A Fresh Air Look at Ventilation

Environmental factors contribute to the spread of microorganisms causing diseases. Sunlight can kill viruses in minutes, while increased air pollution could be one of the risk factors of more severe outcomes. Humidity is also thought to be important. A team of scientists from Northeast US analyzed COVID-19 cases from 2669 counties and found that cold and dry weather and low levels of ultraviolet radiation are moderately associated with increased SARS-CoV-2 transmissibility, with humidity playing the largest role. 17.5% of the virus’ reproductive number was attributable to meteorological factors, with temperature accounted for 3.73%, humidity accounted for 9.35%, and UV radiation for 4.44%. This is in line with earlier findings about SARS-CoV-2 being less stable at higher humidity and warmer temperatures in human nasal mucus and sputum. Like in previous environmental studies, however, these fractions were not the same everywhere and were higher in northern counties. 

20 years ago, American scientists Wells and Riley developed a model of the airborne transmission of infectious diseases such as tuberculosis and measles. A novel modified version of this model was used to estimate the impact of relative humidity on the removal of respiratory droplets containing infectious virus particles. The results showed that this impact depended on the ventilation rate and the size range of virus-laden droplets.  It was concluded that increasing the ventilation rate is more beneficial, while installing and running humidifiers may not be an efficient solution to reduce the risk of COVID-19 disease in indoor spaces. 

A popular metric for airflow is Air Changes per Hour (ACH, also called Air Change Rate).  It tells how many times the air within a space can be replaced with fresh air each hour. Increasing the ventilation rate from 0.5 ACH to 6 ACH was predicted to decrease the infection risk by half. Studies of US houses and apartments found typical ACH values between 0.5 and 2.0 (with open windows). 4.0 ACH is the minimum air exchange rate acceptable for commercial buildings, but 1.5 ACH is the reality for most schools. Opening a car window raises ACH to 6.  Natural ventilation combined with novel technologies could help to increase fresh air intake with minimal energy cost.

Virus clouds can, indeed, be dispersed with some fresh, clean air. But fresh air isn’t going to stop the spread of microorganisms in high-density crowds. Effective ventilation is only one of basic infection control strategies along with hand/environmental hygiene, social distancing, case surveillance and other evidence-based measures. 

REFERENCES

Aganovic A, Bi Y, Cao G, Drangsholt F, Kurnitski J, Wargocki P. Estimating the impact of indoor relative humidity on SARS-CoV-2 airborne transmission risk using a new modification of the Wells-Riley model. Building and environment. 2021 Aug 23:108278.

Ma Y, Pei S, Shaman J, Dubrow R, Chen K. Role of meteorological factors in the transmission of SARS-CoV-2 in the United States. Nature Communications. 2021 Jun 14;12(1):1-9.

Cities of the Future

Picture your dream home. Chances are you did not think much about cutting edge technology, but more about luscious green grass, backyard oasis, fresh clean air, soothing pool of water or watching the sunset in your rocking chair.

Scientific studies and crowdsourcing projects  showed that the amount of greenery is usually associated with beauty, quietness, or happiness, while broad streets, fortress-like buildings, and council houses are associated with ugly, noisy, and unhappy environments.

But, as most people now live in cities and urban dwellers are likely to reach 70% of the world population by 2050, will it be actually possible to build happy cities where we can relax and rejuvenate?

Perhaps we could start from a cleaner air by spraying water from sprinklers? According to Shaocai Yu, this is a technologically feasible and cost efficient option reducing the particle load in a very short time. And it is already utilized in  Lanzhou, the largest city of China's Gansu province. Two giant water cannons will squirt water 2,000 feet into the air and bring the pollutants down to earth. It won't stop pollution elsewhere, though, will need to be done daily, and in addition to other measures.

How to design a mentally rejuvenating city? Research shows, that even in a dense urban area at the bottom of a concrete canyon, we could feel a little better if there is more architectural variety. Yet, isn't it better if the city keeps in touch with nature?

25 Verde, a five-story apartment complex in Turin, Italy designed by Luciano Pia, features 150 potted trees that absorb almost 200,000 liters of carbon dioxide an hour, offering extra shade during the summer months. And every plant and tree offer the needed variety of color, foliage, and blooms!


Meanwhile the Netherlands is experimenting with floating houses. Singapore, too, is thinking about syncing design with the environment. And, if you have a million to spare, you can buy a house in Dubai with underwater views and outdoor climate-controlled streets.

Most of the world's population growth will happen in low and middle income cities with unhealthy housing. The challenge is in finding affordable ways to improve the aesthetics and health of neighborhoods. And it might be easier than you think!

REFERENCES

Daniele Quercia, Neil Keith O'Hare, & Henriette Cramer (2014). Aesthetic capital: what makes London look beautiful, quiet, and happy? Proceedings of the 17th ACM conference on Computer supported cooperative work & social computing, 945-955 DOI: 10.1145/2531602.2531613

Lindal, P., & Hartig, T. (2013). Architectural variation, building height, and the restorative quality of urban residential streetscapes Journal of Environmental Psychology, 33, 26-36 DOI: 10.1016/j.jenvp.2012.09.003

Shaocai Yu (2014). Water spray geoengineering to clean air pollution for mitigating haze in China’s cities Environmental Chemistry Letters : 10.1007/s10311-013-0444-0

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Kardan, O. et al. (2015) Neighborhood greenspace and health in a large urban center. Sci. Rep. 5, 11610; doi: 10.1038/srep11610. PMID: 26158911

Asthma in September

Asthma sufferers know that when it rains it spores - as fungi and mold get moving through the air. But many don't realize that the most dangerous month for children's asthma symptoms is dry September.

A study of hospital data in New York City found the spike in admissions in two to three weeks after the return to school. Additional New York studies indicated that cold and dry weather in autumn mostly increased admissions in the school-aged population (<18), while hot and dry weather in the summer caused spikes in asthma admissions across all ages. Doctor visits increase every September in many Northern Hemisphere countries. It happens in the United States, the United Kingdom, Mexico, Israel, Finland, Trinidad, and Canada, where 20% to 25% of all childhood asthma exacerbations requiring hospitalization have occurred in September.

Asthma hospitalizations in children 2-15 years in Canada

As students return to school, they are exposed to an increased number of indoor allergens, irritants and health risks. The "flu season" is approaching, weed pollen is not over yet, and indoor air is filled with pests, mold,
dust mites, animal dander, chalk
dust, cleaning agents, scented and unscented
personal care products and fumes.

So what can you do to manage asthma at school? Home environment is easier to control, but if you know your triggers, you can develop a plan - like asking teachers that pet animals with fur and feathers are not kept inside classrooms, dry-erase boards or " dustless" chalk are used instead of regular chalk and making sure that kids with asthma have reliable friends that can support them. 

REFERENCES

Sears MR, & Johnston NW (2007). Understanding the September asthma epidemic. The Journal of allergy and clinical immunology, 120 (3), 526-9 PMID: 17658590

Lin S, Jones R, Liu X, & Hwang SA (2011). Impact of the return to school on childhood asthma burden in New York State. International journal of occupational and environmental health, 17 (1), 9-16 PMID: 21344814

Lee CC, Sheridan SC, & Lin S (2012). Relating weather types to asthma-related hospital admissions in New York State. EcoHealth, 9 (4), 427-39 PMID: 23224756

Choi IS, Lee SS, Myeong E, Lee JW, Kim WJ, Jin J. (2013) Seasonal variation in skin sensitivity to aeroallergens. Allergy Asthma Immunol Res. 2013 Sep;5(5):301-8. doi: 10.4168/aair.2013.5.5.301.

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Rosas I, McCartney HA, Payne RW, Calderon C, Lacey J, Chapela R, et al. Analysis of the relationships between environmental factors (aeroallergens, air pollution, and weather) and asthma emergency admis­sions to a hospital in Mexico City. Allergy 1998;53:394-401.

Garty BZ, Kosman E, Ganor E, Berger V, Garty L, Wietzen T, et al. Emergency room visits of asthmatic children, relation to air pollution, weather, and airborne allergens. Ann Allergy Asthma Immunol 1998; 81:563-70.

Harju T, Keistinen T, Tuuoponen T, Kivela S-L. Seasonal variation in childhood asthma hospitalizations in Finland, 1972-1992. Eur J Pediatr. 1997;156:436-9.

Monteil MA, Juman S, Hassanally R, Williams KP, Pierre L, Rahaman M, et al. Descriptive epidemiology of asthma in Trinidad, West Indies. J Asthma 2000;37:677-84.