Long-term monitoring of wet, dry, and bulk atmospheric deposition in central Arizona-Phoenix, ongoing since 1999

The aims of this study are to examine (1) the magnitude and spatial variability in the concentration and flux of wet deposited major ions (NO3-N, NH4-N, DOC, PO4-P, Cl, SO4, H+, Ca, Mg, Na, K) across the greater Phoenix metropolitan area, including the developed urban core and outlying desert, and (2) patterns of coarse dry particulate deposition across stated area and provide some minimum estimates on levels of dry deposition of these ions. This study was designed particularly to answer the question: 'To what extent are concentrations and fluxes of these ions enhanced at sites within the urban core relative to undeveloped desert sites upwind and downwind of the city?'. At the outset, the project featured eight wet-dry collectors positioned spatially so as to form a transect running approximately west-to-east across the central Arizona region from outlying desert to the west, upwind of the prevailing synoptic wind direction, through agriculture to urban core sites, and, finally, to two downwind sites in the desert to the east and northeast. As much as possible, these collectors were co-located with Maricopa County or Arizona Department of Environmental Quality monitoring stations. Monitoring at most sampling locations ran from 1999 through the mid-2000s when sampling was discontinued at several sites. Sampling continued at the Lost Dutchman State Park, also a Desert Fertilization experiment site with a focus on atmospheric deposition, through 2016. Sampling continues at a site on the Arizona State University Tempe campus that was added to the program in 2009.本研究旨在达成两项核心目标：其一，探究大凤凰城都会区（涵盖建成城区核心与外围荒漠区域）内湿沉降主要离子（NO3-N、NH4-N、溶解性有机碳（DOC）、PO4-P、Cl、SO4、H+、Ca、Mg、Na、K）的浓度与通量的量级及空间变异性；其二，明确该区域内粗颗粒干沉降的分布模式，并对上述离子的干沉降水平给出最低限度估算。本研究尤其针对如下问题展开设计：相较于城市上风及下风方向的未开发荒漠站点，城区核心内的站点中上述离子的浓度与通量会在多大程度上得到提升？ 项目伊始，共布设8套干湿沉降采样器，其空间布局形成一条近似东西向的样带，横穿亚利桑那州中部区域：从主导天气风向上游的西部外围荒漠出发，途经农业区至城区核心采样点位，最终延伸至东部与东北部荒漠内的两个下风方向采样点位。在条件允许的前提下，这些采样器均与马里科帕县或亚利桑那州环境质量部的监测站点同址布设。绝大多数采样点位的监测工作于1999年至2000年代中期开展，期间部分点位的采样工作先后终止。位于失落的荷兰人州立公园的采样点位（同时也是聚焦大气沉降的沙漠施肥实验站点）的采样工作则持续至2016年。2009年加入本项目的亚利桑那州立大学坦佩校区采样点位的采样工作目前仍在进行中。