Evaluation of Low-Cost CO2 Sensors Using Reference Instruments and Standard Gases for Indoor Use.

CO2 monitoring is important for carbon emission evaluation. Low-cost and medium-precision sensors (LCSs) have become an exploratory direction for CO2 observation under complex emission conditions in cities. Here, we used a calibration method that improved the accuracy of SenseAir K30 CO2 sensors from ±30 ppm to 0.7-4.0 ppm for a CO2-monitoring instrument named the SENSE-IAP, which has been used in several cities, such as in Beijing, Jinan, Fuzhou, Hangzhou, and Wuhan, in China since 2017. We conducted monthly to yearly synchronous observations using the SENSE-IAP along with reference instruments (Picarro) and standard gas to evaluate the performance of the LCSs for indoor use with relatively stable environments. The results show that the precision and accuracy of the SENSE-IAP compared to the standard gases were rather good in relatively stable indoor environments, with the short-term (daily scale) biases ranging from -0.9 to 0.2 ppm, the root mean square errors (RMSE) ranging from 0.7 to 1.6 ppm, the long-term (monthly scale) bias ranging from -1.6 to 0.5 ppm, and the RMSE ranging from 1.3 to 3.2 ppm. The accuracy of the synchronous observations with Picarro was in the same magnitude, with an RMSE of 2.0-3.0 ppm. According to our evaluation, standard instruments or reliable standard gases can be used as a reference to improve the accuracy of the SENSE-IAP. If calibrated daily using standard gases, the bias of the SENSE-IAP can be maintained within 1.0 ppm. If the standard gases are hard to access frequently, we recommend a calibration frequency of at least three months to maintain an accuracy within 3 ppm.

[Pollution Characteristics and Health Risk Assessment of Volatile Organic Compounds (VOCs) and Semi-volatile Organic Compounds (SVOCs) in Qiantang River's Hangzhou Section During a Water Odor Pollution Event].

For surface water samples collected from the Hangzhou section of Qiantang River (before, during, or after the occurrence of a water odor pollution event), 125 kinds of volatile organic compounds (VOCs) and semi-volatile organic compounds (SVOCs)were quantitatively determined via purge&trap-gas chromatography-mass spectrometry and liquid-liquid extraction-gas chromatography-triple quadrupole mass spectrometry. Then, the pollution characteristics of the VOCs and SVOCs were analyzed, and the health risk of these compounds was assessed. The results showed that 17 VOCs and SVOCs in the surface water samples of 4 monitoring sections were detected, in a concentration range of 0.01-1.21 µg·L-1, which is a low pollution level. The concentration of dichloromethane was the highest of 17 VOCs and SVOCs, accounting for 36.3%, and it was thus clear that dichloromethane was the main contributing factor. During the water odor pollution event, the concentrations of VOCs and SVOCs were significantly higher than they were in the three months before or after the occurrence of the event, by 2.1-4.6 times, reflecting the strong external source input. In addition, human health risk assessment of ingestion through drinking water and absorption through skin contact was performed using US EPA recommended methods. It indicated that the total non-carcinogenic and total carcinogenic risks (∑HI and ∑R) caused by VOCs and SVOCs are 2.4×10-3-3.6×10-2 and 1.9×10-7-1.0×10-6, respectively, both of which belong to the acceptable risk level. Therefore, although ∑HI and ∑R during the occurrence of the odor event were significantly higher than those in the three months before or after the event, the VOCs and SVOCs detected will not cause obvious non-carcinogenic nor carcinogenic health effects on humans.

[Pollution characteristics and health risk assessment of organochlorine pesticides (OCPs) in the water of Lake Qiandao and its major input rivers].

Organochlorine pesticides (OCPs) were quantitatively determined by GC in several surface water samples collected in July 2011 and November 2011 from Lake Qiandao (Xin'an River Reservoir) and its major input rivers. Then the component characteristics and source apportionment of HCHs and DDTs were confirmed, and the health risk assessment was evaluated. The results showed that 8 OCPs were found to be in trace amount, and p,p'-DDT, a-HCH and p,p'-DDE were the highest frequently detected OCPs. The concentrations of total OCPs in surface water of the studied Lake ranged from 1.9 to 7.6 ng-L-1 , which were at lower pollution level, and 1.2-212 ng.L-1 in the samples from its three major input rivers. The spatial distribution of OCPs in the water of lake was varying, and Xin'an River, the mainstream of the lake, was the main input source of OCPs. Also, different contamination patterns among sampling seasons were found, the concentrations of OCPs in surface water collected in wet period were higher than those in dry season, which display the characteristics of nonpoint source pollution. According to the ratio of feature components, the OCPs in surface water from the Lake Qiandao originated largely from long distance transmission or degradation of technical HCHs, while additional sources of DDTs existed in the region. In addition, human health risk assessment of ingestion through the drinking water and skin contact absorption was performed using EPA recommends methods, the carcinogenic and non-carcinogenic risks caused by OCPs were 0. 06 x 10(-7)-23. 2 x 10(-7) and 3.43 x 10(-5) -6.01 x 10(-3), respectively. According to the acceptable risk level, the carcinogenic and non-carcinogenic risks of the chemicals investigated can be considered negligible in water body of Lake Qiandao.

[Characteristics and evaluation of volatile organic compounds discharge in typical enterprise wastewater in Hangzhou City].

Totally 77 kinds of volatile organic compounds (VOCs) in inlet/outlet wastewater of 10 typical enterprises in Hangzhou City were determined by headspace-gas chromatography-mass spectrometry, then the discharge characteristics of VOCs were analyzed, and the monitoring results were evaluated. The results indicated that 22 kinds of VOCs were detected in inlet wastewater, the range of VOCs concentrations was 7-3.39 x 10(6) microg x L(-1), while 14 kinds of VOCs were detected in outlet wastewater, the range of VOCs concentrations was 16- 6.82 x 10(4) microg x L(-1). The concentrations of VOCs in inlet/outlet wastewater of flavors and fragrances manufacturing enterprises were much higher than those of other industries. When using the third class discharge standard of "integrated wastewater discharge standard" (GB 8978-1996) as the evaluation criteria, the toluene concentration detected in outlet wastewater of enterprise 1 was 2.45 x 10(3), microg x L(-1), which exceeded the standard limit. In addition. When the discharge multimedia environmental goals (DMEG(WH)) of VOCs in water was used as the evaluation criteria, the concentrations of n-butyl alcohol, isopropyl alcohol, acetone in outlet wastewater of enterprise 3 exceeded their respective discharge multimedia environmental goals.