The estimated concentration at this time would be the best estimate of the concentration if perfect instantaneous mixing had occurred. This estimated peak concentration was then multiplied by the room volume to provide an estimate of the source strength . Decay rates were determined by regressing the logarithms of the background-corrected concentrations over time. These rates reflect the effects of all particle dynamics on a given day, which include the deposition rates on room surfaces, the air exchange rate, condensation/evaporation of volatile substances, and coagulation. These mechanisms are also affected by environmental conditions including air flow rates in the room, temperature, and humidity. Removal rates were determined by subtracting the air exchange rates from the measured decay rates. Decays were followed for multiple hours. Over an 8-day period, a study of 24-h exposure was carried out using the PurpleAir monitors. Each day, a single puff of marijuana fluid was exhaled into this 30 m3 room following Protocol II . The door was closed during the 6 h following the puff, and open after that. Air exchange rates were measured by releasing a 10% mixture of CO into the room just prior to vaping and calculating the decline of the background-and temperature-corrected CO concentrations. Prior to the study and during it at intervals, two of the main monitors were zeroed,cannabis indoor grow system their impactors were cleaned and regreased, and flow rates checked. Since at least 2 monitors of each type were collocated, the agreement within each type could be determined, as well as the relative bias and precision .

For the two PurpleAir monitors at each location, there were two independent lasers within each monitor, so each monitor could be checked for internal agreement, and they could also be checked against each other.As part of that grant, the Stanford Institutional Review Board gave approval to the authors to carry out human experimentation. Since no human subjects were recruited for the experiments presented in this paper, telephone contact was made with a member of the IRB to obtain his opinion on whether IRB coverage of the authors was needed by the IRB. His advice was that IRB review is not required if the researchers doing the study are the only human subjects. In addition, the research is not medical, since its focus is on evaluating measurement methods and applying mathematical approaches to a class of indoor air pollutants, not on health impacts for humans. Finally, the emissions of every experiment were produced by a subset of the authors, who were experienced in inhaling both nicotine and marijuana smoke, and no persons were present in the room during the air pollutant decay periods. No other individuals participated in the smoking or vaping activities, nor were any persons other than the authors exposed to the aerosols produced. The source strengths for the high-heat Protocol II are about 3 times those for the low-heat Protocol I . These values of 3–9 mg/puff may be compared to measured values on the order of 1.4 mg/puff for a tobacco cigarette . The 3 instruments show fairly similar means, medians, and ranges, with no instrument significantly different from any other. The low-cost PurpleAir instrument also shows equally good coefficient of variation , as the two higher-cost instruments. Table 1 suggests that both the research-grade and low-cost optical air monitors can reasonably be used to determine the source strengths of marijuana vaping when applying suitable calibration factors to each monitor.

The calculated source strengths for the PurpleAir and SidePak instruments agreed well, with a slope of nearly 1 and an R2 value of 99% . Decay rates were measured for all experiments. The measured decay rates for the SidePak and PurpleAir monitors include air exchange rates a and deposition rates k, as well as other possible losses or gains due to evaporation, condensation, and coagulation: decay rate = a + k + other. If we subtract the observed air exchange rate from the observed decay rate, we are left with a term we call the “removal rate”, which is the sum of the deposition rate k and all other gain/loss mechanisms. The measured “decay rates” for the Piezobalance are actually the rates of mass accumulation on the crystal, and are affected by the evaporation from the crystal as well as the losses of the airborne fraction . The SidePak and PurpleAir decay rates were consistently maintained at a constant slope over the entire time following a single puff of the heated marijuana liquid—a time that extended from 1 to 8 h. The R2 values for these regressions were very high at an average R2 of 98%. However, the “decay rates” for the Piezobalance were typically constant for experimenter took a single puff from the vape pen with an 8:1 CBD/THC ratio at around 12:20 p.m. and then stepped out of the room. For the next 5 h, the aerosol was allowed to decay undisturbed. At around 5:40 p.m., the experiment was repeated. As can be seen, following an initial “false peak” due to unmixed air conditions, the SidePak decay rate settles down to a single value of about 0.52 h-1 for the 5 h.The line can be extended backward in time to the time of the puff. The intersection of that line and the time of the puff is the “true peak” that would have occurred under instantaneous perfect mixing. From the graph, the peak was about exp or 221 μg/m3 . In the second experiment, the decay rates were virtually identical . The “true peaks” were also similar and exp) or 221 and 245 μg/m3 . The Piezobalance also shows similar peaks for the two experiments, and similar decay rates following each puff. However, after the first hour, the decay rates increase and eventually the “concentration” goes to zero . Therefore, for the Piezobalance throughout all experiments, the decay rates were only calculated for the first 20 min following a puff.

This behavior is expected for volatile particles collected on the crystal undergoing evaporation, and can result in overestimating the actual aerosol decay rates . Decay rates are strongly affected by air movement. The use of a table fan approximately doubled the decay rates for both the SidePak and the Piezobalance . The use of two fans led to a further increase that was not, however, statistically significant. For building models of indoor exposure,cannabis equipment it is important to measure a and k separately. The mean air exchange rate was 0.128 h-1 . Data from the 8-day exposure experiment were examined to identify the time of elevated concentrations. Concentrations were considered “elevated” if they were associated with the time of vaping and were higher than typical concentrations during non-vaping periods . The elevated periods had a mean concentration of 62.9 μg/m3 and lasted about 9 h each day . The background concentration for PM2.5 was 4.5 μg/m3 . The 24-h average PM2.5 concentration was 26.5 μg/m3 and may be compared to the 24-h average outdoor standard of 35 μg/ m3 . The four main monitors used in this study had complementary strengths and weaknesses. Both optical monitors were able to count particles and estimate particle volumes. However, the resulting PM mass could not be determined from these two monitors without the use of a calibration factor. The mass could be determined both from the pump-filter and Piezobalance results. However, evaporation may be an important process and could only be determined from the Piezobalance. On the other hand, because evaporation from the Piezobalance presumably started soon after aerosol collection, only the early measurements by the Piezobalance could be used to estimate mass. In terms of 24-h average indoor concentrations, only the PurpleAir monitors could be operated continuously for so long, with the other monitors needing considerable downtime for maintenance. Two results from this study are required for building indoor air quality and exposure models: source strengths and removal rates. The source strengths shown by the SidePak and PurpleAir monitors ranged from 3 to 8.8 mg/puff. This is roughly 2–6 times that of tobacco cigarettes on a per-puff basis. Longer heating periods and correspondingly higher temperatures produced significantly higher source strengths, by about a factor of 3 going from 6 to 15 s of heating time. The example from this study showed that concentrations from a single puff could be elevated for about 9 h. Wu et al. found similar results comparing tobacco and marijuana smokers, with the marijuana smokers inhaling about 3 times the amount of tar and accumulating 30% more tar in the respiratory tract. Ott et al. used SidePaks in 60 experiments and found emission rates of 3.4–7.8 mg/puff for four sources of marijuana consumption compared to 2.2 mg/puff for a tobacco cigarette. Combination antiretroviral therapy has allowed people living with HIV/AIDS to maintain a high quality of life and achieve life expectancies near those without HIV . The optimal benefits of ART, however, cannot be attained unless persons living with HIV/AIDS are able to adhere to ART as prescribed . Non-adherence to ART is associated with poorer HIV suppression, decreased CD4 cell count, and an increased risk for antiretroviral drug resistance .

In addition to their impact on individual disease progression and health status, these consequences of ART non-adherence can also increase the likelihood of HIV transmission. For these reasons, accurate treatment monitoring with the goal of optimizing ART adherence is an issue of major relevance to the clinical care of PLWHA. Alcohol use is common among PLWHA, with an estimated prevalence of current heavy drinking of almost twice the rate of the general population . A recent national cohort study found that nearly half of PLWHA have a lifetime history of an alcohol use disorder . Excessive alcohol exposure in the context of HIV disease has been linked to higher viral replication and accelerated disease progression . Although the mechanisms underlying the impact of alcohol use on HIV disease remain under investigation, ART adherence is likely an important contributory factor . For example, one study examining the relationship between alcohol use and HIV disease progression found no direct association between alcohol consumption and CD4 cell count in participants receiving ART when controlling for ART adherence . Another recent study also failed to show a direct relationship between alcohol use and viral load detectability when controlling for other factors . The most robust evidence of the association between alcohol use and ART non-adherence in the literature finds that those who report any alcohol use are significantly more likely to be non-adherent compared to those who completely abstain from drinking , regardless of the amount of alcohol used . Although there is research examining the influence of level of alcohol use on medication adherence, results are inconsistent. Some studies have found significant associations between level of alcohol use and medication adherence , while others have found no difference in medication adherence between those with different levels of alcohol use . These studies have also measured level of alcohol use in many different ways. Some studies used continuous variables such as frequency of alcohol drinking and quantity of drinks , whereas others used categorical variables indicating the presence of an alcohol use disorder , binge-drinking , and risky drinking, which is often defined by a certain quantity of drinks per day or per week, though this quantity is also inconsistent across studies . A meta-analysis, attempting to shed light on these inconsistencies among PLWHA, found that individuals who either meet probable current AUD diagnosis, or the National Institute on Alcohol Abuse and Alcoholism criteria for at-risk drinking were about half as likely to be adherent to medications compared to otherwise . A recent systematic review also consistently found that AUD diagnosis was associated with decreased ART adherence across studies; however, AUD diagnostic criteria differed across studies . These findings still do not clearly parse apart different levels of alcohol use in association with ART adherence in the context of those who use alcohol. The current study examined the association between at-risk alcohol use and ART adherence among PLWHA who reported drinking at least once in the last 30 days. By excluding non-drinkers, this study attempted to elucidate whether at-risk drinkers were more likely to be ART non-adherent compared to those who drank less .