With all windows shut, the air in my home turns over about once per ten hours

Over part of Christmas I was away for a few days. As you can see from the plot, this was long enough for the CO2 concentration inside my flat to relax to the atmospheric value (or close to that) of a bit over 400 ppm. The plot has time as the x-axis, starting at midnight of the day I left. I left at about midday of the first day and the CO2 concentration then relaxed back to about 450 ppm, and stayed there. The relaxation is well fit by an exponential function with a time constant of close to ten hours. The fit is the dashed cyan curve.

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Keeping the air you breathe at home reasonably fresh in winter

On Wednesday 14th December 2022 it was around freezing (0C) all day, and night. I worked at home in the morning to around midday, then was in work from midday-ish to five-ish. The plot shows the CO2 levels in my home for the 24 hours of that day, midnight to midnight. When I was home I kept small windows in my bedroom and kitchen open a few centimetres to keep some air turning over. As you can see from the plot, when I was at home the CO2 level was mostly between 800 and 1000 ppm (parts per million).

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AI-powered chatbot that can be scarily good, can be just as bad as the World Health Organisation

A new chatbot called chatGPT* is making waves. Some of its answers are scarily good. For example:

Question: What is a phase transition?

ChatGPT: A phase transition is a change in the physical state of a substance, such as a change from a solid to a liquid or a gas, or vice versa. Phase transitions are driven by changes in temperature, pressure, or other physical factors, and they can occur in both pure substances and mixtures. For example, water undergoes a phase transition from a liquid to a solid (ice) when it is cooled below 0 degrees Celsius, and it undergoes a phase transition from a solid to a gas (water vapor) when it is heated to its boiling point. The study of phase transitions is important in many fields, including chemistry, materials science, and meteorology.

ChatGPT (4th December 2022)

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A morning in the life of my personal ventilation status

Yesterday I went to the University of Bristol to give a seminar, on some of the physics of COVID-19 transmission. It was great to see the people there and chat, and I took along a CO2 monitor so my seminar could include some real-time data on how well ventilated the seminar room was. It turns out that the ventilation was not that great, but I then opened a window in the room and it got better. I am sure many more intelligent and better delivered seminars have been given at the University of Bristol Physics Department. But they can’t be many seminars during which the seminar a potential health hazard was identified by the speaker, who then partially addressed it during the same seminar.

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Evidence-based social distancing guidelines

Early on in the pandemic, social distancing measures were introduced, with various distances. The UK went for 2 m, the USA for 1.8 m (6 feet), Hong Kong 1 m, etc. None of these were based on much evidence, but we now know a lot more. COVID-19 is an airborne disease. Although more data is badly needed, it seems likely that somewhere between most, and almost all, infections are caused by breathing in virus, that an infected person breathed out seconds or minutes earlier. The virus is carried by tiny droplets suspended in the air. And most transmission is indoors.

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A day in the life of my CO2 exposure

Over the summer I am continuing to play around with my new toy: a CO2 meter. This measures the carbon dioxide aka CO2 in the air. A plot of the CO2 concentration over one complete day (Thursday 11th August 2022) is shown above. This is in my bedroom. The units are ppm = parts per million, so 400 ppm means that out of every million molecules in the air, 400 are CO2.

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Research into surfaces licked by someone infected with COVID-19

It looks likely that most, or perhaps almost all, COVID-19 transmission is directly airborne. An infected person breathes out the virus in tiny aerosol droplets, which someone else later breaths in. But people also worry about becoming infected from touching surfaces contaminated with virus. This has led to work looking at how long virus can survive on surfaces.

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The NHS has commissioned a review of aerosol generating medical procedures, I’d give it 60%: shows hard work, but let down by poor writing and selection, and unclear conclusion

I have been reading both students’ final-year-project reports and a report commissioned by the NHS. I don’t know whether to be happy or sad that some of our students can write better reports than an august panel that includes a number of members of Royal Colleges. On the one hand it is great to see our students doing so well, but on the other hand at any one time the NHS is treating millions of patients, and you would hope that infection control in NHS hospitals would have rather more competent oversight.

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