Tag: Research

Breathe better, increase your productivity!

by Maria Restrepoin Featured

Productivity across all levels of employment matters and business leaders struggle to make sure it is optimized by investing in training, team building, office settings, freebies and many other proven strategies. However, 15 years of research has shown a close link between air quality and productivity that are the basis for green buildings and better indoor air management.

For many years we have known about the sick building syndrome (SBS), which are the common ailments that arise from time spent in a particular building and being exposed to poor ventilation or air filtration, outgasses from building materials, volatile organic compounds (VOC) and molds. Common ailments resulting from SBS are: headache, dizziness, nausea, eye, nose or throat irritation, dry cough, itchy skin, poor concentration, fatigue, voice hoarseness, allergies, cold, increased asthma and flu-like symptoms. And it all escalates to affect our congnitive capacity and productivity. So efforts to reduce both indoor and outdoor air pollution are actually investments in productivity, human capital and economic development.

The earliest known research on air quality and productivity dates back to 1999. Since then many studies on packers, call centers, farmers and even football players have confirmed that poor air quality has a negative effect on productivity, both indoors and outdoors.

In 2011, the National Bureau of Economic Research looked at farm workers output and ozone levels. They found that a decrease of 10ppb in Ozone concentrations increases worker productivity by 4.2%. Overall the research found that even at lower levels of Ozone than the standard, there were negative impacts on productivity and its strict regulation would yield benefits in health, productivity and possibly other areas. This was followed in 2014 by a research at Columbia, the University of South California and the University of California-San Diego where researchers looked into the effect of PM2.5 on pear-packers in California. It was found that just a 10 unit increase in PM2.5 decreased productivity by approximately 6% and that productivity is affected even below US standards. Moreover, Harvard University researchers recently assessed the effect of air quality in knowledge workers, those who are indoors mostly in front of a computer throughout their work day. They analysed Ctrip productivity in China against indoor air quality and found that workers are 5-6% more productive when air pollution is 0-50 AQI compared to 150-200 AQI. In a separate research by Harvard and Syracuse University, researchers looked into VOCs, CO2 and productivity. In addition to confirming the negative effect of air pollution on cognitive function, they specifically found that the greatest change (up to 15%) was observed in those cognitive functions involved in crisis response, information usage and strategy.

This body of research has shown how important it is to look into ways to improve indoor air quality. John Mandyck, chief sustainability officer for the NYSE listed United Technologies Corporation (UTC) said:

So what can we do with all those buildings that are old or just not green?

  • Control biological contaminants such as bacteria, viruses, fungi (including molds), dust mite and pollen. These may result from poor maintenance and housekeeping, water spills, inadequate humidity control.
  • Control chemical pollutants such as tobacco smoke, emissions from products, new furnishings, building materials or cleaning products.
  • Control particles. Particles are solid or liquid substances of dust or dirt from outdoors or other activities such as printing, painting or operating equipment.

Let’s:

  • Make sure ventilation is adequate and not obstructed.
  • Make sure the air is filtered to reduce particles.
  • Make sure to use safe cleaning products and best practices for machine operation.
Know your indoor air quality, control possible pollution sources, implement measures to improve air quality and make sure you are providing the best environment to nurture productivity!

Sources:

NIH – The Sick Building Syndrome

Harvard Business Review – Air Pollution is Making Office Workers Less Productive

INSIDER – The pollution outside your office window affects your work.

EPA – An Office Building Occupants Guide to Indoor Air Quality

The World – Want better thinking and productivity? Improve the air quality in your office.

We consume, ergo we pollute!

by Maria Restrepoin More news

So much is said about the appalling air pollution in China, how its citizens suffer and how only the rich can take adequate protective measures. But so little has been said about how we may all be linked to this pollution, even if we have never set foot in China.

Researchers from Tsinghua University, University of California and other institutions have recently published a paper with very interesting data on how we all bear the brunt of air pollution in China and how pollutants aided by global air currents reach neighboring countries  and affect the health even of those who leave in distant territories. This gives us an idea of the uncontrollable and controllable components of air pollution.

This research looked at PM2.5 (fine particulate matter) in 13 regions across 228 countries, and found that 12% of premature deaths (410,000) globally result from pollutants emitted in a different country, but which are often moved around by global wind conditions. While this result shows us how difficult it is to run away from air pollution that sees no real borders, it definitely makes us see the relevance of monitoring air quality regardless of how far we live from sources of pollution.

At the same time, this study explains how we all bear the brunt of air pollution in China and other countries of Asia. In fact, 90% of air pollution-related global mortality comes from power stations, airplanes, shipping and factories. All elements that constitute global trade. The ever-expanding nature of markets have made cheap products that flood western markets, the basis of a considerable amount of pollution in the East: China, India, Indonesia etc.

Cheap products are produced in Asian countries for a number of reasons – cheap labor and a lack of environmental regulations, which means that the process of production is highly contaminated and contributes to air pollution not to mention water or soil contamination. In addition, these products are produced far away from the place of their consumption so shipping and airplanes need to be heavily used to freight them to their end users.

Dr Qiang Zhang, one of the researchers, revealed that in 2007 consumption in the United States and Western Europe was tied to 110,000 premature deaths in China. In fact, the minute we buy cheap products, we are unconsciously increasing our share in air pollution.

“If the cost of imported products is lower because of less stringent air pollution controls in the regions where they are produced, then the consumer savings may come at the expense of lives lost elsewhere,”

This is why their main message is:

“We need to move our lifestyles away from cheap and wasteful,” Qiang Zhang

This research clearly shows the need to measure air quality and act to protect ourselves, regardless of how far we live from the source of pollution. And secondly, makes us understand how our consumption patterns can make a difference in the air quality suffered in other regions of the world.

Sources:
The Guardian – Thousands of pollution deaths worldwide linked to western consumers
HuffPost – Air Pollution Links People Thousands Of Miles Apart In Deadly Ways
The Economist – Airborne particles cause more than 3m early deaths a year
Nature – Transboundary health impacts of transported global air pollution and international trade

The Air We Breathe and Its Secret Path To The Brain

by Maria Restrepoin Featured

Previous research had shown a correlation between increased pollution and Alzheimer’s disease; between developing brains exposed to air pollution and mental health; and a link between air pollution and cognitive function in older men. Researchers are increasingly looking at these links and gathering evidence on yet another health effect of the polluted air we are exposed to.

The olfactory system is a direct route for small particles into the brain, especially those small enough to escape through the olfactory bulb. We have recently talked about the link between air pollution and strokes, now a new research from Lancaster University published by the Proceedings of the National Academy of Science has found evidence of toxic nano-particles, which come from air pollution, in human brains and has led to a rich discussion on the possible link between air pollution and Alzheimer’s disease.

In this most recent research, which examined brain tissue from 37 persons from Mexico and Manchester (UK), toxic nano-particles from air pollution -particularly magnetite, have been found in the human brain along with platinum, cobalt and nickel. According to the researchers, the shape and the type of metal indicates that it can only have come from air pollution. Accumulation of metals in the brain is characteristic in Alzheimer’s disease and especially magnetite, which has been previously associated with brain damage in patients with such ailment.

Many scientists have commented on the research results and although it is undisputed that the metal nano-particles in the brain do come from air pollution, many consider that this is not proof that there is a link between air pollution and Alzheimer disease.

Nonetheless, the study explains how the route of these nano-particles into the brain is through the olfactory system. Those particles that are small enough to pass through the olfactory bulb to the brain can lodge in the brain, cortex, hippotalamus and many others almost without barriers. Particles that lodge deep in your lungs can be very damaging because they create inflammation, infection, cancer or go directly to the bloodstream to cause trouble in other parts of the body. However, particles that enter through the olfactory system can be even more damaging because they have direct entrance to the brain where they can damage or kill neurons or even hamper the bains’ immune system.

In fact, both the Alzheimer’s and Parkinsons disease present a loss of the olfactory system capacities very early on. For this reason, many recent studies look at those particles that can be inhaled and have a direct pathway to our brains. One in every 14 persons above 65 suffer from Alzheimer’s diseases.

September is the World Alzheimer’s month, we cannot ascertain that air pollution is linked to Alzheimer, but we can raise awareness on the direct route for nano-particles into our brain.

Protect yourself and your family from air pollution!

Sources:

…And now breast cancer?

by Maria Restrepoin More news

There has been an intense debate over the possible link between breast cancer and air pollution. FIGO- the International Federation of Gynecology and Obstetrics highlighted the discovery of a link between air pollution and breast cancer following an article published in the Breast Cancer Journal on the results of research conducted by the University of Florida. This was reported by mainstream media as an alarming call to women living in areas with high air pollution.

Do not panic!

But there is no need to panic, it’s very important to be cautious with scientific results. In fact, many organizations like Cancer Research-UK, BreastCancer and others jumped to clarify that finding a link does not mean that air pollution causes breast cancer. Two things can be highly correlated without implying causation.

We know and we’ve talked about how pervasive air pollution is in our bodies, affecting our lungs, circulation, diabetes, skin and many more. The link between air pollution and lung cancer is very well researched, many research teams have worked on this subject for decades and have found how it happens and why. All the other links of air pollution to diseases are still in the very beginning of compiling research results and while it is one thing to link air pollution with skin problems, it is another step entirely to link it with a life-threatening disease like breast cancer.

Be cautious and understand the risks

We should not panic, but we should know the extent of current research on this matter. The latest research was conducted by the University of Florida, US, and looked at the link between breast density and air pollution. They found that women living in areas with high pollution had denser breast tissue. Women with dense breast tissue are up to six times more likely to develop some form of breast cancer.

In 2010, another study by the Research Institute of the MUHC, McGill University and Université de Montreal also showed a link. This study mapped air pollution against breast cancer patients and found that women living near areas with higher levels of pollution were twice as likely to develop breast cancer than the rest. However, Dr Goldberg, a researcher at The RI MUHC said:

“For example, we don’t know how much the women in the study were exposed to pollution while at home or at work, because that would depend on their daily patterns of activity, how much time they spend outdoors and so on”

In the case of this study, what is interesting is that the motivation to study the link between air pollution and breast cancer was to try to understand why cancer rates were going up in general / in these particular high pollution areas. The results showed that it could be air pollution but it may well be some other factor that the study could not control. In fact, the researchers called for more research on this subject and more research on the biological explanation behind this possible link.

Before more scientific evidence is gathered, we should make it a habit to know the quality of the air we breathe and take actions to improve the quality of the air we are exposed to, both indoors and outdoors!

Is Air Pollution Changing our Gut Microbiota?

by Maria Restrepoin Featured

It may seem a far cry, but scientists have been studying the effects of particulate matter (PM) in our intestines, gut microbiota (previously referred to as gut flora) and its relation to the sharp increase of Inflammatory Bowel Diseases (IBD). There is not an overwhelming amount of research, but certainly for more than a decade institutes in several countries have researched the possible link between exposure to air pollutants and various parts of our digestive system.

These studies show why being careful about what we eat and drink can take us a long way in protecting our gut microbiota from air pollution. In fact, hereditary genes may explain only a fraction of the IBD and scientists have in the past two decades seen that environmental factors are important contributors to these diseases.

But how does PM reach our bowel/intestines?

Well, researchers have observed that there are two primary ways: first the lungs clear part of air pollutants through a process called ‘mucocialiary clearance’ towards the intestines; and second we ingest it through our water and food.

And what is the effect of PM in our bowel?

Scientists in this field suggest that air pollutants cause systemic inflammation and change of the intestinal microbiota. Research has shown correlation between air pollution and IBD but scientists call for caution in the interpretation of these results due to methodological weaknesses and suggest more research should be done. However,

“If this connection is found to be true, this could have important implications for public health since intestinal diseases are relatively common and cause significant morbidity and mortality in addition to their economic impacts. Understanding how pollution contributes to intestinal disease will identify potential interventions or help advocate for patients by reducing exposures to dangerous materials.” say Leigh A. Beamish, Alvaro R. Osornio-Vargas and Eytan Wine in their 2011 publication in the Journal of Crohns and Colitis.

More recently (2015), scientists from Canada published an article on how microbiota can be modified by air pollution and last moth a group of researchers also published an article on PM and its effect on gut microbiota and the link to cholesterol. Overall, there is increasing knowledge of the importance of maintaining a healthy gut microbiota as a protection against diabetes, obesity, metabolic disorders and IBD. Scientists have shown that air pollution affects both the composition and the function of microbiota. They concluded:

“Together, our study in IL-10−/− mice, in conjunction with previous experimental and epidemiological observations, strongly suggests that ingested particulate matter could trigger and accelerate the development of gastrointestinal inflammatory diseases” Salim, Kaplan and Madsen from the University of Alberta and Calgary.

As individuals, let’s start now to protect ourselves. We can eat organic, we can have a specific vegetable and fruit cleansing routine, we can filter our water. Let’s start minimizing our ingested air pollution to take care of our gut microbiota!

Sources:

NIH – Air pollution effects on the gut microbiota: a link between exposure and inflammatory disease

Nature – Ambient Ultrafine Particle Ingestion Alters Gut Microbiota in Association with Increased Atherogenic Lipid Metabolites

When global problems affect your local air

by Maria Restrepoin More news

In our day-to-day life we have all noticed that the morning after heavy rain it’s usually a clear and fresh morning with low levels of airborne pollution. Wind conditions usually blow pollution out of the cities and those peaks of harmful air are mostly in days with no air flow or precipitation.  Empirically we have experienced the fact that weather patterns have an effect on dissipating air pollution or not.

This past week, researchers from the Atmospheric Sciences, Georgia Institute of Technology –Atlanta, published a paper in Science Advances on the effects of arctic meltdown on air pollution in China. The research clearly shows the challenges faced by China to address its air quality problems. Until now, most critics have focused on the need for China to control its emissions and to strike a healthier balance between development and environment degradation. Authorities in China have an increasing interest in controlling air quality, have implemented emission caps and most importantly are now the country with the largest production of clean energy. However, air quality is far from improved and pollution has not decreased as was hoped. The relevance of this research is that it affirms, following weather modelling analysis, that in the Eastern Plains of China, emissions’ control is important but is not enough to improve air quality. In fact, major global climate change problems are playing a significant role in promoting the accumulation of air pollution in this region.

“The ventilation is getting worse,” said study author Yuhang Wang, an atmospheric scientist at Georgia Institute of Technology in Atlanta to The Guardian “We think climate change, as it is driving rapid warming of the Arctic, is having a large effect on pollution in China.” “The very rapid change in polar warming is really having a large impact on China, emissions in China have been decreasing over the last four years, but the severe winter haze is not getting better. Mostly that’s because of a very rapid change in the high polar regions where sea ice is melting and snowfall is increasing,” he said. “This keeps cold air from getting into the eastern parts of China, where it would flush out air pollution.”

This is a scientific example of how weather conditions affect the build-up of air pollution in a certain place. This helps us further connect the dots between the bad air quality that harms our health and global problems such as green-house gas emissions, climate change and melting of the Arctic sea ice.Emissions of greenhouse gases from human activity cause between half to two-thirds of the fall in summer ice. Scientists predict that if the Arctic sea ice melting continues along with a correspondent increase in Eurasian snowfall, extremely poor ventilation conditions will occur and air quality control will prove increasingly challenging to implement unless greenhouse gas emissions are reduced not only in China but globally. The National Snow and Ice Data Center (NSIDC) reported in February 2017 that: “Antarctic sea ice is nearing its annual minimum extent and continues to track at record low levels for this time of year. On February 13, Antarctic sea ice extent dropped to 2.29 million square kilometers (884,000 square miles), setting a record lowest extent in the satellite era.”  

Air pollution affects us ALL and is one more environmental problem that is made worse by climate change!

Sources:
The Guardian – ‘Airpocalypse’ smog events in China linked to melting ice cap, research reveals
Science advances – Arctic sea ice, Eurasia snow, and extreme winter haze in China
Science – Why is China’s smog so bad? Researchers point far away to a melting Arctic

Humans causing up to two-thirds of Arctic summer sea ice loss, study confirms

 

Economic growth vs. Environmental policies?

by Maria Restrepoin More news

This week we have a thought provoking discussion: environmental policy vs. economic growth. This has been at the heart of decisions in the last year with regards to the Paris Agreement, for sure the excuse of many developing nations to delay adoption of environmental policies. In fact, we are constantly debating about the apparent conflict between economic development and environmental protection policies.

The last 50 years have seen rapid urbanization process in many countries, with cities offering more economic opportunities and rural areas being left for the environmentalists and hard labour. Cities grow, innovation happens and with that pollution levels rise, car convenience increases emissions, electricity needs increased emissions and consumerism increases emissions even further. In this picture, cities as centers for growth and innovation should be discouraged if we want to control air pollution.

Researchers at Carnegie Mellon  published a research on the link between economic development, urbanization and pollution.

Interestingly enough, the research found that urbanization is the result of a higher quality of life, and cities are more efficient at delivering services such as electricity. The study found that cities have more pollution but pollution per capita is lower in cities than out of them, and environmental policy does mitigate how emissions increase when the population of a city increases. The study in US counties showed that metropolitan GDP and personal income scaled with population size and this was regardless of environmental policies. So, environmental policies did not have a negative effect in economic development in cities, they in fact reduced drastically the environmental damage and pushed for cleaner production practices hence fueling green innovation.

Environmental protection can only make things better for all! Let’s take action and push innovation to cleaner ways of achieving economic growth!

Monitor air quality, Act to breathe cleaner, Enjoy the benefits!

Strokes and What We Breathe

by Maria Restrepoin More news

When we think about the health effects of air pollution, our immediate thought goes to our lungs. But the silent threat of poor air quality reaches many unexpected areas of our body. In the past two decades, research has shown that strokes, heart attacks and irregular heart rhythms can result from exposure to air pollution especially among people at risk. Currently, nearly 15 million people suffer a stroke worldwide, out of which 6 million die and 5 million are left with disabilities, possibly severe. The latest study suggests that approximately 29.2% of global strokes are linked to air pollution and the strongest link (33.7%) was seen in developing countries were solid fuels are burned indoors for energy. In developed countries, the link is much weaker at 10.2%.

“A striking finding of our study is the unexpectedly high proportion of stroke burden attributable to environmental air pollution, especially in developing countries. Air pollution is not just a problem in big cities, but is also a global problem. With the ceaseless air streams across oceans and continents, what happens in Beijing matters in Berlin. Air pollution is one aspect of the fossil fuel and global warming problem, which is itself partly a result of westernisation and urbanisation, especially in India and China.” Professor Vladimir Hachinski, University of Western Ontario, London, Canada and Dr Mahmoud Reza Azarpazhooh, Mashhad University of Medical Sciences, Mashhad, Iran.

Asia is responsible for two-thirds of the global stroke mortality. The local situation is characterised by two distinct yet opposite trends 1. mortality following a stroke has been declining in North Asia (Korea, Japan, Taiwan and urban China) perhaps due to improved stroke care, albeit the occurrence (incidence) of stroke is apparently not declining, thus leaving a greater number of people with long-term care needs, and 2. southern Asia (India, Pakistan, Bangladesh, Indonesia) where life expectancy is increasing but risk factors such as hypertension, diabetes, obesity, cigarette smoking are not yet adequately addressed. Given that cardio-vascular diseases are particularly affected by small particles found in haze, smoke and dust and the high link found between strokes and pollution, air pollution may be playing a major role in stroke statistics in Asia.

Effects of air pollution in cardiovascular diseases and strokes may be immediate or long-term. Immediate effects happen in older persons and sensitive persons with the build-up of fatty deposits in the arteries, where accumulation of small particles may worsen the situation.[7] Long-term exposure to poor air quality may, according to research, facilitate and worsen atherosclerosis (hardening and narrowing of the arteries) a disease commonly associated with high blood pressure and heart attacks / strokes.

In conclusion, if you are a person at risk of cardiovascular diseases or not “The central theme here is to be careful,” said Dr Luepker from the American Heart Association and “Avoid situations where you are exposed to a high level of air pollution.”

Sources:

Circulation – Air pollution, Climate and Heart Disease
Science Daily – For the first time, air pollution emerges as a leading risk factor for stroke worldwide
BMJ – Stroke in Asia: geographical variations and temporal trends
NIH – Stroke in Asia: a global disaster

Air Pollution and Diabetes

by Maria Restrepoin More news

The International Diabetes Federation says diabetes mellitus (common diabetes) affects around 400 million people across the world. Research in the past 10 years has shown that environmental irritants in the air and water play a role in these figures. A number of studies have now shown that air pollution has a synergy with other dominant factors and accelerates the propensity for type 2 diabetes, also known as adult-onset diabetes.

At The Duke University rats were exposed to air with highly polluted air (similar to Beijing readings) or filtered air for 19 days. The group of rats exposed to the Beijing air had 50% higher cholesterol level, 46% higher triglycerides and 97% higher total cholesterol.

What is happening in Asia?

Yes! Many studies have been conducted analysing this relation in humans. A study by the German Center for Diabetes Research (DZD) and the Helmholtz Zentrum München showed how air pollution at the place of residence increases the risk of developing pre-diabetic insulin resistance.

“Whether the disease becomes manifest and when this occurs is not only due to lifestyle or genetic factors, but also due to traffic-related air pollution,” said Professor Annette Peters, director of the Institute of Epidemiology II at Helmholtz Zentrum München and head of the research area of epidemiology of the DZD.

“The results revealed that people who already have an impaired glucose metabolism, so-called pre-diabetic individuals, are particularly vulnerable to the effects of air pollution,” said Dr. Kathrin Wolf, lead author of the study. “Thus, over the long term — especially for people with impaired glucose metabolism — air pollution is a risk factor for type 2 diabetes.”

Researchers from King Saudi University, Saudi Arabia, further acknowledged that traffic associated pollutants, NO2 (nitrogen dioxide), tobacco smoke and particulate matter have the strongest link with diabetes. And researchers from Naples University in Italy quantified the risk of future diabetes between 10 and 27% associated with exposure to just a 10 μg/m3 increase of PM2.5. In the most recent research, a US study looked at 1000 Mexican-Americans and found that PM2.5 exposure was significantly associated with diabetes risk factors, with an effect equivalent to that of obesity, the authors noted.

What is happening in Asia?

Asia is affected by the double burden of high levels of air pollution and a high percentage of the population with diabetes. In fact, Asian countries have 60% of the world’s diabetic population. China alone is leading this statistic with 10% of its population (98 million) affected by diabetes. This is the result of a combination of factors: socio-economic growth and industrialization; urbanization spreading widely and notable lifestyle changes. Moreover, Asians have genetically a higher predisposition for diabetes, they develop diabetes earlier and with lower body mass index and waist circumference when compared with the Western population. Prof Juliana Chan of the Chinese University of Hong Kong says there is a complex interplay between genetic, lifestyle and environmental factors, which have been compounded by China’s rapid modernisation. Worryingly, if we combine the higher predisposition to diabetes, the nearly 50% smoking rate among adult men, the change of diet due to globalization and the very high air pollution levels, we can understand the extent of the risk in Asia.

What can we do about it?

Reduce the effect of air pollutants on your diabetes risk:

  • Avoid smoking or passive smoking;
  • Know your indoor air quality and control it;
  • Protect yourself when exposed to outdoor air, especially when its highly polluted;
  • Adopt a healthy diet; and
  • Increase your level of physical activity.

Sources:

Diabetes Journal – Air Pollution and Type 2 Diabetes

Science Daily – Air pollution, a risk factor for diabetes

NIH -Effect of environmental air pollution on type 2 diabetes mellitus

NIH – Particulate matter pollutants and risk of type 2 diabetes: a time for concern?

REUTERS – Air pollution not just bad for your lungs

TIME – Study: Air Pollution Heightens Risk of Obesity and Diabetes

Are you pregnant? We’ve got you covered! Tips to protect your bump from Air Pollution

by Maria Restrepoin More news

Air pollution is ubiquitous and our desire to have offspring is natural….well at least for some of us! Today we want to bring to you a few facts on what is known about exposure to air pollution during pregnancy for you and your bump.  Here are some useful and easy to follow safety tips.

Let’s start with the facts:

Research has shown that prenatal exposure to pollutants can increase the risk of low birth weight and preterm delivery, which contributes to infant mortality and developmental disabilities. We are usually concerned about outdoor air pollution: ozone, particulate matter etc but other pollutants of concern that we should always keep in mind are those mostly present indoors, such as household cleaners, fumes from paint and carbon monoxide in addition to particulate matter that is present indoors.

Some research has shown that particulate matter affects the fetal development because it alters the intrauterine environment. This ‘early-life’ stress is a contributor to conditions that will increase the risk of cardiovascular disease, cognitive function, diabetes, obesity and problems in the nervous system later in life.

“Healthy pregnancies in women result in healthy children. Healthy children make healthy adults, societies and nations.” Dr Sherin Devaskar, Mattel Executive Endowed Chair of the department of pediatrics at Mattel Children’s Hospital UCLA

Source:

Breathe Life 2030 – Air Pollution and Pregnancy (pdf)