Core Team. R: A Language and Environment for Statistical Computing. R Foundation for Statistical Computing, Vienna, 2008.
  • 23
    Liu T, Gu X, An Z et al. The dust fall in Beijing, China, on April 18. In: Péwé TL (ed.) Desert Dust: Origin, Characteristics, and Effect on Man. Geol Soc Am Special Paper 186 . Geological Society of America, Boulder, 1981; 14957.
  • 24
    Chun Y, Cho HK, Chung HS et al. Historical records of Asian dust events (Hwangsa) in Korea. Bull. Am. Meteorol. Soc. 2008; 89: 8237.
  • 25
    Williams PL, Sable DL, Mendez P et al. Symptomatic coccidioidomycosis following a severe natural dust storm. An outbreak at the Naval Air Station, Lemoore, Calif. Chest 1979; 76: 56670.
  • 26
    U.S. DHHS. Toxicological Profile for Polycyclic Aromatic Hydrocarbons. Agency for Toxic Substances and Disease Registry, Atlanta, GA, 1995.
  • 27
    Hertz-Picciotto I, Baker RJ, Yap PS et al. Early childhood lower respiratory illness and air pollution. Environ. Health Perspect. 2007; 115: 151018.
  • 28
    Brook RD, Franklin B, Cascio W et al. Air pollution and cardiovascular diseases: a statement for healthcare professionals from the expert panel on population and prevention science of the American Heart Association. Circulation 2004; 109: 265571.
  • 29
    Pozzi R, De Berardis B, Paoletti L et al. Inflammatory mediators induced by coarse (PM2.5–10) and fine (PM2.5) urban air particles in RAW 264.7 cells. Toxicology 2003; 183: 24354.
  • 30
    Happo MS, Salonen RO, Halinen AI et al. Dose and time dependency of inflammatory responses in the mouse lung to urban air coarse, fine, and ultrafine particles from six European cities. Inhal. Toxicol. 2007; 19: 22746.
  • 31
    Monn C, Becker S. Cytotoxicity and induction of proinflammatory cytokines from human monocytes exposed to fine (PM2.5) and coarse particles (PM10-2.5) in outdoor and indoor air. Toxicol. Appl. Pharmacol. 1999; 155: 24552.
  • 32
    Becker S, Soukup JM, Sioutas C et al. Response of human alveolar macrophages to ultrafine, fine, and coarse urban air pollution particles. Exp. Lung Res. 2003; 29: 2944.
  • 33
    Kleinman MT, Bhalla DK, Mautz WJ et al. Cellular and immunogenic injury with PM10 inhalation. Inhal. Toxicol. 1995; 7: 589602.
  • 34
    Choi H, Shin DW, Kim W et al. Asian dust storm particles induce a broad toxicological transcriptional program in human epidermal keratinocytes. Toxicol. Lett. 2011; 200: 929.
  • 35
    Schwartz J, Norris G, Larson T et al. Episodes of high coarse particle concentrations are not associated with increased mortality. Environ. Health Perspect. 1999; 107: 33941.
  • 36
    Hefflin BJ, Jecha L, Johnson CA et al. Surveillance for dust storms and respiratory diseases in Washington State, 1991. Arch. Environ. Health 1994; 49: 1704.
  • 37
    Cheng MF, Ho SC, Chiu HF et al. Consequence of exposure to Asian dust storm events on daily hospital admissions in Taipei, Taiwan. J. Toxicol. Environ. Health A 2008; 71: 129599.
  • 38
    Chen PS, Tsai FT, Lin CK et al. Ambient influenza and avian influenza virus during dust storm days and background days. Environ. Health Perspect. 2010; 118: 12116.
  • 39
    Chen YS, Yang CY. Effects of Asian dust storm events on daily hospital admissions for cardiovascular disease in Taipei, Taiwan. J. Toxicol. Environ. Health A 2005; 68: 145764.
  • 40
    Wong TW, Lau TS, Yu TS et al. Air pollution and hospital admissions for respiratory and cardiovascular diseases in Hong Kong. Occup. Environ. Med. 1999; 56: 67983.
  • 41
    Ko FWS, Tam W, Chan DPS et al. Temporal relationship between air pollutants and hospital admissions for chronic obstructive pulmonary disease in Hong Kong. Thorax 2007; 62: 77984.
  • 42
    Kanatani KT, Ito I, Al-Delaimy WK et al. Desert-dust exposure is associated with increased risk of asthma hospitalization in children. Am. J. Respir. Crit. Care Med. 2010; 182: 147581.
  • 43
    Meng Z, Zhang Q. Oxidative damage of dust storm fine particles instillation on lungs, hearts and livers of rats. Environ. Toxicol. Pharmacol. 2006; 22: 27782.
  • 44
    Brunekreef B, Forsberg B. Epidemiological evidence of effects of coarse airborne particles on health. Eur. Respir. J. 2005; 26: 30918.
  • 45
    Ostro BD, Hurley S, Lipsett MJ. Air pollution and daily mortality in the Coachella Valley, California: a study of PM10 dominated by coarse particles. Environ. Res. 1999; 81: 2318.
  • 46
    Ostro BD, Broadwin R, Lipsett MJ. Coarse and fine particles and daily mortality in the Coachella Valley, California: a follow-up study. J. Expo. Anal. Environ. Epidemiol. 2000; 10: 4129.
Footnotes
  • *

    Data from the air monitoring station in the remote island of Tap Mun, whose readings reflect background air pollutant levels, were excluded from the analysis.

  • When any one of the four ‘criteria air pollutants’ reaches its respective short-term Hong Kong Air Quality Objective (8-h mean concentration for O3 and 24-h mean for the other three pollutants), the ‘Air Pollution Index’ was arbitrarily defined as 100.

  • According to unpublished data from the Environmental Protection Department of Hong Kong, the ratio of PM2.5 to PM10 in Hong Kong during non-dust storm days is about 0.7.

  • §

    Southern China, including Hong Kong, is shielded from sandstorm blown directly from the north by tall mountain ranges in Central China. It is only affected when easterly wind brings the sandstorm from the sea.