Air pollution is strongly associated with morbidity and mortality cases across the word, and accurate assessment of its spatial and temporal variation is important for epidemiological studies to estimate the health effects . Air pollution is a major problem faced by the modern civilization having harmful toxicological bearings on the environment and human health . Airborne suspended particulate matter is a serious worldwide concern as it is linked with adverse human health conditions. There have been several epidemiological studies which revealed the association of airborne particulate matter with the incidence of acute and chronic respiratory diseases . Studies related to the exposure of airborne particulate matter have been documented in epidemiological studies related to human health impacts such as cardiovascular and respiratory diseases over last three decades and are broadly distinguished into acute or chronic on the temporal framework [4, 5]. Ambient air pollution contributes about 8% to the Global Burden of Diseases (GBD) and is increasing continuously with time due to increase in fine particulate matter (particulate matter having aerodynamic diameter less than or equal to 2.5 µm i.e., PM2.5) . Air pollutant such as nitrogen dioxide (NO2) is traffic generated air pollutant and harmful to human health . There is a paucity in research related to the health effects of NO2 exposures in smaller urban areas and there is reason to believe that effect of NO2 vary from urban to non-urban areas . Respiratory diseases are commonly encountered in medicine and pose a very high burden on healthcare infrastructure . Chronic obstructive pulmonary disease (COPD) is a one of the major causes of morbidity and mortality worldwide . The existing physical and socio-economic environment has a significant impact on the respiratory illness . According to the reports of GBD, there are almost 2 million premature deaths in India due to ambient air quality and household air pollution. 13 out of 20 cities (across the world) having highest annual level of PM2.5 are in India, which lead to 21% increase in mortality due to PM2.5 . Besides the variation in the air composition, the meteorological factors also play a very significant role in spreading of contagious air-borne diseases and air pollutants. Temperature, humidity, atmospheric pressure and wind speed are some of the important meteorological variables that determine the transport, dispersion, stability and growth of air pollutant and air borne pathogen in the ambient atmosphere [12, 13]. Low temperature and atmospheric stability provides ideal condition for growth of various airborne pathogens and accumulation of various air pollutants. Viruses such as human Metapneumovirus (hMPV) and respiratory syncytial virus (RSV) have been found to cause epidemics in winter season in cold and temperate regions . Mortality is considerably higher during the cold winter months (December–March) as compared to other seasons in northern hemisphere. In the United Kingdom, around 25,000 deaths occur annually during winter months . Cold winter months are not only associated with an increased number of deaths but also they have a substantial impact on morbidity . There is a constant increase in hospitalization and mortality during winter months, the bulk of which is related to cardiovascular and respiratory diseases . Exposure to severe cold environment has witnessed an increased rate of incidence of respiratory infections . The effects of climatic change, air pollution and its impact on human health and environment are often getting discussed during last two decades .
The Himalayan region stretches over 2400 kilometers from west- northwest (Nanga Parbit 8125 meters) to east (Namche Barwa 7755 meters) and is considered to be the roof of the world . Due to human population burst in the last few decades both the Himalayan ecosystem and human society is facing odd environmental changes . Climate change, pollution and continuous land use transformation in the Himalayan region have impacts on human health, where ecological changes and economic inequalities further influence the spread of various kinds of diseases . Unique geographical personality (physical, socio-economic and cultural environment) of the Himalayan region are linked to different morbidity pattern associated with several respiratory tract infections . These geographical aspects of human health could be due to high variability in climatic conditions and atmospheric stability within Himalayan region . Air quality deteriorates significantly during winter months in the Valley region of Kashmir (Himalayas) with highest PM2.5 concentrations (~ 350 µg/m³), which is about six times of the Indian permissible limit . Emissions in the valley region of Kashmir are highest during winter months due to low temperature and dry conditions along with elevated rise of biofuel emissions (burning of leaves and twigs). These biofuels are mostly byproduct of agriculture and horticulture residuals and are found to be the potent causes of rise in pollution level. Back trajectories show the role westerly winds in the contribution of high PM2.5 levels in the Kashmir Himalayas originated mainly from Afghanistan and other surrounding areas . Studies conducted at the Kullu-Manali region of lower Himalaya have shown that the vehicular pollution is producing ultrafine particles which are getting readily absorbed by lungs and causing serious respiratory and neurological disorders . The mechanisms underlying the seasonal variations are not completely elucidated, but can be surely attributed to the changes in the outside and inside air temperature, wind chill factors, exposure to sunlight, air pollution, pattern or food intake and psychological conditions . The relationship between air changes per hour and infection transmission in a closed environment is enigmatic and have a direct impact on incidences of infectious diseases . A study conducted in seven cities situated in the crop burning area of north India has shown the dependence of various pollutants concentration on the meteorology . The concentration of pollutants such as carbon monoxide and volatile organic compounds have been found to be directly linked to atmospheric conditions, causing major respiratory damages to the population . Damage to respiratory and cardiac health due to criteria air pollutants have been found in the Delhi and also revealed the possible health damage to other places due to transport of these pollutants to other regions .
Himalayan region is a very cold and temperate region which gets even colder in winter season with humid and stable atmospheric conditions . With the transport and buildup of harmful air pollutants, such stable atmospheric conditions contribute to damaging of respiratory system making it more susceptible and less defensive against further infections such as acute respiratory infections (ARIs) . ARIs include serious respiratory health problems faced mainly by children and elderly population and are caused mostly by viruses .
In most of the studies done worldwide ARIs are found to be linked with the meteorological factors such as temperature, humidity and wind speed [30, 31]. In India, there has been wide research gaps correlating the incident of respiratory diseases with the environmental factors and we haven’t found any study relating respiratory diseases with the meteorological variables and air pollution in Himalayan region. Therefore, with very rapidly changing climatic conditions and transport of pollutants in Himalayan region, the effect of air pollution and meteorological conditions needed to be studied with respect to respiratory health.