The precise measurement of Earth’s gravitational field is very important. By timing the period of a simple pendulum it might be possible to get a measurement for the field with accuracies to three significant figures but not much more than that. A key part of geophysics is to use variations in gravitational field strength at different points around the surface of the Earth to estimate subterranean densities. These variations can be found to such resolution that they can be used to study tectonic plates, volcanoes and even the decrease in mass of melting glaciers.
Last week I produced this post which begins with a quick sum up of a few times I’ve talked about air pollution in China. Now today we’re actually talking about air pollution not in China but in the second most populous country in the world: India. The air pollution in India is considered pretty bad and is likely a main contributor to health defects in the country. In the Indo-Gangetic Plain, the span of the county bordering Bangladesh and China, you will find PM2.5 concentrations, of up to 150 μg m−3 (remember that the World Health Organisation recommends a limit of 10 μg m−3) due to this strip containing Delhi, Dhaka, Kolkata and about 50% of the country’s population.
Coastal upwelling systems are one of the most important ecosystems in the world. A process called Ekman dynamics (which the more mathematically inclined can read about here, you may need to reload it a few times before the link works) acts to sweep water away from the coast and out into the open ocean. This action leads to the upwelling effect where cool water from the deep ocean is pulled up to the surface. These waters have been deep in the ocean where photosynthesis has been impossible leading these waters to contain more nutrients than those at the surface and as a result phytoplankton thrive in coastal upwelling systems. It is estimated that these habitats cover 2% of the world’s oceans but contribute about 7% of the world’s biomass production through photosynthesis.
In the past the conversation of China and air pollution has risen multiple times in this blog: here, here and here being three examples. Once again it is time to return to talk about the Chinese environment. The North China Plain is one of the most polluted regions of the country (and as a result, the world) due to a dense population and urbanisation that doesn’t seem to be showing signs of slowing in the near future. Beijing, naturally the largest city in the North China Plain, has been hit by severe hazing events repeatedly with the worse coming in January of 2013 where the concentrations of PM2.5, particulate matter of diameter less than 2.5 micrometers, was 500 μg m−3. Let’s be clear, the World Health Organisation has a recommended limit 10 μg m−3, many urban centres overshoot this but not 50 times overshoot it.
A chain is only as strong as it’s weakest link. An interestingly true phrase, amorphous materials like concrete or glass break along microcracks which are an inevitable part of their production. The finest evidence of this is that extensive stress will always break a sample of concrete before compressive stress does. Pulling the concrete separates and extends the cracks until failure occurs while compressing closes the cracks and prevents their growth. Today we won’t be talking about concrete or glass but rocks. The same concept applies however, small fractures running through the rock grow large until the rock fails withstand a force.
In a mixture of gasses the partial pressure of a particular gas is the amount of pressure that gas contributes to the whole. From the ideal gas law:
we see that since the volume and temperature of a mixture of gasses is same any of the gasses then really the partial pressure is really just determined by the ratios of the numbers of particles from each gas in the mixture. For instance the partial pressure of carbon dioxide (CO2) in the atmosphere grows by about 1.8 parts per million by volume (look at the equation to understand those units) every year. Although there is quite a lot of variation in the locations where CO2 is given off the ocean has, by in large, maintained a steady equilibrium in CO2 trade especially far from land in the open ocean. Considering that it takes approximately 10 months for an equilibrium to be reached between air and sea and that the water residence times on the open ocean is about 12 months it is no surprise that the partial pressures of CO2 on the surface of the oceans matches the partial pressure above them.
I have always found it quite amazing that the ancient civilisations all the way back to the Egyptians, Greeks, inhabitants of the Indus Valley and even people who came before them have always looked up at the same sky. Most people think of the stars and how they have remained so constant, but instead I think of the clouds. Art going back through the millennia have always depicted clouds as the same and there is no reason to think they would have changed much in this time. That has always been the thing that has struck me when I look up at the sky. But on to the actual physics. Clouds have always been important mediators of the Earth’s temperature with their ability to let through shortwave radiation from the sun and then trap the longwave radiation the Earth reemits. Continue reading Ion Condensation Increases Cloud Condensing Nuclei Clustering