Milwaukee’s urban agriculture organizations have worked to secure longer leases for community gardens, but they have not succeeded in purchasing and preserving many of the sites, so most of the city’s gardens remain vulnerable to development. The gardens that exist today are generally clustered around the Near North Side, where poverty, unemployment, and food insecurity are high and development pressure has remained low. Based on the demographics of the Near North Side, the people most likely encounter the city’s gardens are low-income Black residents, however my spatial analysis revealed that gardens associated with citywide programs are also relatively more accessible for neighborhoods with higher rates of Hispanic and Asian/Pacific Islander residents than for neighborhoods that are largely white. These gardens appear to be concentrated where the greatest economic need is, but if development pressure in the disinvested neighborhoods were to increase, the gardens will be vulnerable to displacement. In Philadelphia, development pressure has increased quite dramatically in some neighborhoods, displacing gardens and residents alike. PHS’s effort to concentrate greening interventions in specific neighborhoods has proven the revitalization potential of urban agriculture. However, this revitalization focus seems to limit the benefits for the city’s poorest residents. Based on my spatial analysis, the program’s gardens are likely to be closer to neighborhoods with lower poverty rates and higher housing costs . Neighborhoods with more Black and Hispanic residents are more likely to have a garden nearby, cannabis growing equipment but the racial composition of many neighborhoods has also been in flux as property values rise, and Black residents appear to be gradually losing access to gardens in this process.
In Seattle, through the concerted effort of P-Patch program and nonprofit leaders seeking to maintain the program’s legitimacy, gardens have become more accessible for the city’s low-income communities over time. However, they have also become less accessible for immigrants, reflecting a pattern in all three cities where many foreign born residents seem to lack convenient access to programmatic gardens. Moreover, in Seattle the increasing access for high-poverty neighborhoods belies the fact that many people in poverty have been forced out of the city altogether, as property values have risen precipitously in recent years due to Seattle’s status as a world-class creative city—a reputation bolstered by the secure, widespread presence of P-Patch gardens. Thus, someone encountering a garden in Seattle today is more likely to have a high income, and while they might appreciate the social, environmental and aesthetic benefits of the garden before them, there are thousands of other people missing out on that experience because of the city’s changing economic condition. The individuals moving through the socio-environments in these three cities are unlikely to directly see the organizations that have helped to build and protect the city’s cultivated spaces, but as this dissertation shows, organizations in all cases have clearly played a role in shaping the flows of materials, ideas and people that converge to make urban agriculture and urban life more broadly. Electronic cigarettes , sometimes referred as “e-cigs”, “e-hookahs,” “vape pens,” and “electronic nicotine delivery systems ”, are rechargeable electronic nicotine delivery devices that are alternatives to smoking tobacco cigarettes. E-cigarettes consist of four parts: an atomizer , a battery, an e-liquid reservoir and an electronic control system. The atomizer heats and aerosolizes the e-liquid during the “vaping” process when the user takes a puff or presses the button; this generates a nicotine-containing e-cigarette aerosol that will be inhaled by the user for the purpose of nicotine intake.
Unlike traditional tobacco products, there is no combustion in the use of e-cigarettes, which eliminates the intake of tar and other harmful and potential harmful chemicals generated through cigarette or cigar smoking. In addition, the tar generated through conventional smoking which is extremely toxic to human and damages the smoker’s lungs through biochemical and mechanical process over a long time period 7-9 can also be eliminated through e-cigarette use. To date, e-cigarettes have been widely regarded as a “less harm” alternative to traditional cigarettes that can be used to help smoking cessation. However, the controversy of e-cigarette use has been increasing in recent years, since the beneficial link between e-cigarettes and smoking cessation is debated and emerging health issues had been found, related to the use of different kinds of e-cigarettes. It is noteworthy that thermal degradation products have been characterized due to the vaping process, some of which are known to have negative human health effects. The development of a nicotine aerosol generation device started in 1963, while the modern ecigarette was invented by a Chinese pharmacist Han Li, who thought of vaporizing nicotine containing propylene glycol using a high frequency ultrasound-emitting element, causing a smoke like vapor. E-cigarettes was first introduced to Chinese market starting from 2004, then entered the European and the US market in 2006 and 2007. The later design of the e-cigarette has changed from the earlier ultrasonic vaporization method to a battery-operated heating element. E-cigarette device design has evolved significantly since its introduction. The first-generation e-cigarettes use fixed and low voltage batteries, with a physical appearance similar to combustible cigarettes and are often referred to as “cig-a-like”. There exist two versions of the first-generation e-cigarette on the market, one is a two-part design, in which the replaceable atomizer and e-liquid reservoir are in one part, while the battery is separated in another part. The second style combines the atomizing unit, e-liquid reservoir and battery into one part. The first-generation product is still widely sold on the market. The second-generation e-cigarette typically has a larger variable voltage battery with a device referred to as a “clearomizer”. It has a removable atomizing unit with a filament, separated into a e-liquid reservoir and battery. The e-liquid tank of the second generation device has a larger volume reservoir compared to first generation systems, and can be refilled with different e-liquids. The third-generation e-cigarette, known as the “Mod”, has modified batteries that is able to vary the device power, voltage and, thus, temperature. It has a removable atomizing unit and larger e-liquid tank compared to the original clearomizers.
The Sub-Ohm tank with low resistance coils in atomizers is highly customized, as it is designed to create a large cloud with a strong delivery of nicotine and other additives. Stainless steel, nickel and titanium are typical materials used for the coil in third-generation devices, as these materials enable linear temperature changes with the adjustment of device power output. The fourth-generation e-cigarette is referred to as “Pod-Mods”, and contains a prefilled or refillable “pod” cartridge with a modifiable system. The compatible prefilled pod cartridges usually contain nicotine with PG/VG, THC or CBD as oils, and flavoring compounds. In addition to e-cigarettes, an inhalation device called a “vaporizer” is also available on the market; it applies non-combustion heat to aerosolize dry herbs or oil to release the active substance in these materials without combustion. Moreover, “dabbing” or “dibbing” is a specific term that describes the action or practice of inhaling small quantities of a concentrated and vaporized drug, cannabis drying trays typically cannabis oil or resin. It usually simulates the aerosolization process by placing the extracted THC oil concentrates on a hot surface. Since its first commercial introduction to the United States, sales in the e-cigarette industry has increased to $3.5 billion by 2015. The e-cigarette industry has greatly impacted the use of new tobacco products among youth. The prevalence of e-cigarette use among high school students increased from 1.5% in 2011 to 16% in 2015, which surpasses the prevalence of conventional cigarette use among high school students. According to a report by the Centers for Disease Control and Prevention in 2020, 19.6% of high school students and 4.7% of middle school students reported current e-cigarette use. Among current e-cigarette users, 38.9% of high school students and 20.0% of middle school students have used e-cigarettes on 20 or more of the past 30 days; 22.5% of high school users and 9.4% of middle school users reported daily use. Among all current e-cigarette users, 82.9% used flavored e-cigarettes. Investigators conducting toxicology and human health studies of acute and chronic use of e-cigarettes are struggling to keep pace with e-cigarettes’ popularity and product changes. The study of the health effects of these products is complicated by the fact that there are hundreds of e-cigarette devices and thousands of commercially-available e-liquids available to consumers. Further, the new generations of e-cigarettes have increased the flexibility of use for consumers by allowing any e-liquid to be added to the tank and a large range of variable power settings, which can increase the temperature of the device, as well as the output of vapor/aerosol and delivery of nicotine.
The composition of typical regular e-liquid for nicotine delivery usually include propylene glycol , vegetable glycerin , water, nicotine, and flavoring additives. PG and VG are typically used as solvents in order to produce an aerosol that simulates cigarette smoke. PG is a transparent and viscous liquid at room temperature with a sweet taste. It has very low volatility with a boiling point of 188 °C. The use of PG is generally regarded as safe for oral consumption, and it is usually used as a humectant and preservative in food, tobacco and the personal care industry. Moreover, PG is also used in the pharmaceutical industry as a solvent for drug delivery. Although it is widely used, the toxicology at a high concentration is increasingly recognized and recently reported. VG is a colorless and odorless viscous liquid with a boiling point of 290 ℃. It also has low volatility and a sweet taste, serving as a humectant, solvent, and sweetener in food, pharmaceutical and personal care applications. Both PG and VG have multiple hydroxyl groups,which results in the strong intermolecular force in the e-liquid and e-cigarette aerosol by forming multiple hydrogen bonds. Vaporization of PG and VG requires a relatively high temperature, although PG and VG start decomposing within the temperature range of e-cigarette use. The ratio of PG and VG in e-liquid varies in different products based on whether flavor or more aerosol mass or “cloud” is desired, while the most common two ratios are 50% PG/50%VG and 70%VG/30%PG. E-liquids containing more PG delivered more nicotine to these e-cigarette users. The chemical structure of PG and VG are shown in Scheme 1.1a. Nicotine is a chiral alkaloid produced in the nightshade family of plants, which has been widely used as recreational or anxiolytic compounds. Nicotine is a highly addictive compound that acts as receptor agonist for nicotinic acetylcholine receptors; its binding strength is better than the neurotransmitter acetylcholine. Therefore, nicotine is the equivalent to an increase in the amount of neurotransmitters, which results in increased secretion of dopamine from the reward center of the human brain. The average amount of absorbed nicotine per cigarette is about 2 mg, while the nicotine content of commercially available e-liquids varies from low to high . The chemical structure of nicotine is shown in Scheme 1.1b. Beside PG, VG and nicotine, most e-liquids contain flavor chemicals that have been certified as safe for ingestion in the food industry. The use of flavor compounds to create various flavor combinations is attractive to consumers. There are various chemical families of flavorants used on the market, including aldehyde , ketone , alcohol , monoterpene and ester . Animportant category is aldehyde, which has been recognized as “primary irritants” of the mucosal tissue of the respiratory tract. Behar et al. has identified that the most commonly used flavoring chemicals are menthone, p-anisaldehyde, menthol, cinnaldehyde, vanillin, and ethyl maltol, which has been found in 41 – 80% of commercial e-liquids. The transfer of these flavoring chemicals from e-liquid to e-cigarette aerosol is very efficient , while it has also been found that the refilled fluids that have lower concentrations of flavoring chemicals exhibit lower cytotoxicity, suggesting the toxicity of the e-cigarette aerosol is related to the concentration of theflavoring chemicals. However, with the significant increase in the array of different e-liquid products, it is difficult to comprehensively characterize all flavor compounds on the market. Previous research found flavor chemicals to be 1-4% of the total e-liquid volume, although the concentration of some specific flavor chemicals were sufficiently high enough to possibly be of concern for inhalation toxicology. Some specific flavoring chemicals like diacetyl has been found to cause adverse health effects to e-cigarette users, even if they are safe to digest.